SOUND RECORDING FOR AMATEURS - World Radio History

1.r.artirell and .4 inaleur Wireless, August 1st, 1936.

SOUND RECORDING FOR AMATEURS

Vet, S. Ns. 202.Esty,-,cs, 1st, 1910. PRACTICAL TEiEVISION

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THE HOME MECHANIC ENCYCLOPIIEDIA1With By F. J. CAMIV1 (Editor of " Practical Mechanics," etc.)

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ii August 1st, 1936PRACTICAL AND AMATEUR WIRELESS

Also Prizes of

PHOTO -ELECTRIC EXPOSUREMETERS

" WESTEX " TRIPODS

" ROLBAC" LOOSE-LEAFALBUMS

" ENSIGN " PRINT TRIMMERS

"PHEW-IT'S HOT is the subject of the contest, which offers unlimited

opportunities for the exercise of ingenuity and artistry. The pictures

you send in will NOT be judged entirely on their technical quality, but

also on the originality or humour shown by you in their arrangement

Get ready to take your picture or pictures-it doesn't matter whether

you have a camera costing a few shillings or one worth pounds-you

stand the same chance of winning as any other competitor

Full particulars and success tips in the July and August numbers

The helpful photographic journal which tells you how to make betterpictures AND HOW AND WHERE TO SELL THEM !

AT ALL NEWSAGENTS AND BOOKSTALLS

August 1st, 1936 PRACTICAL AND AMATEUR WIRELESS 501

SOME QUALITY CIRCUITS "EvirE

Technical Staff:W. J. Delaney, H. J. Barton Chapati, W11.110.,

B.Sc., A.M.I.E.E., Frank Preston.

VOL. VIII. No. 202. August 1st, 1938.

ROUND the WORLD of WIRELESSRadio Life-saving

EXPERIMENTS carried out in Kenthave shown that an ultra -short-wave

transmitter and receiver will form a valuablelink between the pit head and the workingsat the bottom of the mine. A wavelengthof 4.5 metres was used in the tests, andtwo-way communication (telephonic) wascarried out, the depth of the pit which wasused being 2,160ft. It was also foundpossible to carry out conversations betweenthe shaft bottom and workers situated2,000ft. away in a remote part of theworkings. The apparatus used weighedonly 151b.

Western TransmitterTHE B.B.C. propose to build a new

Regional transmitter at Start Point,in Devon, to supply the Western counties.This transmitter will take the place of thosenow in use at Plymouth and Bournemouth.The present Western Regional transmitterwill probably then be retained solely forthe Welsh programmes whilst the newstation will serve a much greater area thanis now covered by the two relay stationsjust mentioned.

Dublin Interval SignalDUBLIN is still waiting for its interval

signal. It was proposed to use thefirst nineteen notes of the tune " O'Donnellabu," but when the apparatus arrived itwas found that the tune was ratherineffective and, therefore, it has been sentback for lengthening. It is now unlikelythat the tune will be on the air for at leastanother month.

New Detector SystemsALTHOUGH the present method of

detection is a relic from the veryearliest days, there are several schemes nowincorporated which may be regarded asmodern inventions or improvements. FromFrance, however, news now comes of atotally new system of detection, which isclaimed to combine all the advantages ofpresent systems and which promises tobecome standard practice in future designs.An interesting book dealing with anothersystem of detection has also been issued inthis country, and gives some interestingdetails of experiments carried out by aMr. D'Arcy Ford.

Ulster Radio ShowN view of the fact that the R.M.A. pro-Iposes

not to support provincial radioexhibitions the Ulster Radio Wholesalers'Association have called a meeting and havedecided to co-operate with other localbodies to organise a radio exhibition. Ifthe resolution is carried the exhibitionwould probably be held at the Plaza, Bel-fast, for ten days, commencing September14th next.

Television In RussiaTELEVISION is progressing in the

U.S.S.R. and the Soviet Radio Com-mittee have decided to put up three

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i RAD IOLYMPIAiii AUGUST 26th 1

1 TO

i SEPTEMBER 5th 1

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television transmitters'this year, in Moscow,Kiev, and Leningrad, whilst a mobiletransmitter is also being built. It is alsoproposed to put up other transmitters toserve the districts of Khabarovsk, Novosi-birsk, Tashkent, and so on. Televisionreceivers are being designed and are to beput on the market, but no detaild are yetto hand concerning the wavelengths, pic-ture definition, or other important data.

Believe It or NotAMATEURS in this country are often

intrigued by the names given tovarious American receivers, such as the" Go -Getter," and " Hotter Dog," etc.,but a recent magazine from that countrydescribes a Three -stage Tri-Tet Exciterwith Regenerative Quadrupling Amplifierusing Suppressor -grid Feedback !

Marconi-Ekco CompanyTHE Marconi Wireless Telegraph Com-

pany and Messrs. E. K. Cole, Ltd.,are forming a jointly -owned companycombining the manufacture and technicaland research activities of the two com-panies for the production of measuringinstruments, diathermy and electro-medicalapparatus. The company is to be known'as Marconi-Ekco Instruments; Ltd., witha nominal capital of £5,000.

Television at OlympiaAT the time of going to press we learn

that the R.M.A. are considering theerection of ultra -short-wave aerials atOlympia to enable advantage to be takenof the television transmissions should theycommence in time for the Exhibition.

Changes in the BandCERTAIN contracts terminate this

month, and the combination nowemployed by Henry Hall in his famousband will undergo some changes. MissVivienne Brooks is leaving, and the typeof programme to be broadcast will undergoa revision. This, no doubt, promises toresult in a general improvement in thedance programmes, as well as in the lightertypes of broadcast.

Zeesen Short-wave TransmitterANEW transmitter is to be opened at

Zeesen in order to enable the broad-cast of the Olympic Games to be carriedout in all possible languages. This newstation is claimed to be the largest andbest equipped in the world and is now near-ing completion.

Bicycle RddioALIVERPOOL firm has produced a

novel receiver for use on a cycle andthe local Watch Committe has placed anorder for eighty of these receivers for theuse of the police force. Does the policemanwear headphones whilst. riding ? We cannotimagine a loudspeaker on the machine,and at the same time it would be ratherrisky riding through traffic whilst wearingheadphones, but, no doubt, the makershave made suitable provision, and theapparatus must be very effective in view ofthe large initial order which has beenplaced for these machines.

502 PRACTICAL AND AMATEUR WIRELESS August 1st, 1936

THE PICK of the PROGRAMMESColdstream Guards BandTHE Band of His Majesty's Coldstream

Guards has been broadcast severaltimes in the Midlands, chiefly as outsidebroadcasts. On August 4th it will playfrom a Birmingham studio. The pro-gramme is to open with the first broadcast

MAKE THESE DATESWITH YOUR RADIO

Follies " broadcasting from the, ArcadianPavilion, Morecambe, and a variety actfrom the Winter Gardens. -

ROY FOX LISTENS -IN

Roy Fox, the famous band lido', has a Pye All -wave receiver demonstrated to him by Mr. A. G.Waterkamp, manager of the Plymouth branch of Messrs. Godfrey & Co., Ltd., who installed this

model in his dressing -room at the Palace Theatre.

performance of a March, " Stratheden,"composed by Lieut. J. Ca,usley Windram,the regiment's Director of Music, who willconduct. The Coldstream Guards havehad an enlisted band since about 1783.For a number of years prior to that dateit had civilian bands. Notable events inthe band's recent history have been aCanadian tour and the fact that it repre-sented British Army bands at the funeralof Marshal Foch.

Dance and SerenadeJEAN SALDER and his Serenaders, who

have had a number of broadcasts thisyear, are to give a programme on August5th, entitled " From the Hills." This bandis engaged at a Birmingham hotel.

Tony's Pied AcesPAYNE'S Majestic Ballroom is known

to everyone who has visited Llan-dudno. It has accommodated many cele-brated dance -band leaders. The presentband connected with the Majestic Ballroomis Tony's Red Aces, who will broadcaston- August 1st. This band made its debutOn the air from the Midland Regional inNovember, 1934, and since then it hasbroadcast over one hundred times.

Morecambe on the AirON August 6th Mark Sheridan's " 1936

Frolics " will broadcast twice fromthe Palace Theatre, Morecambe, once *inthe afternoon in the main Regional Pro-gramme, and again in the evening as partof a special " Morecambe Night's Entertain-ment".for Northern listeners only. Thelatterprogramme will include the "Arcadian

Four Years of BroadcastingON August 2nd, in the North Regional

programme, the orchestra of theNew Victoria Cinema, Bradford, under thedirection of Sydney Phasey, completesfour years of regular weekly broadcasts.Mr. Phasey's team will continue to broad-cast this season., It is interesting torecall that the director made his debut atthe age of fourteen by playing violin solosat the Metropolitan Temple in New York.

503 EINE 1111PROBLEM Np. 202.

Walton's superhet stopped functioning andalthough he suspected' that the* frequency -changing valve was not oscillating, he foundthat this valve showed continuity across itsfilament pins and passed anode current.What easy method could he have adopted tofind whether -the valve was oscillating ?Three books will be awarded for the first threecorrect solutions opened. Address yourletters

.1 to the Editor, PRACTICAL AND AMATEURWIRELESS, George Newnes, Ltd., 8-11,Southampton Street, Strand, London, W.C.2.Envelopes must be marked Problem No. 202In the left-hand *corner and must be postedto reach this office not later than the first postTuesday, August 4th, 1038.

Solution to Problem No. 201.320 ohms is the resistance specified by the manu-

facturers for the 41 M.P., but when two of these valvesare used in push-pull, the value of the common biasresistance must be halved, as the current taken by thetwo valves is passed through it.

The following three readers successfully. solvedProblem No. 200, and books are accordingly beingforwarded to them : M. B. Ember, 6, Clifton Ilhigs.,London, E.2 ; J. D. Morris, 17, Lynton Rd., HeatonMoor, Stockport; J. Harris, 835, Beanwood Rd.Beanwood, Birmingham.

Dance Band from MalvernON August8th, in the Midland Regional

programme, Billy Gammon and his,Star Players, who arehaving their secondsummer at the Winter Gardens, malveni,.will be heard playing from the FestivalClub there. This combination has hadresident winter engagements at CheltenhamSpa since 1934.

Western SalonTHE second concert in the series

" Western Salon" 'will be broadcastfrom the orchestral studio at Bristol beforean audience on August 5th, when theartists will be the- Bristol Chamber MusicPlayers, who are Joan Allen (violin),'Madeline Jacobi (viola), Olive Woodington(violoncello), and Winifred Davey (piano-forte), and they have taken ,thename of" Players " so that the combination canbe,augmented to_ a quiAtet or sextet ifdesired.

Variety from HanleySTEFFANTS Sixteen Singing Scholars

are the principal item in the MidlandRegional program -Me on AuguSt:4tV,in avariety bill froni the Theatfe ROyal,Hanley.

Evelyn 'Hardy:. and her Ladie's7-:134rid'THIS1 broadcast am 'the Manor Gardens:

.

-Exmouth, on August 3rd. The bandbroadcast last year- from Crewkerne, andlisteners have also heard it fromMinehead.

An Ex -Cowboy's ExperiencesIN the Midland Regional programme 'on1 August 4th, in the " Seeing Life " seriesof talks, B. K. Vallings is to relate hidexperiences as a cowboy and packer in5Western Canada. Mr. Vallings, who isnow in charge of the Shropshire campaignagainst the musk rat, has broadcast enter-taining stories of rodeo in the West.

R.U.C. BandTHE Band of, the Royal 'Ulster. Con,

stabulary, wbich is tQ broadcast' onAugust 6th by permission of R. D. Harrison;0.B.E., Commissioner of ,Police, will heunder the directorship of -District InspectokGeorge C: Ferguson. The band consistsof thirty-six players recruited mainly froM:military bands, and representing twenty:,eight separate battalions. 'The band inay,frequently be heard in, the public parks inBelfast ; it plays at many, official 'functionsand has broadcast on Several occasions inthe Northern Ireland programnies. Theprogramme includes the " 13allet Egyptien,";by LuiginV melodies from " Patience,';and Allegro marziale (Nautical Moments);by Winter. There will be a baritonesoloist, William J. Breakey, and ConStableJ. Orr and: .E. MCICenna.will play a duetfor piccolo and clarinet.

Symphony ConcertU. FOSTER CLARK will conduct the1 1 B.B.C. Midland Orchestra in a Sym-:phony Concert on August 7th. The worksto be given are Symphony No. 29, in A,by Mozart, and Job," a masque fordancing in nine scenes by Dr. Vaughan -Williams. -

August 1st, 1936 PRACTICAL AND AMATEUR 'WIRELESS 503

BuildinWHEN a valve is get in oscillation,

its anode current changes. Forinstance, if a valve in a quiescent

state passed 4 mA., putting it into violentoscillation by coupling tuned grid andanode coils may cause it to pass double ortreble this current, say, 9 or 12 mA.

This current change is used in the deviceto be described. In the anode circuit ofan oscillating valve is placed a relay thatmakes or breaks a following circuit accord-ing to whether 4 mA. or 10 mA. is passingthrough. This change of current is causedby affecting the valve's oscillation intensityby means of hand-capacity-well knownas the bug -bear of ill -designed short-wavereceivers.

It thus becomes possible to operate therelay, and hence any distant piece ofapparatus connected with it, simply byapproaching or withdrawing one's handto or from a sensitive part of the oscillating

Figs. 1 and 2.-Details of the coil, and the

valve unit. This sensitive part may beconnected by a thin, unobtrusive wire to aconcealed foil plate that provides thecapacity _effect, and the oscillating unititself may be concealed, so that the wholebusiness becomes very mystifying toanybody not " in the know." This is theprinciple upon which the apparatus works.

Constructing the CoilsThe valve unit is made to oscillate at a

high frequency, in the region of 40 metreswavelength. This is so that any hand -capacity effects become much more markedthan they would be at a lower frequency :the susceptibility of short-wave receiversto hand -capacity is notorious but in thiscase useful.

The grid and anode coils consist of sixturns each of, 22 -gauge enamelled wire on a2in. diameter former, the turns beingslightly spaced and the coils close alongsideOne another. Fig. 1 will make this clear.If one of those old 6 -pin formers' and itsbase holder are available, they will doexcellently.

The other components needed are anon -inductive condenser of about .01 mfd.,an on -off switch and a few terminals.They, and the coils and valve holder (4 -pin)are mounted on a suitable baseboard andwired up as shown in Fig. 2.

This completes the oscillating unit.Preliminary adjustments are made byconnecting a 25 mA. meter and H.T.battery in the anode circuit, as shown bythe dotted lines, and switching on. About100 volts H.T. will be needed. If the valve

the "MaThe Device Described in this Article

Enables Distant Apparatus to be IControlled by "A Wave of the

Hand." It is well within the Abilities .!

of the Amateur Constructor. ;

By W. H. CAZALY

-it may be almost any 2 volt H.F. ordetector type valve-is oscillating properly,some 10 or 12 milliamps of current will bepassed. The coupling between the gridand anode coils should be adjusted, bycarefully closing up or opening out theturns on one of the coils, until about thisvalue of current is being passed. Theadjustment could be done by adding preset

condensers, of .0001fivz PLATE maximum capacity, one

across each coil, and ad -.:7' justing them by means

.4761/47-1" of their screws, but theself -capacity of the coilsis really sufficient, ifcare is taken over ad-justing the turns spacing.

It will be noted,while making these ad-justments, that as soon

o as either the grid of the

oanode of the valve is

of r7Fotouched, or even if the

I hand is brought close tpj;_ 4.4., the coils, the anode cur -1 - tent changes, since the

intensity of oscillationcircuit which is employed, is altered. This is exactly

the effect we are aimingat. When left to itself, with nothing of aconducting nature within three feet of it, theunit should pass about 10 mA. When thegrid or anode is touched, the current shoulddrop to about 4 mA.' Various anodevoltages should be tried, between 120 and80 volts, until the most sensitive arrange-ment is found. It is the change of currentthat matters : it is better to drop from10, mA. to 4 mA., which is a change of6 mA., than from 20 mA. to 17 mA., whichis a change of only 3 mA., or from 6 mA.to 4 mA., which is a change of only 2 mA.

The RelayThe relay is made out of an electric

bell, which may be second-hand, if it is agood one Cheap and nasty bells will not

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C Hand"do, because their make -and -break contactsare usually of inferior metal merely platedwith a resistant metal which is quicklyburnt off in use, or is removed whenattempts are made to clean these points.

The clapper is cut off short at thearmature and the gong removed, a's if thebell were going to' be used as a buzzer.Then the bobbins are removed, the wiretaken off, and 40 -gauge enamelled wirewound on in its place, completely filling thebobbins. This is easily done with ahand drill or one of the simple windinggadgets that have been described fromtime to time in this journal. Care must betaken when joining the wires of the twobobbins that the sense of the windings iscorrect, otherwise the- magnetism of thepole pieces will be incorrect. The directionof the windings is shown in Fig. 3, and theconnections in Fig. 4.

AdjustmentsWhen the oscillating unit and the relay

have been constructed., they should bemounted together -on a baseboard andlinked up in accordance with the diagramin Fig.- 5.- The insulating condenser, non -

.inductive and of .0005 mfd. capacity, ismounted close to the valve anode andconnected to it, .and from the other side ofthis condenser a 12ft. length of 36 gaugeenamelled wire is taken; the end of thiswire is soldered to a plate of tin or copperfoil. This plate is 3in. square. It can beplaced anywhere out of the way, as long

as it and the wiredo not lie close tometal objects such Foieas tools, pipes or giron work.

Now the oscil-lator is switchedon. There shouldbe about 10 mApassing throughthe relay mag-netising coils ; itmay be necessaryto plug in at 120volts in the H.T.battery instead ofat 100 volts inorder to overcomethe resistance ofthe relay coils.This should beenough to pullthe armature to

_the pole pieces,(Continued overleaf)

Figs. 3 and 4.-The relay and method of connection.

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Fig. 5.-The completedapparatus.

'504 PRACTICAL AND AMATEUR WIRELESS August 1st, 1936

-RUILDING THE "MAGIC HAND"(Continued from previous page)

thus breaking the circuit that lights theflash -lamp bulb. As soon as -the foil square istouched, the armature should be releasedfrom the pole pieces, flying back andclosing the flash -lamp bulb circuit so thatit lights up. If this, action does not takeplace properly, first try different tappingson the H.T. battery, and then carefullyadjust the armature spring and the screwcontact point against which it presses. Itis sometimes a help to stick yery thinpaper-cigarette paper-over the ends ofthe pole pieces, so that the armature isonly held very lightly with _the, 10 mA.Passing, and quickly released when theCurrent falls. This also prevents anyresidual magnetism in the poles or armaturecausing it to stick. These adjustments arecarried out until it is sufficient only tobring thehand within half an inch of thefoil stingi4 to make the armature fly backand close the light Circuit.

It may be found that even when theaction seems to be quite in order theflash -lamp bulb does not light up properly.This is due to poor contacts' in the relay.They should be very gently cleaned withmethylated spirit on a piece of card toremove grease and then very lightly rubbedwith the finest of emery cloth.

Using the RelayHaving succeeded satisfactorily in switch;

ing on and off a flash -lamp bulb, manyother amusing and mystifying effectscan be produced with ingenious devicesoperated by therelay. The authorhad one of thesehand -capacity re-lays working forweeks in a shopwindow, using aneliminator insteadof a H.T. batteryfor economy sake.

The oscillatorand relay wereconcealed behindshow receiversandshowcardsand the wireand foil plate weretaken behind sidecurtains to acardboard"hand" stuck off the inside of the plateglass window. This " hand ", consisted oftwo pieces of card stuck together with thefoil between them. Passers-by were invited,by a notice above the " hand," to placetheir own hands over this 'hand," outsidethe glass-and to listen. When they did

.Eks4.1"Caw-,4cr.s.

Fig. 6.- H ow therelay may be usedto operate the

loud -speaker.

this, a powerful mains receiver standing -,.in the doorway abruptly emitted w4teverprogramme it was timed -to. Wheh thestartled people removed thcie;...hands, itstopped, and mystification was complete.

This effect was obtained b makrg the-i.

relayclose the- speech -coil cuit "in the

manis receiver's loud -speaker, connectionsbeing:made as shOwn in Fig F 6. The receiverwas_ switched on, all the time, so that itwas unnecessary -to wait for the valvesto warm up, and the 6 -ohm resistance wasplaced across the output transformer to pro-vide a load to avoid damage to the receiver.

It should be noted that where the foilis to be mounted behind a'shop window, andperhaps to be obscured by cardboard or othercut-outs between it and the glass, thecapacity between the foil and the ,body -ofthe operator will be considerably reduced;and therefore the initial adjustments shouldbe carried out by providing a similar capa-city change, rather than by actuallytouching the grid or anode. Such tests -will avoid the possibility of failure whenthe apparatus is finally installed under theabove conditions.

Strings of " fairy" lights, moving signs,working models driten by -eleetric motors,gramophones, hooters, all sorts of apparatusof an amusing or useful . kind can thus beoperated simply by passing a. hand acrossthe foil square.

TI -1E NEW FER ANTIA New de -Luxe Superhet Radio-gram Designed to Cover AllWavelengths and some DetailsCADIA" RADIOGRAM of fhe New MagnascoPic Dial

THE new season's Ferranti receiverspossess some novel features, and theaccompanying illustration shows the

Arcadia radiogram which employs. a super -het circuit covering the short ' waves inaddition to the normal broadcast waves,and is fitted. with 'a variable selectivitydevice. The superhet is of the 8 -stagetype and covers the short waveband from19 to 51 metres, and the variable selectivitycircuit which is fitted is of a patented typein which a self -resetting device is included,and this makes it impossible to retunethe receiver except in its most selectivestate. As most amateurs are probablyaware, the selectivity of a superhet may bevaried by several methods, one of whichis to modify the coupling between theprimary and secondary windings of theintermediate -frequency transformers. Ifthe coupling is increased so. as to givemaximum selectivity there would be adanger of forgetting that the adjustmenthad been made, and upon searching for aweak station it would be found impossibleto pick it up -until the coupling was in-creased. This renders it difficult to usesuch a receiver unless the user is fully awareall the time of the various changes whichare made. The Ferranti device overcomesthis defect and provides the listener with afool -proof adjustment Which may alwaysprovide maximum results, no matter inwhat direction they are required.

The Magnascopic DialA further new feature which is introduced

in the new receivers, and which is intendedto simplify tuning on the short waves, isin the form of a small additional dialsituated above the main tuning dial. The,effect of this new scale is to increase thelength of the normal tuning dial to over6ft., and this is carried out by an interestingsystem of mirrors and Tenses. Attachedto the main condenser Spindle is a trans-

parent semi -circular scale of about thesame size as the ,old -type tuning scale, andthis is engraved with the wavelengthswhich are shown on the normal tuning dialand which range from 19 to 51 metres.The usual sub -divisions are, of . course,included. The normal dial -illuminatinglamp is so placed that its rays are concen-trated by a lens on to the additional scale,and they pass through this and through afurther lens on to a mirror inclined at 45°to the horizontal. This mirror is, of course,

immediately in front of the tuning condenserand it directs the reflection of the dial inan upward direction, where it strikesanother mirror arranged at a similar anglewhich directs the reflection in a forwarddirection so that it strikes an opal screenimmediately behind the additional aperture.Upon this the settings of the dial are thenseen in a greatly magnified form, and thusone of the great bugbears of short-wavetuning is removed. This device is nowfitted to all of the Ferranti superhets.

The 26 -guinea Arcadia All -Wave_ A.C. Variable Selectivity High -Fidelity Radiogram.


Experiments inUniped Control

Various Components Which Form an Essential Part of the

Modern Radio Receiver may be Linked Together to Reduce

the Number of Controls. Some Suggestions are Given Here

By W. J. DELANEY

THE ganged condenser is now familiarto every listener, and it is commonknowledge that the separate sections

of this component are employed for tuningtwo or more separate coils. The actual

quired difference at various wavelengths,whilst the condenser which tunes theoscillator section has the plates of a differentshape, or the condenser for this particularpurpose is used in conjunction with other

condensers (fixed) to pro-vide the required capacityvariation.

Fig. 1-A circuit which has been tested andproved-The combination of an H.F. volume

control and a reaction condenser.

process of tuning these separate circuitsis a rather complicated one, especially',when a superheterodyne receiver is con-sidered, and the degree of variation atdifferent parts of the tuning dial has tofollow a complicated law. That the'difficulty is not insurmountable is obviousfrom the fact that every modern superhet

a ganged tuner, and in somereceivers there are no fewer than four sepa-rate coils so controlled, each circuit varyingthroughout the scale. For the benefit ofthose readers who do not know how this;process is carried out, it may be brieflystated that the end plate in each ordinary`section of the condenser is split into anumber of separate sections and theseseparate sections are individually adjustedby the manufacturers to provide the re -

Reaction CircuitsThe normal tuned -grid

circuits are not the onlyones to which this devicemay be applied, although,owing to the difference incoils and circuits, it is notpossible to purchase ready-made dual controls. Whena standard broadcastreceiver is examined, how-ever, it will be found thatthere are several separatecontrols which may easilybe removed if only somesimple way of linking themwith another control can befound. I am leaving out, forthe purpose of this article,such items as ganged

GANGED

Fig. 2.-The aerial condenser may be ganged withthe tuning condenser.

switches for radio and gram. change -over,and ganged on/off switches and volumecontrols, as these are now well known. The

8.7:-/- Fig. 3 (left).-In this cir-

cuit the reac-tion is pre-setby means of thecondenser, andthe H.T. feedis varied in con-junction withthe tuning con-

denser.

Fig. 5 (right).Resistance con-trolled reactionand H.F. vol-ume control-a modification

of Fig. 1.

GANGED

Fig. 4.-A reaction condenser ganged with thetuning condenser.

following details will, however, form thebasis for experimental work by the keenamateur who is anxious to develop a receiverof a type which cannot be purchased, and itwill be seen later that some very interestingtests may be carried out in an endeavourto remove one or more controls.

Dealing first with the reaction circuitas used in the normal grid -leak detectorstage, it will be found in practically everyreceiver that as the wavelength to whichthe grid circuit is tuned is increased, somust more reaction be employed. That isto say, if the circuit is tuned to 200 metresand the reaction control advanced untilthe receiver is just off the oscillation point,upon tuning the circuit to 300 metres itwill be found that the reaction control maybe advanced a few degrees further beforeoscillation takes place. Thus, when search-ing for a station with the set in the positionof maximum sensitivity, it is normallynecessary to adjust both tuning and reactioncontrols togetherwave range.

Dual ResistancesA normal reaction condenser may be

linked with a tuning condenser so as toprovide this position of maximum sensi-tivity as a constant factor from minimumto maximum wavelength, but there areother more interesting methods of carryingout the same effect, as it will probably befound that with the correct capacity ofreaction condenser the required couplingcannot easily be obtained.

Two -section resistances (or volume con-trols) are already on the market and areobtainable in various values. By adopting

(Continued overleaf)

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506 PRACTICAL AND' AMATEUR' WIRELESS .AugUsf 1st,: 1936EXPERIMENTS IN UNIFIED CONTROL

(Continued from previous page)

a resistance to control reaction a dual-purpose,unit may be employed in.a circuitof the type shown in Fig. 5, theremaining section of this unit being thenemployed for the variable -mu grkl-hiascontrol in the H.F. stage. Other methodsof using the resistance for the control ofreaction are shown in -Figs. 3 and 6, andin these the resistance may be ganged withthe tuning condenser, provided that suitablecomponents are chosen.

A Novel Arrangement.In Fig. 6 a novel arrangement is shown

in which the control of reaction is carriedout by means of a resistance and this isganged with the tuning control; the degreeof reaction being governed by the H.T.,the size of the reaction, condenser and itsrelation to the grid winding. The fixedcondensers -is inserted to prevent a short-circuitof the4H.T. battery. The combina-tion of the normal reaction condenser witha resistance to .vary the H.F. grid bias hasalready been dealt with, and a dual unitfor this purpose was employed in our ThreeStar Nicore, although, unfortunately, thedual component is no longer on the market.

The Aerial InputThe degree of damping which is exercised

by the aerial -earth system varies accordingto the wavelength to which the circuit istuned, and it will be found that by including

a variable condenser in the aerial circuit,maximum results,may he obtained at everywavelength if the condenser is suitablyadjusted. Thus this -condenser may beganged with the tuning condenser, althoithin this case it will be found that._ as thecapacity of the tuning condenser is increasedthe capacity of the aerial condenser mustbe decreased, and thus the two componentsmust be linked together with care.

In all of the schemes just outlined,experimental work is . called for and noexact values can be given, as they will vary

Fig. 6.-Another farm of resistance -controlled reaction which maybe operated with the tuning condenser. 4

for each individual circuit. Furthermore,in some cases it may not, be-found-possibleto obtain suitable components which mayreadily be converted for use in the dualarrangement, -chiefly owing to the factthat components with double -ended spindlesare not now generally manufactured.Certain short-wave tilling condenseta.areObtainable with spindles at each end, andmay be employed for reaction pnrposes,and Messrs., Varley manufacture Variableresistances with a 'lengthened, spindle for,ganging purposes. In other types of volume

control it will generally befound that by removing theend cover the spindle maybe found accessible, and inmost cases provision willhave been made by themanufacturers for the at-tachment of a switch, andthis will enable the experi-menter to carry out one orother of the above Schemes.Coupling units are availablefrom several firms; and ingeneral are designed for twolin. spindles a4nd thus are notreadily adaptable to everycase. A little thought will,however, enable some deviceto be constructed to enablethe ideas which have beengiven to be enlarged upon ortried out and will undoubt-edly provide some hours ofin-teresting experimental Work.

C

ONDITIONS, unfortunately, duringthe past fortnight have not shownmuch improvement over the

previous period, and atmospherics due tothe numerous storms which have beenraging over the continent of Europe havenot, made DX listening too pleasant.However, when fair spells have prevailedfollowing the disturbances, the ether hasbeen kinder on certain wavebands, andusually in the earlier hours of the night ithas been possible to tune in distant trans-missions without experiencing too dis-turbing a background.

On these occasions channels between16 and 30 metres have been, by far, thebest, and it is on this somewhat restrictedband that most stations have been loggedbefore midnight. In the early hours ofthe morning- it' is fairly safe to turn towavelengths above 40 metre's, and on somedays interesting captures were made.Sydney (N.S.W.)`

For the months of July and Augustslight alterations have been made in thetime -table of VK2ME, Sydney (N.S.W.),and you would do well to make a note ofthem. Broadea,sts now take place laetweenB.S.T. 06.00-08.00 10.30-14.30 ; and from17.30-19.30 every Sunday. In.my case it isthe first of these only which is well heard,although occasionally the last transmissionhas provided signals loud enough to permitidentification, but of no programme value.

From Paris comes the news that apowerful short-wave station - has beenerected at Homs, which is situated to thenorth-west of Beyrouth in the FrenchLevant, and.that we may shortly hear testsof speech and music. So far, excludingthe 13eyrouth-Kholde commercial stations,I have not been able to trace any, trans-mitter in official lists destined to the broad-cast of radio programmes from this region.

,ZeesenListeners who have opportunities of

turning to their short-wave receivers in themorning hours will find that two of the

I FROM THE LISTENING POST I

most powerful transmissions on the 'ether-are those provided by the Zeesen stationsDJQ (19.63 m.-15,280 kc/s) and DJB,(19.74 m.-15,200 kc/s). They may beheard at excellent loud -speaker strengthfrom the moment they come on the air atB.S.T. 09.55 until they close down atB.S.T. 14.00. During these broadcasts

RECORD

which are mainly intended for SouthernAsia,- some excellent concerts are given.A relay of the same prograinme 'is alsocarried out by DJN on 31.45 m. (9,540 kc/s).Later, from B.S.T. 14.05 until 17.00, DJEon 16.89 in. (11,760 ke/s) joins, iii withDJA on 31.38 m. (95.60 kc/s), and a kindof " Letter Box " with verbal replies tocorrespondents through the mike] to, listen-ers in the. Far East, is one of the regularfeatures of the programme. The Germanannouncer must be congratulated on his re-markable knowledge of the English language.MAKING.

MkVVVrkWWM:V:',WliS.: aZ,VW

Artur Schnabel and the B.B.C. Symphony Orchestra, conducted by Adrian Boult, are here seenmaking records in the His Master's Voice Studios,

PRACTICAL I AND, AMATEUR WIRELESS 507.August 1st/4936

avelengBad News for Croonersj EXTRACT the following from

the dignified columns of theChildren's Newspaper :-

" These miserable crooners, andall the people who make the...,airhideous with crude and barbarousnoises, are in danger ; there is aDaniel coming to judgment at Broad-casting House.

" He is Dr. R. S. Thatcher, Harrow'sDirector of Music, who has resignedhis distinguished post there to become

Dust on the aerial.

Deputy Director of Musk to theB.B.C.

" Many fine musicians are alreadyin the service of broadcasting, butthey pitilessly deliver us for long spellseach day and evening to perform-ances which, if attempted in thestreets a few years ago, might havebrought the perpetrators to the policecourt as public nuisances. For themodern style is exactly that of thebegging street -singer, gobbling, scoop-ing, out of tune, incapable of phrasingor of voice production.

" If any school child sang as thesecrooners do, howling, moaning, whin-ing, mispionouncing words, affectinga horrible twang, offending everycanon observed by teachers of music,the child would be forbidden to singat all ; yet the lowest depths of vocaldegradation find sanctuary in the B.B.C.studios.

" But our spirits rise. Dr. Thatcherhas as profound a loathing of theseatrocities as we have, and has ex-pressed himself in such terms asshould suggest to B.B.C. crooners,All hope abandon, ye who enter

here.' "We shall see exactly to what effect

Dr. Thatcher operates. I have said allI want to say about crooners and Iwould not dream of repeating thatI think they are crazy, half-witted,

By thermion

tintinnabulating, ululatory sob -voicednitwits, and like a flock of third-ratesheep. ' Nor shall I repeat whatI think of 'those who employ them.Watch any smug -faced -crooner smil-ing as he delivers his tosh-probablylaughing up his sleeve at the publicwho can applaud such drivel.

American SetsI HAVE received a further letter

on this subject from J. W. L.,of Llandudno :-

" What I have heard and readabout ' American Sets' is that theirperformance and selectivity is amaz-ing. ,Just to show, here is a cuttingabout the selectivity of a well-knownAmerican receiver : . . . here inChicago it can separate two of theworld's most powerful broadcastingstations, namely, WGN Chicago,50,00o watts, and WLW Cincinnati500,000 watts, and bring in WORNewark, 50,000 watts, with no inter-ference from WGN or WLW. Noother receiver in the world offers ahigher degree of selectivity. . .

Now the questions I have beenasked are :-

. " Why don't we in England makesets with 24 to 36 valves ?

" Why don't we have amazingselectivity ? '

" ' Why don't we in our sets havean output of 35 to 5o watts ? '

" Well, my answer is, British radioengineers can do this, but thelistener in this country does not wantto pay big prices for his entertain-ment, and not mentioning the amountof electricity such sets will consume.

" Perhaps, dear Thermion, youcould plonk a few words in yourarticle sometime about these ' Ameri-can Sets,' and perhaps more will' Buy British,' or should I say,

Construct British" P. and A.' Sets. "This reader hits the nail on the

head. The American public differsfrom the English. Our race was oldbefore theirs was born, and theirtastes are where ours were 500 yearsago. They like aborigine music ;they like to exalt Harlem ; theirtastes are simple and easily satisfied ;

what suits America does not suitEngland. Fortunately, there are afew intelligent Englishmen left whoknow what's what.`

Black MagicAY back in the dim dark

ages of 1922 a friend ofmine, who was considered quite aMarconi in his _district, persistedthat the crackles and spits whichwe now call atmospherics were dueto tiny particles of dust bombardingthe aerial. His friends sat round,mouths aghast, eyes agog, nostrilsdistended, ears quivering, and goggledat him. Sounds ridiculous, farcical,laughable, side-splitting, ludicroustheory, don't you think ? Or don'tyou ? It will be interesting to knowwhat this same expert says aboutatmospherics to -day. We shall belaughing in ten years' time at muchof what is considered sound practiceto -day. The theory of the etherhas never satisfied me, although ithappens to fit in. I am not at allsure about the skip effect and fading.I can't contradict because I have nota better theory. I don't like tobelieve that the earth is round,although everything indicates thatit is. Still,- we like to look back onthese queer notions as part of thegood old days.

Crystals on velvet.

The Good Old DaysAND talking of good old days,

do you remember the colossalprices we were asked to pay forcomponents ? Cardboard tubes with16 S.W.G. wound on, 17s. 6d.,earphones £2 2S. a pair' crystalsanything up to 5s. 6d. Can yourecall the smashing advertisementfor these latter ? Crystals in boxes,crystals so valuable that they re-posed on velvet ; crystals in caskets,crystals on velvet cushions. Special

508 PRACTICAL AND AMATEUR WIRELESS August 1st, -1936

cat whiskers made of gold wire at3s. gd. per inch. What a- pedigree -they all had. Experience and ex-

-Tense are almost synonymous terms,and once you have gained experienceyou find it difficult to give away.

Great SnakesONE of the technical boys, on this

paper is a camping fiend, and. took. out..the Midge Portable. withhim the other week -end. He riggedup the tent, turned on the radio,spread the cloth, and proceeded tokill the fatted. calf; only' to discoverthat he had not any milk (thatwouldn't worry me, I prefer a cork-screw). On returning from the farmhe found an adder sitting comfortablybut inquisitively by the radio listen-ing to some silky -voiced crooner.Snakes, as everyone knows, can becharmed with music, so this seemsto -be a complimerit to the Midge.only: Needless to say, great -dubietyexists amongst the staff as to whethertheir colleague had really gone formilk.

Too -too Modern SetsFOR my sins the other day I

had to go to tea with some ofmy relations, who proudly exposedtheir new radio set to my view.They said it was " just too modern,don't yoti think ? " I did think, and

Snakes are charmed.

to save further argument I. simplysaid " Yes." It was a modernist'snightmare-constructed in almostwhite wood with bands of chromiumplate sprinkled at angles. As therest of their furniture was mahoganyof the -1912 vintage, the combinedeffect was not too -too harmonious.It's this sort of thing that gets radioa bad name.

It is an unwritten law in the fur-nishing trades that you should notmix your woods, and nothing is morebizarre than bird's-eye maple in con-tiguity with walnut, mahogany,. andoak. A' radio set should be chosen totone with the rest 'of the furniture 'asfar as the colour' is concerned,although it is practically impossibleto select the receiver to match the style.

- Very few manufacturers arc makingreceivers which will blend with a Jaco-

-bean, Tudor or Queen Anne style.

Ultra-S.W. ReceptionTHE receiver sectidn- used for reception

of -pictures in the television appara-must be uapable of Passing a -very"wide

band of frequencies, " and therefore theintermediate -frequency amplifier must be:specially designed for thi.S. pUrpose-itmust.be timed to 'a much higher frequency;

; than the normal amplifier used -in broad-:cast receivers. The -sound accompani-ment of the picture can be 'picked uP1

;without using this epedial high -frequency t! I.F. amplifier, however, and if a frequency-changing valve can be obtained that will:

I function satisfactorily on wavelengthsbetween 5 and 9 metres the intermediate-

; frequency amplifier normally associatedwith sound receivers may be used.

U.S. ConverterA S in the case of 12 to 60 -metre recep-

tion, a converter may be used, :coupled to the medium -long -wave re-ceiver and thereby forming an ultra -short -1

; wave superhet. A converter of this typemust be very carefully constructed,however ; the frequency -changing valvemust be carefully -chosen, and the leads

t to the tuning condenser and coil must be; kept very short-it is advisable to mountI the coil on the condenser. Some fre- Iquency-changers will not function belowabout 15 metres, and when they are used ;in ultra -short-wave sets a triode valve has

; to be employed in conjunction with themin order to ensure efficient frequency-changing. Mains valves are generallymore efficient than their battery cminter-parts and satisfactory results can beobtained without the additional triode'

I if a modern mains changer is employed.

Correct Ganging; jT is often fount that accurate ganging1 I at all points on the tuning scalecannot be obtained when' cheap coils ofdoubtful make are used. This is generallydue to the coils not having the sameinductance, and the addition of a few turns ;to a canned coil is usually a somewhat

;difficult task. The best method of over-coming a defect of this type is to fit asmall 'variable trimmer condenser acrossthe aerial tuning condenser-the fixed i

! vanes of the trimmer to the fixed vanes ofthe tuning condenser and the moving;vanes of the former 'to the moving vanes

I of the latter. This extra condenser can !; be mounted on the chassis with its spindle; protruding through the front panel sothat it can be operated in conjunction

; with the main tuning control. An alter -T.method is to sulistitute a tuning f

drive having a variable concentric trimmer iattached for the straight drive in use. IThis type of drive -trimmer combinationis very useful when it is particularly I

: desired not to interfere with_ the ption of the Controls alreadyl disuse. The ;Use of an' extra trimmer is 'sometimesadvantageous even when reasonably well ;

; matched coils are: employed, as operation! of the extra condenser often helps tocut out an interfering station either by

i bringing the' two tuned circuits exactlyinto step,. or, in some eases by slightlydetuning the circuit to which the trimineris attached. " _

Of course, the bright young thingswho like to furnish in the ultra-modern style have no difficulty at all.They can select a set of almostsurrealist appearance, such is thecrazy tendency of modern times. Ifyou can't sing you can make moneyas a crooner, if you can't draw youmake a few daubs reminiscent of achild's" first efforts with a box ofcrayons and become a surrealiit, andmy readers may retort if you cannotwrite you become a radio journalist.I thought I would make this crackmyself to , save my splenetic corre-spondents from doing so.

Cycle RadioTHIS from E. R. (Royston)

" I'm 'very interested, in thesubject of cycle -radio, and I intend totry it myself. The idea of mountingthe set on the handlebars is feasible,but has Mr. E. Hurran (his letterwas published in a recent issue ofPRACTICAL. AND AMATEUR WIRELESS)found a loss in the leads to theaccumulator? I should think thatthere is a loss which caused a goodreduction of signal strength.

" Now about the suggestedReaders' League.' I am, as are

thousands more, interested in wirelessas- a hobby; it would be a very fineidea and should be launched as soonas possible. There is no club roundhere, and that's where a league would

Too -too modern set.

come in. We could swop experiencesand ideas, and thus gain some first-class knowledge of an interestingsubject.

" I agree with. E. A. Elliott (Hert-ford), and think that you should be

president' of the league.: But what'sit matter about a badge for you ?Crooners give me a pain in the neckand they ought to be punished bymaking them stick a few hours of

crooning.' Are we becomingAmericanised in jazz now ? One ofour leading dance band leaders wentto U.S.A. and came back with awfultunes, which are the craze of America.Good old Thermion, keep at 'em.Well, here's the best of luck toPRACTICAL AND AMATEUR WIRELESS,and may you live Many more years toentertain us with your views on wire-less and radio entertainment."

August 1st, 1936 PRACTICAL AND AMATEUR WIRELESS

A PAGE OF PRACTICAL HINTS

Combined Lead-in and EarthingSwitch,THE accompanying sketch shows how

the conventional type of ebonitelead-in tube can be readily modified toform an efficient earthing switch bymeans of which the aerial is disconnectedfrom the set and earthed without having togo outside the house.. The device has theadvantage of maintaining its insulationin the wettest weather. The ebonite tubeis cut to the length required and two ofeach of the parts shown are then madefrom strip brass or phosphor bronze of a

fairly stout gauge. Thecircular clips should bemade a trifle smallerthan the tube, so thatwhen the screw istightened there is no

MADE FROMHARD BRASS

STRIP 3/iXske

A weatherproof combined lead-in and earthingswitch.

possibility of movement. The protectivehood on -the outside end of the lead-intube is' a bakelite picnic cup with thehandle sawn off, and having a hole drilledin the bottom. When assembled, the switchshould have about half an inch movement,and 04 small, knob should be screwed to- theinside end for operating purposes.-D.BESSANT (Mitcham).

A Useful DodgeVVIIIERE small articles such as nuts,VV bolts and screws have to be picked

up out of awkward corners, the dodgeillustrated in the accompanying sketchwill be found useful. A strong rubber bandis simply placed round the shoulders of apair of pliers, as shown, to act as a spring.The pliers are opened in the ordinary wayand the jaws placed over the article to belifted, which remains gripped in the plierswhen the pressure of the hand is released.-K. E. GAYLAND (Weybridge).

Adapting a pair of pliers for picking upartides from awkward corners.

I

THAT DODGE OF. YOURS!Every Reader of " PRACTICAL AND

AMATEUR WIRELESS " must haveoriginated some little dodge which wouldinterest other readers. Why not pass it onto us ? We pay Z1.10-0 for the best wrinklesubmitted, and for every other item publishedon this page we will pay half -a -guinea. Turnthat idea of yours to account by sending itin to us addressed to the Editor, " PRAC-TICAL AND AMATEUR WIRELESS,"George Newnes Ltd., 8-11, SouthamptonStreet, Strand, W.C.2. Put your name andaddress on every item. Please note that everynotion sent in must be original. Markenvelopes " Radio Wrinkles.', Do NOTenclose Queries with your Wrinkle.

A Sensitive GalvanometerTHE accompanying sketch shows a

sensitive centre -zero type galvano-meter, which is easy to make and yet isnot of too delicate construction. Theessentials can be clearly seen in the diagram.The coil is wound from an old transformer,and the gauge and amount of wire is notcritical ; but, of course, the greater numberof turns the more sensitive the instrumentis. In some cases the transformer coilsmay be used without re -winding on alarger former, but usually the hole in thecentre is too small to fit the suspendedmagnet assembly. The magnets are piecesof needle which have been magnetised andpushed through the cork cube in the sameplane as that of the coil.

A paper sheet is glued to the needle toprevent it swinging too much. For bestresults the paper should be as large as

Tam's

LEAD BALANCEWE G141.

COIL

Genera! view of a sensitive galvanometer,and details of coil and magnet suspensicn.

possible, and should have as little clearanceas practicable between it and the top andbottom of the case.

The needle will normally come to restin an E/W position, but it may bebrought to the zero- mark in any positionby the use of a small magnet moved aboutthe top of the box just over .the suspendedmagnet. With suitable adjustment of thecontrol magnet this instrument can beused as a visual tuning indicator. Thissimple instrument will give a full

small deflection with .04 m/A.-R. B. -MITCH(Liverpool).

509

A Changeable Coil -former AssemblyTHE simplicity of this idea is evident

on referring to the illustration, andthe only accuracy necessitated on the partof the constructoris in the maskingout for drilling.,The whole as-sembly comprisesone ebonite tube15/16ths-in. (out-side diameter) ofa length to suitthe design of coil(the former usedin this instancew a s obtainedfrom an old powerresistor) ; a chas-sis -mountingvalveholder (cera-mic or bakelite) ;four wander plugs,with screws andnuts as shown,and four insulat-ing washers.

After securingthe wander -plugcasings to thechassis, and A method of arranging a

changeable coil -formerinsulating withassembly'-washers under-

neath, the plugs should be screwedhome sufficiently- tight- to make contact

with the fixing screw heads. Theformer and valveholder assemblyare worked on to the plugs, wiringbeing effected from the screw, asshown. To make the former secure,place a screwdriver between eachpair of valve -leg sockets, and priseslightly, then work the former intoposition.-W. R. HOBBS (Ilford).

Dip Soldering

WHERE a number of smallparts have to be soldered,

instead of using the soldering ironthe work may be more speedilyexecuted by melting a quantity ofsolder over the gas ring, with the

flame turned low, using plenty of Fluxiteto prevent the solder oxidising. The partscan then readily be tinned and held together.Use two pairs of tweezers and, after dip-ping, hold the parts together until thesolder has chilled off. This method is veryeffective when soldering tabs to fine wires,as an iron tends to destroy the strength ofthe wire.

LATHE -WORK FORAMATEURS

byF. J. C A MM

1/- or 1/2 by post fromGeo. Newnes, Ltd., 8-11, Southampton Street,

Strand, W.C.2.


August 1a, 1936. Vol. 3. No. 13.

D.C. LightACERTAIN amount of confusion still

seems to exist with reference to theexpression " D.C. light," which is

now used so often when information ispublished concerning the forthcoming high -definition television transmissions. Itconcerns the, relative degree of lighting usedin the studio, or when televising exteriorscenes. The form taken by the signal to betransmitted by each company at theAlexandra Palace is known to have a"black " carrier level of 30 per cent. forMarconi-E.M.I. and 40 per cent. for Baird's,and all carrier amplitudes below thesefigures are concerned only with the synchronising pulses which for distinction aresaid to occur in the " blacker than black "region. When the carrier wave of theultra -short-wave radio transmitting stationis on the air with L.F. and H.F. syn-chronising pulses only, the signal remains atthis constant level. As soon as the picturecomes on, however, the amplitude level ofthe carrier will rise into the region whichgives a total gradation of from black towhite. The continuous variations of thecarrier level correspond to the degrees oflight and shade in the televised picture,which, when retranslated at the receivingend, give the gradation that conveys to theeye the picture or scene which is transmitted.To quote an easily assimilated analogy thiscan be likened to the varying current in theoutput circuit of a standard radio set,which variation is converted by the loud-speaker into intelligible sound. In theoutput -valve circuit of the set, however,there is a steady ourrent flowing, andalthough it has no real significance as faras the final sound is concerned, the presenceof this steady state is well known.

Coming to any studio scene or outdoorshot, however, there is a steady state ofD.C. lighting effect present-namely, thedegree of overall lighting which is employedto illuminate the scene or subject. When weview scenes naturally by .the eye, or watchcinema pictures, we can appreciate im-mediately whether the steady state is oneof brilliant sunshine, artificial illumination,twilight and so on. To complete thepictorial effect of the televised pictures thisoverall lighting must be incorporated insome way in the signal, otherwise theaverage brilliance of the scene will remainunaltered from the level set by the receiveruser at the beginning of the transmission.This is what happened in the earlier days oflow -definition televisioh, but with theadvent of high -definition images the situa-tion is changed completely. Both com-panies have agreed that the picture bright-ness component will be transmitted as anamplitude modulation. In this way themean brightness of the D.C. light value ofthe picture is made implicit in the signal,or, in other words, there will not be any fixedvalue for the average carrier as this will varyaccording to the measure of lighting presentin the transmitted picture. This adds con-siderably to the quality of the picture, butunless precautions are taken at the receivingend it will be lost. The average thermionicvalve amplifier cuts off any D.C. componentdue to the presence of the interstage-coupling condenser. If the coupling ar-

rangement, however, is designed to havea large time constant, then this D.C. com-ponent will be operative, and the full beautyof the picture appreciated.

Frequency Band InvolvedWould-be constructors of ultra -short-

wave radio sets for tuning, in the radiatedtelevision signals so that after amplificationthey can be made. to modulate the picture -reproducing device, seem to display a littleuncertainty as to the frequency bandinvolved in the vision signal. Two separatestandards are employed according to which

elements, the frequency involved in the.Modulation is half this-namely, 960,000,since one complete cycle "corresponds to a'black and a white square. Roughly speak-ing, it is safe to say that the modulationfrequency under these conditions is onemegacycle, or the sideband involved in theradiated carrier wave is two megacycles(band -width is always twice the maximumfrequency). On the other hand, if thescanning equipment is worked to the 'limitso that the scanning aperture or spot justfails to differentiate between separate blackand white elements, this condition will bemet by reducing the length of each elementin the direction of line scan to half theprevious side. The maximum modulationfrequency is then doubled to 2 megacycles,and the carrier sideband width to 4 mega-;cycles, and this is the condition which willoperate in practice. To take full advantage:of the radiated picture under the initialstandard mentioned, the vision radioreceiver must be capable of accepting and

amplifying a maximum modu-lation frequency of 2 mega

This is the most difficult operation in the making of cathode-raytubes. Here you see an expert glass-blower in the televisionlaboratories of the German Post Office in Berlin making the"front of the tube!! as flat as possible. This portion of the tubelater is to hold the screen, and it requires very special skill to

produce an even surface.

company's equipment is being used (alter-nate weeks of use is the B.B.C.'s proposalat present, but this may be modified afterexperience when the service starts). In onetransmission the definition is one of 240line horizontal dissection repeated at25 frames (and pictures) per second, thedimensions of the picture having a ratioof 4 horizontal to 3 vertical. Assumingequal definition both horizontally andvertically, therefore, the total number oftiny square elements in the picture isobviously 240 x 240 x , that is 76,800.The total number of elements scanned inone second, therefore, is this figure multi-plied by 25, that is 1,920,000. Takinga limiting case of alternate black and white

cycles without any amplitudedistortion. That is to say,'the characteristic of the am-plifier must be horizontalIdecibels plotted against fre-quency) up to the full 2megaCycles. This may seema very arduous task afterthe standard of quality soundamplifiers, which were ratedas first class if they passed amodulation frequency of 10kilocycles, but it can be ac-complished if a proper -studyis made of the new amplifiertechnique.

With the other picturestandard, line definition is405, complete pictures 25 andpicture dimensions five tofour. Calculating on thesame basis as previously, thetotal elements in each pictumfor equal definition horizon-tally and vertically is 405 x405 x 1, that is 205,031, andthe modulation frequency be-comes 2,562,900 (band widthis twice this figure). Work-ing to the limit, however, sothat the scanner just fails todifferentiate between blackand white, the modulationfrequency is doubled, and forall practical purposes can betaken as 5 megacycles, afigure more than twice thatquoted for the other picturestandard. Readers will ap-preciate from these calcula-tions, therefore, that visionset design and layout are twofactors which merit very

careful attention if full advantage is to betaken of the radiated picture detail.

Not in OppositionA representative of four hundred news-

papers told the United States Federal Com-munications Commission that he did notbelieve that either television or facsimilebroadcasting could in any way be regardedas an opposition to newspapers. Mr. Leinertgave details of a television system capableof producing full-size theatre screen pictures(24ft. by 18ft.)without any time delay factor.Similar principles were being developed toenable home television sets to give a pictureabout 3ft. wide, and yet sell for a sum notexceeding fifty pounds.

August 1st, 1936 PRACTICAL' AND AMATEUR ' WIRELESS 511

uality CZ. PCUitSBrief Descriptions are Given of Various Circuit Arrangements of ComparativelySimple Type which can be used when Good Reproduction is Desired

at a Modest Cost

THE average keen constructor has long,

since learned that, for real andlasting enjoyment of broadcast pro-

grammes, good -quality reception is essential.His chief difficulty is, however, that heis frequently uncertain as -to the method ofensuring such reproduction without goingto considerable expense. He knows thatan expensive amplifier with push-pull,paraphase or Duophase output would fulfilhis requirements-but he also knows thathis pocket is not deep enough for such

.0005 tifta

i>Z> r 0042Afro

0005PAW

NEC Cs/C,

0PU.0

25 MF05Fig. 1.-A simple Det.-L.F. "quality" circuit fo

can b

HL./320

Oj AlF. O.

ma

50042 50011

coil (of any good make) is used in the inputcircuit, and this feeds into a leaky -griddetector. This is coupled to the secondvalve by means of a resistance -capacitynetwork, whilst coupling between thesecond valve and the output pentode is, ofthe same type. Despite the fact that R.C.coupling is not as popular as it used to be,it is still better than any other when com-plete simplicity and absence of " snags,"combined with cheapness, are the firstconsiderations. The two anode -coupling

/0,000 .S2

luxuries. In this article, therefore; it isnot proposed to deal with circuit arrange-ments which can be considered as " thelast word," but rather with comparativelysimple ones which can be tried without anyconsiderable expenditure.

Mains Operation PreferredA few of the main points which have to

be considered with regard -to qualityreproduction were outlined in the " Begin-ners' Supplement " last week, so it will besufficient to proceed from the 'pOint atwhich that explanation was 09n -chided.In order to obtain reception which. is morethan just " good," a mains-Ofieratedreceiver is practically essential, althoughthere are exceptions, as will be explainedlater. The average constructor does notwant to be troubled with unusual andapparently complicated circuits, but wouldgenerally prefer to employ an arrangementwhich is as nearly as possible similar tothose he has used before ; the circuit shownin Fig. 1 is a typical example of what ismeant. This circuit is the same in principleas the Det.-two L.F. circuit which has beenpopular for many years, but it is intendedfor really good reproduction of a few pro-grammes. Selectivity is not a strong fea-titre ; long range is not intended ; but goodreproduction at ample volume is assured.

Detector -Two L.F.It will be seen that the circuit is intended

for universal mains working and thatstandard triode and pentode valves areincorporated. A simple two -circuit tuning

therefore shown in broken lines ; if theseconnections are used care should be takento use the smallest amount of reactionwhich suffices to sharpen tuning and givesufficient input to the detector. As tothe power -supply system, this is as simpleas possible, and an H.T.12 metal rectifieris used for half -wave rectification, whilsta Phillips type C.1 barretter is used asan-autontic series resistance in the heatercircuit ; the set can be used on any main -4having a voltage between 160 and 300.

Values of the principal components areindicated, and it should be added that thefirst two valves are Mazda, and the outputvalve a Cossor. All resistances can be ofthe 1 -watt type, tie smoothing chokeshould have a resistance of not more than500 ohms, and the fixed condensers shouldbe for not less than 300 volts working.

Push-pullIt would be possible to argue for a long

time on the relative merits of the circuitshown in Fig. 1 and that in Fig. 2. Thelatter also employs three valves, but theseare arranged as a detector valve followed bya push-pull stage. The output is notvastly different, but the second circuit israther more costly and would perhaps notbe considered quite as simple by con-structors of modest experience. Thesecond circuit is, however, shown in A.C.form, and provides an interesting alterna-tive. One of the chief advantages of theFig. 1 arrangement is that it provides arather greater degree of amplification inspite of the similar maximum output. Forthat -reason it can generally be used with alower setting of reaction, and is moreeffective when the nearest transmitter ismore than, say, 25 miles away. Again,the values of components are marked on thediagram, and further explanation need notbe given.

There are many designers who considerthat, even for a local -station " quality"set, a stage of high -frequency amplificationis to be preferred. The pros and cons areapt to become rather involved, but the


/5.000.12 /00

iRstREsrmom CH

30.H

r universal mains working. An output of 2 wattse obtained.

resistances have a value -rather lower thanthe theoretically -correct one, but this hasbeen purposely arranged so that the anodevoltage is cut down as little as possible.A pentode is' mot always considereddesirable in a quality set, but it is certainlythe best in a universal receiver: In anycase, if reproduction is rather on the shrillside it is a simple matter to connect a tonepontrol between the anode of the outputvalve and earth.

Reaction is not strictly desirable in acircuit of this nature, and connections are

VALVES:VI- 41 MHL-CossorV2- PX4-0sramV3- PX4-OsramV4- 442 BU-Cossor

R5 250-C1AAA

C5.0002.mfd

8

Cl-0005m

R3ipoon.

Fig 2.--Aaother three -valve " circuit-this time for A.C.--with push-pull output.

512 PRACTICAL AND AMATEUR WIRELESS August 1st, 193 6(Continued from previous page)

constructor who does not object to the slightextra complication of a receiver having aH.F. stage is advised to adopt it. Oneimportant reason for this is that it ensuresthat the detector valve can be fully loaded.As a result of this it might be possible touse rather less low -frequency amplificationto obtain the same output, which in turnmeans that the L.F. side is simplified. Onthe other hand, it is probably true to saythat-contrary to what is generally thought-a greater amount of distortion takes placein the H.F. than in the L.F. stage of, mosthome -constructed receivers, unless builtaccording to a complete published design.

Using H.F.Another advantage of using H.F. ampli-

fication is that it can be followed by a diodedetector. It is rarely satisfactory to connecta diode directly to the input tuning circuitsince it produces too much damping andcannot be properly loaded. And it is safeto say that, in the hands of the averageconstructor, a diode gives better qualitythan a triode, even when the latter is usedas a power -grid detector. Yet anotherpoint in favour of the H.F. stage is that itentirely obviates the need for reaction onstations up to 100 miles or so, and oftenmakes possible the good reception of trans-mission over much greater distances. , Asimple, though very satisfactory circuitcomprising an H.F.-pentode H.F. amplifier,a diode detector and two stages of L.F.amplification is given in Fig. 3. In thiscase the set is for A.C. operation, and itincludes a mains transformer giving anoutput of 500 volts at 120 mA this isnecessary in order to feed the Mazda PP5400 output triode, which takes a maximumanode voltage of 400. The other two valvesare Cossor, and the rectifier is a Cossor,type 460 BU, the output of which is 520volts at 120 mA. Actually, the maximumvoltage is not applied to the output valve,since a 2,500 -ohm loudspeaker field windingis used for smoothing purposes, but thismerely means that the valve is not worked" all out," which is an advantage.

Component values are indicated, theseapplying to the valves indicated. It will beunderstood that all smoothing and by-passcondensers must be designed for workingat not less than 600 volts ; the resistancesmay be of the 1 -watt type, excepting thatused for biassing the last valve, whichshould be a 2 -watt component. The outputvalve has a directly -heated filament, butthe other two are indirectly heated ;because of this it is most convenient toemploy a mains transformer with separate

/5.000(2

000/ MAD.. .0006-

/TAO.

L.T. windings, each rated at 4 volts andnot less than .2 amps.

Volume ControlInstead of using a variable -mu valve to

control the input and prevent overloadingon powerful signals, a differential condenseris used in the aerial circuit-a system whichhas previously been recommended in thesepages for " quality " receivers. An unusualand simple method is adopted for feedingthe screening grid of the H.F. pentode, forthe double -diode triode and its anodedecoupling resistance are used together asa fixed potentiometer. This circuit is

< T

the excellent quality which it gives, butthe connections shown in Fig. 4 makerepiciduction still better, and withoutdetracting from the remarkable performancewhich the set is known to give. It can beseen that the first L.F. valve is a Cossor215 P, and that it is connected to the outputvalve through a resistance -capacity couplingconsisting of a .01-mfd. condenser and a10,000 -ohm resistance. The output valve isa 230 XP,. which has a maximum un-,distorted output of 450 milliwatts and takesabout 16 mA when using 120 volts H.T.

In order to ensure the best possiblereproduction a slight degree of selectivity,

must be sacrificed

L_

oH.T+2

\C)/230 f?

6.8i>

1.1-6.8. -

Fig. 4.-Showing how the pentode in the £5 Superhet can be replaced by twotriodes in order to improve still further the quality of reproduction.

probably the best simple one that could bedevised for really high-class reproduction,but care should be taken in the choice ofthe low -frequency transformer. This shouldbe of the best quality obtainable, and shouldhave a step-up ratio of 1 : 2 or 1 : 3. Theprincipal objection is the high H.T. voltagerequired, but since standard componentscan be used, this need not introduce anycomplication.

Battery OperationIn the case of a battery set a circuit

similar to any of those described abovecould be used by employing suitable valves,but the output could not be expected toexceed about 1 watt-and even then theconsumption of H.T. current would be high.It is worth mentioning, however, that areceiver such as the £5 Superhet can easilybe converted into a good " quality "instrument simply by replacing the outputpentode by two triodes, as shown in Fig. 4.Those who have built this set can testify to

75.000 fl2,60042

4211A0 441F-0.0S

RAS/400

soot( a

A

oheroFig. 3.-An receiver circuit with diode detection and capable of over 4 watts output.

4.00012

/ tIFO as meas.

by tightening thecoupling betweenthe windings of theI.F. transformers ;even when this isdone the set tunesvery sharply andhas the same longrange of receptionas before the alter-ation. The " West-ector " is just asgood as a diodewhere " quality "is concerned, butis not generally tobe recommendedfor a " straight "set unless precededby a couple ofH.F. stages.

HERE and THEREMotor -Cycle ChampionshipsTHE Bank Holiday motor -cycle cham-

pionships at Donington Park, someeight miles from Derby, have now beenrecognised as Grand Prix Races. There'are over a hundred entries this year. Thedistance to be covered is one hundredmiles-about forty-five laps of the course,'which is the same, as for the Grand PrixRaces for cars. On August 3rd three'commentators- will be engaged for the'Midland relay, Graham Walker, VernonBrook and F. J. Moore. The two first arewell-known T.T. Race Commentators, while`Mr. Moore has done commentaries for thecrowds round the course at Donington Par.

Stories of Fifty Years AgoAFEATURE of the Midland Children's

Hour on August 3rd is an exchangeof stories of fifty years ago between atownsman and a countryman. The formeris Joe Gutteridge, the Black Countrybroadcaster ; and -the latter, Sam Ball, aShropshire gamekeeper.

Soviet ProgrammeAS mentioned in previous issues, the.

Soviet government has extended itsshort-wave programme service for listenersoverseas, and for this purpose has broughttwo new transmitters into action. MoscowRW96 on 19.76 m. (15,180 ice/s) gives anEnglish programme every Sunday atB.S.T. 18.30 and on 31.51 m. (9,520 kc/s),.a' daily broadcast from midnight to 02.00B.S.T. At other 'periods on the lowerchannel you will hear telephony as it islargely used for communication with otherstations in the U.S.S.R. You will recognise,the station by the announcer's reiteratedda-da (yes -yes) or niete (knee-ett-aye), whichis equivalent to our "- No.


SOUN ECOthe AMAT

AFEW years ago, home recordingcreated a considerable amount ofinterest amongst those who wished

to obtain a permanent or semi -permanentrecord of some particular vocal or musicalitem. Unfortunately, in spite of severalmanufacturers producing simple suitablepparatus, the interest did not last, and a

very interesting branch of acoustics-so

Fig. 1.-The standard gramophone record groovesas seen under a magnifying. glass.

closely allied to radio-more or less fadedaway so far as the amateur was concerned.The probable reason for this was certainimperfections and snags which were thenpresent, but, since its first- introduction,home recording has made wonderful pro-gress. There are, however, several pointsto be -watched, and unless due considerationis given to these items, the amateur record -

maker will become very disgusted with the"results he obtains.

The purpose of this article is to stress thepoints to be watched and explain theelementary principles of record -making, soit is hoped that those new to this veryinteresting hobby will be able to avoid someof the pitfalls which can prove so annoyingand disheartening.

Record -makingIt can be said that the grooves or tracks

on a blank record can be shaped to representvibrations corresponding to sounds in twoways, one of which is known as the "hill-and -dale " system, and the other, the" lateral " method.

Both systems possess certain definiteadvantages, but for reasons which do notconcern this article, the "lateral" systemwill be considered as the one most suitablefor home recording.

If a record-using the lateral system-is examined under a microscope, it will beseen that the grooves which form the spiraltrack, are not smooth -sided channels asthey appear -to the naked eye. They have,actually, a zig-zag formation, as depictedin Fig. 1, which represents a plan view ofsome of the grooves-but more about thatlater.

The " hill -and -dale " method differssow the above, inasmuch that no lateralnovement of the needle is produced, thedg-zag line across the record being replaced)37 one at right -angles to the surface of the'ecord. This can be more readily under-tood if we think of the grooves in termsif the name given to the method, andrefero Fig. 2, which shows a side view of a

DING forELJ

y L. Ormond Sparkssection of a groove. It will be seen thatthe bottom of the groove is no longerlevel ; the path of the needle being likea series of minute hills and dales, and itis> worth noting, at this point, that thedepth of the " dales " does not affect thewidth of the groove or track.

In this Article the ElementaryPrinciples of Record - makingare Explained, and Various Points -1,1

to be Watched. are Stressed

It is obvious that the stylus bar of asound -box or pick-up will vibrate in ato-and-fro manner (Fig. 3) when the needleis following a lateral track, the diaphragmbeing at right -angles to the record surface,and that the maximum movement will begoverned by the distance between grooves,i.e., the thickness of the walls. Thisgoverning factor has a great effect on thefrequency response obtainable from arecord using the lateral system ; for

S(/RFRCE-y (TRIICK

WRX CORE OF RECORD),

Fig. 2.-The " hill -and -dale" method of recordmaking.

example, the large zig-zag represents alow -frequency note, and it is possible that,say, a 100 -cycle note would produce a trackwhich would occupy the total permissiblewidth of the groove. Therefore, any notelower than that frequency would have tobe attenuated or, in other words, restricted,otherwise the walls would be broken downand the spiral track ruined.

With the "hill -and -dale " method, theneedle is given an " up-and-down " motion

3.-The ordinary sound -box is operated asshown here.

(Fig. 4), the diaphragm being fixed parallelto the record surface; therefore the low-frequency limitations do not apply, as thedepth of the " dale" corresponding tolow note does not affect, as mentionedearlier, the width of the groove.

How the Track is MadeWhen records are made on a commercial

basis, and many thousands have to beproduced of one recording, it is usual forthe following procedure to be adopted.

The sound to be recorded is convertedinto electrical impulses by suitably -designedand controlled microphones, whose outputis amplified by specially.eorrected amplifiers'until sufficient power is obtained to operatewhat is known as the " cutting head.",For 'simplicity, the " cutt ng head " canbe likened to a pick-up whose operation isreversed, that is, instead of producingelectrical currents by the vibration of- itsneedle arrangement, it is made to producevibrations by supplying it with electricalpower like, one might say, a loudspeaker.The cutting head is connected to a mechan-ical drive which casues it to follow apredetermined spiral path across a disc of

-specially-prepared wax, the cutting needleengraving or cutting out the minute zig-zagtrack which forms the mechanical/electricalequivalent of the sound being, recorded.

When the recording is finished, the waxrecord is treated with a super,fine con-,ducting medium-something like graphite--

MOVEMENT -

D/APHRAGM

SAPPHIRE OR 3,DIAMOND POINT

MOVEMENTFig. 4.-This shows holt) the diaphragm is operated

in the" hill -and -dale system.

and then immersed in a plating bath untila strong metal coating is deposited on thetreated wax. This metal " positive'-'.counterpart is used to produce " negative ".1metal plates which 'form-for want of abetter name-a die to press out a corn-'position into the familiar black discs. This'is not the final stage, as the discs have to tbe given the finishing touches, their edgestrued up and carefully examined for themost minute imperfections.

Home RecordingSo much for the outline of the commercial

process ; now let us see what is necessary,for the amateur record -maker, as it isobviously impossible for such complicatedmethods to be used in the home.

To overcome the problem of the wax disc,recording " blanks have been made from'aluminium, and while these have provedquite -Satisfactory from the recording pointof view, they possess certain undesirablefeatures when it comes to reproducing.However, they offer quite a good basiswith which to start experiments but, if thematter is going to be tackled seriously, it

- .51.4 PRACTICAL AND AMATEUR WIRELESS August 1st, 1936

would be advisable to use one of the more,modern processes.

Aluminium blanks should be cut with asapphire cutter, and it is essential to usefibre trailer "needles for replaying other-wise the useful life of the record is veryshort, say, six playings only with steelneedles. Fibre needles are, of course, verysatisfactory as regards quality and absenceof surface noises, the only drawback beingthat they wear very rapidly, and once thecontact surface becomes worn or distorted,objectionable snags are introduced.

. While the term cutting has been used,this is not quite accurate when consideringaluminium blanks, as the surface is actuallyindented and not cut like other substances.However, quite good results can be obtained,and the method has the advantage of beingvery cheap.

Before any recording can be considered,it is essential that some mechanical deviceis provided to cause the cutter head totraverse the record "from edge to centre, asthe blanks are free of all tracks or grooves.Stich devices are known as " tracking "or " traversing " mechanisms, and theyusually consist of a threaded rod, which isoperated from the turntable spindle, andso arranged that it controls the movementof the cutter head carrier. Fig. 5 showsthe fundamental principle where " A "represents the drive fastened to the turn-table spindle, and, " B " the simple gearsto transmit the motion to the horizontalthreaded rod " C " which actuates thecutter carrier " D " _by means of thethreaded contact piece " E. The pitchor number of threads per inch of thethreaded rod 'plays a very important part,and it is absolutely essential for it to be aprecision job, otherwise the distancebetween each groove will vary, the separat-ing walls will differ in thickness and a truespiral will not be formed.

With commercial recording, it is usualto operate at 100 grooves to an inch, butfor home purposes it is not advisable tocut more than, say, 80 to 90 per inch asthere is always the danger, unless a veryaccurate check is kept on the cutter headinput, of the cut of the low notes breakingdown the walls of the grooves and completelyspoiling the track.

It will be appreciated that to overcomethe drag imposed by the cutter-especiallywith aluminium blanks, and the load ofdriving the tracking mechanism, a power-ful motor is required, so particular atten-tion must be given to that item. As aguide, it should be noted that a single springor small double spring motor is not likelyto be satisfactory ; in fact, some of thesmall electric motors arc not capable ofdriving a 10 or 12 inch blank.

Motor speed is a very critical item anduse should be made of one of the manydevices for checking this, otherwise thewhole tempo and pitch of the recording willvary. To show how closely the questionof speed is studied in commercial recording,it is interesting to note that " gravity "or weight operated motors are used in manyof the studios.

One more item which calls for specialattention in recording, is the weight of thecutter head, or rather the actual weightimposed on the cutter. If the weight orload is too light, the cutter may wanderoff its track or jump clear on some of thelower frequencies. Most of the cutterhead carriers are fitted with an adjustablecounter balance which allows very accurateadjustment to be obtained.

Cutter HeadsAs the frequency response of a loud-

speaker depends on its design, ignoring for

the moment the inputso will the quality ofthe recording depend on the characteristicsof the cutter head. Therefore, it is no useproviding first-class gear if attention isnot given to this important item.

Special cutters can be secured from firmswhich specialise in this class of work or,on the other hand, any good make of electro-magnetic pick-up can be used, providingthe question of weight is considered, asmentioned above. Suitable cutting needlescan also be purchased, and, while they anbe made if so desired, it is really better toobtain them from the actual makers.

Power and FeedFor satisfactory results, the L.F. amplifier

feeding the cutter should have an undis-torted output of at least 3 watts, the out-put stage, for preference, being push-pull.If, however, this form of output circuit isnot employed, a choke filter circuit, oroutput transformer, should be used, thusprotecting the windings of the cutter headfrom D.C.. current, and removing anypossibility of L.F. instability.

The amplifier circuit should embody anefficient form of " high " and " low " notecontrol, to allow adectuatap adjustment tobe made to the overall frequency response.

mew'emuuuuuunuuuutuunuuiiaric

Fig. 5.-How correct tracking is obtained.

It may be necessary to attenuate the lowerfrequencies if the cutter input is too great,or if more than 80 'grooves per inch arecut.

The input circuit of the amplifier shouldbe arranged to suit the type of microphonein use, and, if possible, it is advisable tomake use of a mixer circuit to allowspeech and music or other combinations ofsounds to be blended as desired, as verypleasing and, incidentally, very professional,effects can be so produced. As regards the

microphone, any good make of " transversecurrent " will be quite satisfactory, althoughif a- moving -coil job is available, so muchthe better.

BlanksAs mentioned earlier, the aluminium

blanks are not too satisfactory if longrecord life is required, or if serious workis to be undertaken, therefore, it is wellworth while considering one of the moremodern methods, and while there areseveral processes now in being, I do notthink the amateur can do betterthan employthe system outlined below, which is handledby Messrs Musikon Ltd. They still employan aluminium blank, but only as a basefor a film or coating of a plastic substancevery similar to bakelite. The nature of thesubstance allows recording to be carriedout, in the normal manner, with asteel cutter, and owing to the nature of thesurface, very little drag is imposed on theturntable. After cutting, the record can,if so desired, be replayed immediately,but this is not recommended, as the surfaceis too soft and must be hardened beforeuse. The hardening process is carriedout by the simple process of placing theblank in an oven-maintained at a certainconstant temperature-for about threehours, after which a glass -hard surface isproduced which allows steel trailer needlesto be use.

The finished records have a remarkablefrequency response, very long life, andsurface noises are practically absent.

Important PointersWhichever system is used, never start

recording and run a blank right through,without having previously made a teststrip of t4 matter to be recorded. It isadvisable to keep one blank for this purpose,and run off a few grooves, under operatingconditions, to see if volume, speech or theplacing of the microphone is all right. 'Makequite sure than no external interference islikely to be introduced into the microphoneor amplifier circuits. Check up the timeto be taken by the item to be recorded, andthe time length of the blank, thus avoidingone finishing before the other. See that theinput to the microphone is constant or,better still, have headphones in circuit anila proper volume control. And last, butby no means least, keep your eye on thespeed of the motor.

A NEW TELIANISION "SETHE other day a newspaper stated that a

television service had at last started,but this was meant to refer to the bus

service which has now been inaugurated as aregular afternoon journey between Broad-casting House and Alexandra Park. Withthe constant delays which have accrued,and so prevented the radiation of picturesignals this sarcasm is perhaps excusable,but in suggesting dates for the initialservice the authorities failed to realise theamount of work which had to 'be accom-plished. Every effort is now being made toexpedite the work, and in spite of the air ofcomplete secrecy, which surrounds the in-stallation, at the summit of the steel latticemast engineers can be seen perched veryprecariously while putting into position theradial arms which ultimately will hold thespecially designed vision and sound aerials.Then it is known that the two large studioscan 'be sectionalised by means of curtainson " railways " so as to apportion the

VIC "backgrounds according to the size of thescene it is intended to televise. The controlengineers are above the studio floors, andanyone in that room can therefore see intothe studio and watch the actual scene.Equipment assembly is proceeding apace,while quite recently a section of the newtelevision staff paid a -visit to the AlexandraPalace in order to see the. film scanners inoperation. This was part of the course ofinstruction which they are undergoing inorder to become acclimatised to B.B.C.methods. No doubt' in August their workwill become more -specialised in relation totelevision itself. It is also learned thatphysical exercises will be featured in thetelevision programmes. Readers will nodoubt recall that this was quite a popularitem in the low -definition television pro-grammes, but the scope was rather limited.Using the present forms of direct pick-upscanners, however, far more detail will bepossible.


I M PRESSIONSON EH E. WAX II

ByI T. Onearm

Two Famous OrchestrasOF the lighter overtures, one of the

most popular is " The Merry Wivesof Windsor." It 'has been re-

corded this month by the Berlin Philharlmonic Orchestra, conducted by Dr. Karl_Bohm on H.M.V. DB 4444, a particularlyfine record.

The " Blue Danube " waltz is always afavourite with Strauss admirers, and theMinneapolis Symphony Orchestra has madean extremely good rendering of it on H.M.V.DB 2621.

From the FilmsJAMES MELTON, who appeals in the

film, " Stars over Broadivay," hasrecorded " Where Am I ? " (" Am I

in Heaven "), and " Carry Tile back to theLone Prairie" on H.M.V. B 8444. Both ofthese tunes are from the film.

Another new film, " Give us this night,"is represented by " Sweet Melody ofNight " and " My Love and I," which areattractively sung by Webster Booth onH.M.V. .B 8442.

Sam Browne sings " Melody from theSky," a popular tune from the, new colourfilm, " The Trail of the Lonesome Pine,"coupled with " Lost " on H.M.V. BD 351.

Musical Comedy SuccessesSOME of the best known musical comedy

successes are recalled in ""Medley of- Daly's Favourites," played by

Reginald Foort on the organ of the Para-mount Theatre, London. The number ofthe record is H.M.V. BD 352.

Derek Oldham sings two light numbers," A little love; a little kiss ' (" Un peud'amour "), and " Nocturne" (" Song ofLove ") on H.M.V. B 8446.

Two songs of totally different 'category,but which offer pleasing contrast, are sungby Stuart Robertson (baritone) on H.M.V.B 8445. The titles are-" Spanish Lady,"and " Limehouse Reach."

A New Toscanini RecordTWO brilliant recordings by Toscanini

and the New York PhilharmonicSymphony Orchestra appear inthis month's list. They are Gititter-

clammerung "-Dawn and Siegfried'sRhine Journey, and " Lohengrin "--Pre-lude to Act 3, and are recorded on H.M.V.C 2860-1. Although Toscanini has retiredfrom the New York Philharmonic Sym-phony Orchestra, he will still appear 'withthem occasionally.

Dancing TimeROY FOX and his Orchestra have

recorded " Poor Little Angeline "and " Calling me Home " on H.M. V.BD 5075, also " My First Love Song "(from the film,. Queen of Hearts) and" Would You " on H.M.V. BD 5076.

Joe Loss arid his Orchestra contributetwo lively dance numbers, " I like Bana-nas" and Madame-ah ! La Marquise-ah ! on H.M.V. BD 5080, also CubanPete," and " At the close of a long, longday " on H.M.V. BD 5079. These records

are interesting in view of the recentpublicity given to Joe Loss in_ connectionwith his dance tempo, which is consideredto be ideal.

"Fats" Waller new recordings are" All my Life," from the film " LaughingIrish Eyes," and " Cabin in the Sky "-H.M.V. BD 5077. These tunes should pleasethoie who like rhythmic piano choruses.

In the Swing Music series, four recordsare released this month; of these, one ofthe most representative is ," You StartedMe Dreaming," and " Torthented," playedby Wingy Mannone and his Orchestra,on H.M.V. B 8451.

Decca Records" A LEXANDER'S RAGTIME BAND''

and " Broken Doll," are two oldtunes that are served up anew

this month by. Brian Lawrence and theLansdowne House Sextet on Decca F 5981.

" These Foolish Things," coupled with".Lights Out," on Decca F 5987, is thelatest Greta Keller recording, and DannyMalone, the Irish tenor, sings " The Gloryof Love" and "Poor Little Angeline,on Decca F 5988.

Jessie Matthews has ,recorded four num-bers this month, from her latest film " It'sLove Again." They are : " TVs LoveAgain" and " Tony's in Town" on DeccaF 5982 ; and " I nearly let love go slippingthrough my fingers " and " Got to dancemy way to Heaven " on Decca F 5983.In the recorded version of " Tony's inTown" and " Got to dance my way toHeaven," you hear her tap-dancing aswell as singing.

Brunswick RecordsTHE third " Show Boat " film is

being presented in London, andbefore very long it will go therounds of all the big picture theatres.

Although it is a new film, so far as it wasmade quite recently,- two of the originalartistes appear-Paul Robeson and HelenMorgan. Those readers who would liketo hear these two artistes should obtainthe Brunswick " Show Boat " Album,which consists of four records, with anartistic album, which can be purchasedfor 16s.

Bing Crosby makes a new recordingthis month on Brunswick 0 2223. Forthis record he has chosen " Would You "and " Robins and Roses."

THE WIRELESS CONSTRUCTOR'S

ENCYCLOPIEDIABy F. J. OAM M 4th(Editor of PracticalLI

Editionand Amateur Wireless" ) net.

Wireless ' Construction, Terms, andDefinitions explained and illustrated

in .concise, clear language.

Over 150,000 Copies Sold!

From all Booksellers, or by post 5/6 fromGeorge Newnes, Ltd., 8-11, Southampton

Street, Strand, London, W.C.2.

Or 2/6 down and 10 monthlyPayments of 3/-.Comprises all parts for build-ing, with wiring diagram,assembly, and operatinginstructions, less cabinet.

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Send us a list of parts or valves you require or any speakeror set you ?nay select and we will forward yore a definiteemotaticrn. Ten years' advertiser in the Wireless Press.

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516 PRACTICAL AND AMATEUR WIRELESS

Director of StaffTraining

THE B.B.C. an-nounces that Mr.

G. C. Beadle has been appointed Directorof Staff Training in the training reservewhich will be formed on October 1st next.The Chief Instructor will be Mr. E. A. F.Harding, who is at present NorthernProgramme Director.

The purpose of the training reserve is toprovide newly recruited staff with a trainingin broadcasting methods, to keep existingheadquarters and regional staff in touchwith the latest developments, and to createa small reserve of staff for emergency andholiday requirements.

Mr. Beadle, who is now Director ofProgramme Administration, will be suc-ceeded in this position by Mr. R. J. F.Howgill.

Mendelssohn ConcertoMAURICE COLE will play the 3ilendels-

sohn Pianoforte Concerto in D minoron July 29th (National), and ClarenceRaybould will conduct " Three JewishPoems " of Ernest Bloch, " The NoondayWitch," by Dvorak, and -" Variations onThree Blind Mice," by Joseph Holbrooke.

There will be a programme of light musicconducted by Joseph Lewis the same even--ing (Regional), and on July 30th (National)Barbirolli will conduct an Elegy andScherzo by Frederic d'Erlanger, and," Dances of Marosszek," by Kodaly. OnJuly 31st (Regional) Albert Coates -willconduct a first performance in England ofSymphony No. 2 of Dmitri Kabalevsky, aswell as a first performance of his ownPianoforte Concerto in C, which will beplayed by Frank Lafitte.

Television ProgrammesA LTHOUGH no definite programmes

have yet been prepared for television,the Productions Department has alreadysketched out a number of plans for the firsttransmissions from Alexandra Palace in theautumn.

Apart from the " family " entertainmentside, there is the question of " interest "features to be considered, these consistingof light programmes concerned with topicsof the hour, people in the news, and general

..subjects of the Magazine " type. Among1 he titles already suggested for these fea-tures are : " The Zoo To -day," " Car-toonists at Work,". Travel, "Learning toFly," " Radio Personalities " and " HouseFurnishing," " Games Indoor and Out-door," " Physical Training," and " WorldAffairs."

Broadcasts to Schools

FORthe seniors, aged eleven to fourteen,

there will be a new music course, aseries of concert lessons; " British History,",`.; History in the Making," and topicalevents. Other items are dramatic readingsfrom Shakespeare, book talks and experi-mental programmes of poetry and biographyin the senior English Literature course,broadeasts on biology bY famous biologists,a geography series on the New World bybroadcasters who have known and lived in

the countries they describe, and the modernlanguage broadcasts for French and Germanby E. H. Stephan and H. Winter.

A new series for. seniors. on Friday_ after-noOns will include feature programmes,broadcasts of actual events, topical talksand talks on films.

The Central Council for School Broad-casts now test under school conditions allsets submitted to them by manufacturersand publish a list of approved apparatus.

H.F. Mains InterferenceONE form of interference arises from the

presence of high-frequency currents inthe mains leads. An, H.F. choke will, ofcourse, prevent this trouble, but in view ofthe fact that the current passing is on thehigh side special chokes, must be employeddesigned to withstand the high currents.Such components may be obtained from thevarious firms whose advertisements appearfrom time to time in our 'ages, and it ispossible to_ obtain components rated up to300 amps, although, of course, such com-ponents are very expensive. For theordinary receiver, the cheaper type ofchoke rated at .6 amp and costing 3s. 6d.(Ward & Goldstone type) will be foundquite suitable.

Speedy RepairsIF a bias resistance breaks down in

either an A.C. or an A.C./D.C. receiverand a replacement is not available, a batterymay be used, connecting its positive socketto the valve and its negative socketto the H.T.-line in exactly the same posi-tion as the bias resistance is normally joined.Alternatively, the cathodemay be joined in the negativeline and the bias batteryconnected between the gridleak or transformer secondaryand the negative line in thesame manner as in a batteryset.A Seasonal Overhaul

WHEN overhauling yourset do not forget to ex-

amine flexible leads and theirconnections to see that nosingle strand is projecting andcausing a short, or is so -loosethat such a short may occurlater. See that wiring is wellaway from fixing screws orbolts, and in the case of faultswhich defeat your powers ofdetection ascertain that inno case have screws piercedthe insulation of wires orcoils. It is also a good planto test the insulation of com-ponents to their metal cases,especially when the casesare earthed. An instanceoccurred. recently of anL.F. transformer secondarybeing earthed to its case.Had this component beenmounted on a wooden basewith the case not earthed, thefault would not have beennoticed ; but the case beingearthed the result was thatthe secondary winding was,in effect, connected as ashunt to the grid -bias battery

August 1st, 193 6

which accordingly ran down --quickly andunder -biasing the valve followed withconsequent' -deterioration of quality,increased H.T. consumption, and damageto the. valve itself.

Warm WorkIN 1924, recording was carried out at theI " His Master's Voice " studios, at Hayes,Middlesex, the artist singing, or speakinginto a horn. As the studio was kept at thetemperature of soft wax, it was found verynecessary to. discard coats and vests androll up shirt -sleeves, before commencingoperations. :

Was recording more difficult in thosedays ? Yes,: because of the numeroustechnical diffictilties with which we had tocontend. Owing to space limitations, theprincipals had to sing the choruses inaddition to the solos, as there was only asmall horn in which to sing. Imagine whatit was like !-perhaps ten people crowdedtogether like flies round a honey -pot,bobbing down to sing choruses and jumpingup for the solos. In the circumstances, itwas a miracle that acoustic recording wasso successful.

Chemistry in RadioWHILST improved methods of making

Ferrocart allow it to be " worked "by stamping and piercing, And ,it possesseslower eddy current losses than compressedpowder cores, yet it has a comparatively lowspecific gravity, and hence a smaller per-meability factor, owing to the lower ironcontent for equivalent bulk.

THE RADIO EXHIBITIONAug. 26th to Sept. 5th.

Our Stand : No. 10 Ground Floor.Same Stand-Same Spot as Last Year

11..N?Ci' :;

4.4.,11;poLZy.

kiRtatiuiIII -:744, 7 we-Flo4/1Co 44 4, 4t,

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11.4:4 14 4141a1,447,17 iir

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'k..0.00, 9°4'141,1, do -low,-

T.,

1.41e314)P

An unused' testimonial, sent to the Marconiphone Company byMr; Chris Parker. The enoelope shown contained the covering

letter.


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0

1,1

SHORT WAVE I,

_SECTION

ULTRA -SHORT-WAVE radio is verymuch to the fore at the present

- moment, 'for in addition to its useTor various official services it has, as mostreaders know, been adopted as the vehiclefor the forthcoming television transmis-sions-wavelengths in the region of 7metres having been decided upon. Butwhat is of greater interest to the listener,as distinct from the television enthusiast,is the fact that the sound accompaniment-of the television programme is also to beradiated on an ultra -short wavelength,namely 7.23 metres.

This opens up boundless possibilities inmany directions ; new ideas and possibly anew technique in receiver design and inaerial arrays, both affording fresh interestsfor the amateur and the constructor as wellas to the professional engineer. One of themost important points about the -ultra-short wave sound transmissions, however,is the potentialities held out for vastlyimproved fidelity in tonal quality.

Four LinksHigh quality as applied to sound, broad-

casting depends upon at least four linksforming 1 chain of circumstances, each ofwhich must be favourable if high-classreproduction. of the programmes is -to beachieved. The first link is the actualtransmission, and the practical requirementis that the modulation of the carrier as it

_ leaves the transmitting aerial shall be afaithful replica of the actual programme.The second is summed up in the phrase" general reception conditions " and in-cludes such factors -as a consideration of themutual interference between stations, andthe absence or otherwise of various formsof electrical disturbance, either natural or_man made. Third comes the question of"set design, and last but by -no means theleast,- the ability of the loud -speaker to

reproduce faithfully the various musicalfreetuencies present in the output from theset.

Although certain of these points have fiespecific relationship to the 'ultra -shortwaves, each must be dealt with, for suchlimitations as may be imposedby them haveto be taken into consideration whenassessing the extent to which the ultra -short - wave sound transmissions - mayimprove the general standard of reproduc-tion.

- In the matter of transmission it may besaid at once that microphone and amplifierdesign have now reached a standard atwhich it is possible to transmit, ifdesirable,range of audio frequencies entirelyadequate to do full justice to any class ofaound-music, speech, or " effects." It is,;herefore, possible to include in the carrier

QUALITY REPRODUCTION ON THE ULTRA-SHORT WAVES

The Wider Use of Ultra -short Waves Provides Many Schemes forImproving the Quality of Reception - By H. J. BARTON CHAPPLE, B.Sc.

modulation frequencies covering practicallythe whole of the audible spectrum, and it isonly on account of the impossibility ofreceiving the higher audio frequencies underthe present condition of ether congestion inthe broadcasting wavebands that theactual frequencies transmitted are con-siderably curtailed.

There is only one other matter in con-nection with transmissions which need bementioned, namely, that, for technicalreasons which cannot be explained indetail in this article, it is found necessaryto adopt in the control room a process of" contrast compression" whereby theloudest sections of the programme arereduced somewhat and the softest sectionsamplified to a certain extent. The practicalresult is that the audible difference between

To ensure high quality on the ultra -shortwavelengths when using a superhet, a specialI.F. transformer of this type may be used.A band width of over 2 megacycles may be

obtained with this component.

fortissimo and pianissimo passages, thatis the light and shade of the music, is notso marked when reproduced by the speakeras it would be if the original performancewas heard in a concert hall. The necessityfor- this " mutilation " of the light andshade is, unfortunately, inevitable and willnot really be removed by transmission onthe ultra -short waves, but it may be notedin passingthat devices have been developedwhereby a. special circuit in the receiverrestores, to some extent, the contrast of theprogramme ; these devices being applicableto any type of receiver, and for any wave-

-band.

Reception ConditionsReception conditions at present reallyrepresent the main source of limitation of .the degree of tonal fidelity attainable. Of

the various aspects of reception conditionsthat of mutual interference between stationsis perhaps the most important. The causesof mutual interference have been describedmany times in these pagde and are generallyknown, but in view of the fact that trans-missions on the ultra -short waves will un-doubtedly effect a great improvement inthis direction it is advisable to deal withthe matter from a slightly different angle.To begin with, the fundamental conceptionof wavelength must, for the moment, beput aside and the carrier wave consideredas occupying a single fixed frequency in thebroadcast spectrum-a frequency of, forexample, one million cycles for a 300 -metrewave and so on. When the carrier ismodulated with sound the physical effectis to produce, on either side of the funda-mental frequency of the station, a band ofnew frequencies consisting of valuesbetween two limits-the upper limit beingthe fundamental station frequency plus thehighest musical frequency transmitted, andthe lower limit being the fundamental

station frequent minus thehighest musi frequencytransmitted. y reason ofthese " sidebands," as theyare called, each station mono-polises a band of radio fre-quencies equal in width totwice the highest musicalfrequency transmitted and,unless the fundamental stationfrequency of two programmesdiffer by at least this amount.their sidebands will overlapand interference will beexperienced.

Now assuming that thehighest audio frequency whichit is decided to transmit is10,000 cycles-a figure nonetoo high for even reasonablygood reproduction-it would

be necessary to select carrier frequenciesfor ., broadcasting stations at intervalsof 20 kilocycles per second in order toavoid all risk of interference. Themedium -wave broadcast band covers awidth of just 1,000 kilocycles, and on thebasis of a 20 -kilocycle station separationcontains room for only 50 channels. Butaccording to the latest list of Europeanbroadcasting stations, there are, in actualfact, nearly 110 channels allotted in thisband, corresponding to only 9 kilocycleseparation and, moreover, these channelsare shared by nearly 200 stations. Such adegree of congestion moans two things.In the first place, receivers must be madeso selective that they can separate stationsoperating on adjacent channels separatedby only 9 kilocycles. This is done by so

.. (Continued overleaf)

=:518 PRACTICAlli AND -.AMATEUR WliatilaSS .August lst,. 1936

-SHORT WAVE SECTION' (Continued from previous page)

sharpening the timing that all the side'hands are, cut off above 4,500 cycles oneither side of the station frequency sothat no note or overtone above 4,500cycles is reproduced. As quality repro-duction depends upon the due receptionand re-creation of these higher frequencies,

reproduction of the ordinary(broadcast progranimes is' impossible exceptin certain specially favourable circum-'stances to be explained later, or by manu-facturing an artificial treble response inthe set itself. The second' result of ethercongestion- is that, since very little above;4,500 cycles is able to be reproduced, there,tscmslittle point in transmitting frequen-cies greatly in excess of this figure, so thatthe programmes put out, from certain'stations are not so perfectly transmitted'as they might be.Relative Field Strengths,; There is another point in connection

with the question of mutual interference;between stations which ought to be ex-plained because it plays a big part inthe improvement which can be expectedwhen ultra -short-wave transmissions becomeavailable: It is that the degree of suchinterference depends to a great extentupon' the relative field strengths, at thepoint 'of reception, of two stations occu-pying_Adjacent or practically -adjacentchannels. If, by reason of a station'spower or the geographical situation ofthe listener's aerial these field strengthsare comparable, only the highest degreeof selectivity, equivalent to the veryserious cutting of the side -bands, willgive reasonable interference -free reception,of either, and even SO there is a considerablerisk Of some of the higher harmonicsof the unwanted programme obtrudingthemselves on the wanted programme'as " side -band splash "-that annoyingsemi -Whispering noise which sometimesmar; reception.P 7 It must now be shown how the selec-tivity difficulty is greatly eased, if notentirely removed on the ultra -short waves.'It has been stated that for reasonable'quality there is room for approximatelyfifty 'channels on the medium waveband,and this statement can be even qualifiediby saying that for really good quality

and the complete elimination of the risk'of interference, the frequency separationof stations 'should be further widened;reducing the 'number of available, chattnelsto, two: or three dozen only, a matterwhich is impOssible of achievement, havingin- mind the natural aspirations of themany different broadcasting stations. But'on the ultra -short waves, the frequencyrange correspOnding to the available bandof wavelengths is much greater. Forexample, between wavelengths of 8 and 5metres- the& is a frequency difference ofno less than 22,500 kilocycles per secondwhich, allowing for the very liberal fre-quency separation of 50 kilocycles betweenadjacent channels, gives room for 450stations. Probably, such a wide separationwould not be necessary, in which case thenumber of channels could be furtherincreased. Moreover, 5 metres and 8 metresdo not in any way represent the limits ofthe ultra -short waveband, and good resultshave been obtained on even 2 metres, sothat between 1,000 and 2,000 channelscan be accommodated.

Nor is this all, for the range of ultra-short-wave transmissions is more limited than forthe medium waves; which means that themore distant stations will not interferewith those closer to the listener's aerial,even if the station frequency separationwas not increased greatly beyond thepresent figures, so that still more stationscould be accommodated without fear ofmutual interference.

The ResultThe practical implications of these facts

are four -fold. In the first place frequencyseparation could be increased to valueswhich would make mutual interferencephysically impossible ; second, there would_,then be no reason for restricting the radia-tion of the widest possible band of audiofrequencies, thus greatly improving thequality of transmissions ; third, thelimited range of ultra -short-wave radiationsnot only assists in avoiding the risk ofmutual interference but offers possibilitiesof a wider choice of alternative programmesfrom local stations, either by - way ofseparate performances or through relaysfrom more distant stations. In this con-nection it is one of the disadvantages ofhigh -quality reception at the present timethat it must be limited to the reception of

trvery few programmes, for -in- verviewspots is it found possible to select morethap some half -dozen stations:7-and usuallyopt more than two or three, which ftrereceivable, under 'high quvlRy conditions.Fourth, the need for highly selective circuitsbeing eliminated; the Performance capabili-tias of receivers, from the quality point ofview,:cail be very greatly imProved, and thisbrings us to the third factor in qualityreception, namely the receiver.

There are two aspects of receiver designwhich mainly affect quality. The first isthe consideration of selectivity. The widerchannel separations permissible with ultra -short -wave transmissions, and the reductionof interference due to the more limiteddistances covered by the stations, willrender highly selective circuits for ultra -short -wave reception unnecessary so thatthe full advantage of the complete audioband can be taken. The remaining limitingfactor in the receiver is the fidelity of thefrequency response in the circuits, and inthis connection all that it is necessary tosay, is that it has been proved __conclusivelythat a substantially flat response curve isattainable readily over the whole of theuseful frequency range, and that nodifficulty of any kind need be anticipatedin the design and construction of high-fidelity sets.

The Loud -speakerFinally, but still of major importance, is

the question of the loud -speaker. It hasbeen shown that from the points of viewof transmission, reception conditions, andset design there is nothing to mar thechances of very high quality in ultra-short-wave programmes-but there remains theloud -speaker. Listeners must recognise thefact that it will be quite useless to attemptto obtain even noticeable improvement inquality, in spite of the wonderful possibilitiesof ultra -short-wave working, unless thespeaker used is capable of reproducing awide band of frequencies. A number ofsuitable instruments are available to -day,and even many of the less expensive" ordinary " speakers have frequency re-sponses beyond the capabilities of highlyselective receivers, and it is safe to say thatthe average standard of speaker respcgisewill be still further improved in order totake full advantage of ultra -short-wavepossibilities.

'Swedish RelaysISO far there has been no short-

wave relay of the Swedish pro-grammes, although roughly

twelve months ago we were told'that the Stockholm broadcastingauthorities were planning the'installation of a special trans-mitter for this purpose. You/may shortly hear excerpts of the[Stockholm-lVlotala radio entertainments on/about 25 metres, as I learn that a Swedish'amateur station, SM5SX, whose address islArtillerigatan, 77, Stockholm, proposes tocarry out such tests shortly. It is reportedthat the experiments are being made inconjunction with the Royal TechnicalInstitute of the Stockholm University.

New TransmissionsTwo new transmissions of which you

may care to make a note are KAZ, the40 -kilowatt transmitter of the R.C.A.(U.S.A.), which frequently relays Pro-grammes from the medium -waver " Radiot Manila " (KZRM, Manila, PhilippineIslands). The channel is 30.03 m. (9,990kc/s) and the time at which this broadcastwas heard was between B.S.T. 10.00-11.00.

,1=101 on 48.08 m. (6,240 kc/s). The

Leavesfrom a(phonetic : achay-oono -otchecoo),

I Short-wave Logg

call is Radio - difusora HI8Q

Emisora Reale. Althouh no

1

address is given, I understandthat reports should be sent toSenores Abbes y Garcia, TrujilloCity (Dominican Republic).

LINIMINHININI4/0041MHISIIIINAnother South American broad -taster which has been logged

more frequently during the past few days isYV7RMO, Maracaibo (Venezuela), whichwas working at the beginning of the yearon 51.46 m. (5,810 kc/s), and which is nowfound on 49.42 m. (6,070 kc/s) immediatelybelow the reading of OXY, Skamlebaek. Inits announcements it calls itself : La Rota -(ion del Pueblo y Papa del Pueblo, whichI translate as the People's Station and theFather ( ?) of the People. Here again thetransmitter does not seem to work to aregular schedule, but the broadcasts havebeen picked up between B.S.T. 02.00-04.00.Just below the condenser readings of JVN,Nazaki-Tokio (28.14 re.), you should tryfor CEC, La Granja, Santiago (Chile),which, operating on 28.12 m. (10,670 ke/s),with a power of 4 kilowatts is on the airnightly from 01.00-02.15.

W2XBG, Hicksville (N.Y.) on 46.67 m.(6,427 kc/s), is an experimental stationinstalled by Press Wireless Inc. for thetransmission of news bulletins " in clear."A search should be made for these signalsbetween B.S.T. 02.00-04.00.

We may shortly expect to pick up testscarried out by VK6ME, Perth (W. Australia)on 30.15 m. (9,950 kc/s), although I under-stand. that later it will use the same fre-quency as VK2ME, Sydney. The latestnews states that it may be ready by August.

South AmericansHI8Q, Ciudad. Trujillo (Dominican Re-

public), which must still be considered anewcomer to the ether, does not yet appearto possess a regular schedule, but may beheard on some nights testing broadcasts

August- 1st,. 1936 PRACTICAL AND AMATEUR. WIRELESS 519

METER SNAGSThe Beginner can Easily be Misled by the Use of Unsuitable Measuring Instrumentsand Some of the Pitfalls are Explained in this Article

THE amateur who is beginning totake a, keener interest in his hobbyof radio- often realises that one ofIthe first steps to a better knowledge is thea acquisition of a meter or measuring; instrument. He thereupon goes to .thenearest radio shop and obtains one ofa the popular "dual range or double-; reading voltmeters" which may beI obtained for a sum as low as 101d. Armed

a with this he attacks his radio problems; by commencing to test his H.T.; L.T. and' I G.B. batteries; and if the particular metera is also provided with a milliamp. scale he; includes it in some convenient part of theI circuit and then perhaps proceeds toa wonder why the current is so low, or why-; he gets such good results from an H.T.I battery which reads only 50 or 60- voltsa instead of 100 or more as he expected.; The old hand will realise the difficulties

which the beginner will encounter if hea proceeds to rely upon this type of instru-; ment, but, unfortunately, the oft repeatedI advice to purchase a meter having aa resistance of 1,000 ohms per volt is met! with either derision or amazement, and itI still appears that readers endeavour torely,upon the cheap type of instrument to; enable them to put a receiver in workingorder.

1- What Resistance MeansThere are many different types of meterI upon the -market, but we will first explain

a why the cheap double -reading meter may.! prove misleading unless used, only forI particular purposes.- On some of thesemeters it will be found that one voltagerange (generally 0 to 12) is' marked inr$ black figures, whilst the high range,

, generally from ,0 to 120, is marked in red/ figures, and upon the- face of .the instru-meat will appear the letter It followed by

/figure,, on one side of the dial in blackand on the other in red. These figuresI indicate the resistance of the meter onboth ranges, and a typical cheap meter! will probably befound to have values ofI 200 ohms on the low -voltage range and2,000 ohms on .the high -voltage range,and to many amateurs these figures mayI appear to be unimportant.

Applying Ohm's LawI Hdwever, from the familiar Ohm's Law,a we know that current is relative to voltageI and resistance; and therefore if we have

a meter reading 120 volts with a resistanceI of 2,000 ohms we can see that the currentpassing through that resistance (the meter)I will be 120 divided by 2,000, or 60- milli-, amps. How many small battery receivershave an H.T. consumption approachingthat value? Yet this means that- if themeter is joined across the H.T. battery'sockets in order to test the voltage' of it,

a very few seconds you will be taking asmuch from the battery as your receiverwould take in many'hours of listening.Apart from this, however, you will not geta true idea of the state of the battery forthe following reason. Suppose that thebattery has been in use for some long timeand is therefore in rather a poor state.Your receiver may consume, say, 10 or 15mA, and the battery may be, in suchstate that it can just about maintain thisload for another week or so without thevoltage dropping unduly. It is presumed, of course,' that the reader is aware thatcurrent and voltage are related, and thatas the current drain rises the voltagesupplied will fall off, and vice versa. Well,then, when the meter is applied acrosssuch a battery, owing to the much highercurrent which is taken to drive the meterneedle across the dial, the voltage which isindicated will be much less than the actualvoltage of the battery. It may be arguedthat this will result in the user throwingaway a battery which in any case is nearlyexhausted, and is thus likely to give rise to' trouble, but the main point is that the.user is deprived of some hours of goodlistening due to the sudden load whichhas been imposed on the battery.

The Grid BatteryIn the case of the grid-bias battery itmust be remembered that no current is,normally taken, and, therefore, if thecheap meter is used at frequent intervals

an unnecessary drain is imposed and thelife proportionately shortened. In theactual receiver circuit even more mis-leading results will be obtained, as inmany cases the current taken by, themeter will be added to that already takenin that part of the circuit, and thuswill,give either a lower voltage reading than isrequired, or will fail to give a reading atall. The latter trouble will occur- if thevoltage to the, detector 'stage is measured,as in this stage the normal current is onlyof the order of 1 mA or so, and therefore

the addition of a further drain of 60 mAwill show its effect in the voltage droppedacross the resistance in the anode circuit,in addition to which the, detector valvemay have a resistance of such a low valuethat it will also modify the current takenand so add to the trouble.

drop of 10 Volts would occur. If, now,

Measuring Anode CurrentSuppose that the amateur wishes toknow the anode current taken by theoutput valve. This may be about 9 or10 mA for good power valve, and

normally included in the anode circuitwill be a loudspeaker transformerprimary having a D.C. resistance ofperhaps 1,000 Ohms, across which a

included in series (as it would be to read Ithe anode current), a further drop of 20volts would occur, and this will, naturally !result in a Wrong reading being shown.

VersatilityFinally, the type of meter just referred

to will only be suitable for instantaneousreadings of voltage as delivered by theL.T. and H.T. batteries, and must there'-'fore be placed in circuit and removed as !quickly as possible, and beyond this theyhave no further application. On the otherhand, if the amateur obtains one of the ;better -class of meters having a resistanceIof 1,000 ohms per volt, this may be used ato test the batteries or to take actual !readings whilst the, receiver is working, Iand will give a true indication of the state aof affairs. A better scheme, of course, is to !obtain only a very low-reading-rnikiam- Imeter and to use this 4eonjunction withvarious resistances in order to take read-ings of voltage, current ar.d other things, Iand this will give the amateur not onlymuch better service, but m, ill provide him !with a device which will give many hours Iof interesting study in the way of showing'how various components function, the ;effect of different methods of coupling,and so on. Practically all the large -service-testing devices have as their basis !a meter such as this, and the money Irequired for such an item is well repaid, a

H.T. SUPPLIES I-!

IT may be noted that a transformer is Iconnected between the mains leads Iand the rectifier ; this serves the purpose aof isolating the mains from the receiver !and also drops or increases the voltage I 'to that required by the rectifier. The achoice of rectifier and transformer is

important, and therefore the beginner is $advised not'to' attempt the home -Con-struCtion of an A.C. unit without consult- !ing an experienced designer, or following Ia reliable published design.

The running cost of a mains unit isdecidedly lower than that of batteries, 1and therefore if a mains supply is avail- aable it is advisable to use an eliminator.A possible draw -back of the eliminator ascompared with the battery is the existenceof mains hum, but if the unit is well ;designed this should not, be sufficiently 1trong to affect reception materially.

1

a current of 60 mA will be drawn, and so in a further resistance of 2,000 ohms is A reliable A.C.-D.C. meter for all 1-ihrls of tests.Li/H111/1.1147..'

V..i)..M.041M1NEN' 1.411111.{PO;141111.1,11=i1.1//0.0.1111.....M.041.11.0.11.04(111=NNIMIN,41111'....114111004111 FeffM.1,i1

520 PRACTICAL AND AMATEUR WIRELESSAugust 1st, 1936

COMPONENTS TESTED IN OUR NEW LABORATORY

Midget AccumulatorsD EADERS who are building miniature1 receivers and similar apparatus util-ising the Hivac Midget valves and similarmidget components will be interested toknow that special midget accumulatorsare now available from the A.E.F. Manu-facturing Co., of 17, Queensway, PondersEnd, Middx. These accumulators aresupplied with the jelly electrolyte and arefully charged ready for use. They shouldbe given a re -charge when the voltagedrops to 1.8,-Arolts, or at least every threeor four weeks, whether the accumulatorhas been in use or not.

To re -charge it is only necessary toremove the stopper, add sulphuric acid11.200 Sp.G.) just sufficient to moisten thejelly and to charge at the rate specified onthe label for approximately twelve tosixteen hours. After charge, and beforeputting the accumulator into service, allexcess liquid should be drained off and thestopper replaced.

A range of 2 volt Midgets is given below,but the makers can supply any particularshape,rsize or capacity to special order.

t^

11

D..10<fi

o A

'eE

al

-''Apl

Overalllininx

E.PIsPam

g

4 In;

.4

0

r4

24

.,_sIA IXI

E-4a5

N. 1 2 .2 11 1 3 8 4/9

NI 2 2/ .25 If 1 33/is 9 5/-

113 2 .2 31 1 21 6 4/9

31 4 3 .3 21 1 21 10 5/6

M 5 4 .4 31 1 21 12 5/8

M 6 4 .4 31 13/16 21 12 5/9

M 7 5 .5 2i- n 31 15 6/3

M 8 7 .7 3/,,

2/ 21 17 9/9

C P 5 10 1 2 11 5 24 7/6

New H.M.V. Receivers'ALTHOUGH details of the H.M.V. new

range of instruments are not yetavailable, it is stated that it will be one ofthe most comprehensive planned by thecompany. Full details, with specifications,prices and descriptions, will be publishedon August 10th next, but it is announcedthat the models already released will besupplemented by a series of battery re-ceivers, mains receivers and radio -gramo-phones based on a family of 3 valve, 4valve, 5 valve and 6 valve all -wave chassis.

New Colvern CoilsTEN new types of " Colpak " tuning

unit have now been added to theColvern range, bringing up the total totwelve models, suitable for practicallyevery need, and ranging in price from£1 19s. to £3 15s. 6d. These tuning unitsconsist of a set of Ferrocart iron -core coilsand a ganged condenser, ready wired andready for inclusion in a receiver. Various -circuit arrangements are employed, includingthe superhet, and the full rangewill be shownat Olympia, together with a large number

of the existing components which will beretained for the coming season.

Osram Gas -filled RelayAN argon -filled relay, type GT1B, is

shortly to be released by the GeneralElectric Company. This is of particulafinterest in the construction of televisiontime -bases and similar apparatus, and isprovided with a heater rated at 4 volts1.3 amps., and is fitted with a standard5 -pin base. The price is 20s.

Radio -meter Test EquipmentANUMBER of new test instruments will

shortly be introduced by Radio-'meters Ltd. and will be seen at the forth=coming Olympia exhibition. An adaptorand Allvalve Tester will appeal to theserviceman, as they enable all valves to betested and include a 36 socket panel. Ahigh -resistance moving-iron A.C. voltmeterwith four ranges from 5 to 1,000 voltscosting 3 guineas will also prove of valueto set -testers and servicemen, whilst for resistance and capacity tests a special bridgewith a directly calibrated scale suitable formeasuring resistances from 100 ohms to2 megohms and capacities from .00002 to25 mfd. will be sold at 6 gns. A D.C. volt-milliamp-ohm meter with a resistance of1,000 ohms per volt is also to be listed at5 gns. and has ranges of 10, 25, 100, 250 and1,000 volts, 25, 100 and 250 mA and 1 to1,000 ohms.

Atlas Mains Units

MESSRS.H. CLARKE AND CO.

(Manchester) Ltd. announce twonew H.T. mains units both suitable for ClassB and Q.P.P. receivers, and delivering12 or 25 mA at 120 or 150 volts, accordingto the load. The first unit has three addi-tional H.T. tappings and costs £2 7s. 6d.,whilst the second has a similar arrangementbut incorporates in addition an L.T.trickle charger designed to deliver .5 amps.,for 2 -volt batteries. This unit costs£2 17s. 6d.

A Tropical S.W. SetMESSRS. STRATTON AND CO.,

makers of the well-known Eddystoneshort-wave apparatus, announce that theywill shortly be introducing a special batterysuperhet: designed primarily for use inthe tropics. Full details are not yet avail-able, but it is stated that the receiver willcover all the more popular wavebands andwill be known as the Eddystone All -worldEight.

Rothermel Tuning UnitA NEW tuning unit is to be produced

by Messrs. Rothermel Ltd., and isto be given the novel name of the " RadioHeart." This will consist of a tuning coiland condenser assembly, with the necessaryswitch and coupling components, valve -holders, etc., ready wired and assembled forinclusion in a receiver. It will cover theshort wavelengths from 16.5 metres upwardsas well as the normal medium and longwaves, and forms the nucleus of a superhetreceiver, complete -with oscillator section.The price will be £5 17s. 6d. ready alignedand calibrated, with an aeroplane dial.

',111.11.1111, 1.1MON tan. i .i,., .u.N.14i NmieI ha.0.041110.4=1.1.1.1.111041

REPLIES IN BRIEF 1

The following replies to queries are given in iabbreviated form either because ofnon-compliance i

jwith our rules, or because the pointraised is not ofgeneral interest.

0.1M.0.1111.0.111011.11111.10111.04111HHOIN NIM.I NM. NIPEN NEINMNJ

W. F. (Blackpool). The trouble may be due to theH.F. choke you are using or to the damping of theaerial and earth system. Have you tried a condenserin the aerial lead ?

I.. D. (Carlow). We cannot supply the blueprintand do not know where one could be obtained. Thereis no standard book on the subject for the amateurso far as we are aware.

F. C. W. (Henley-on-Thames). It is possible to doas you say, but results are not worth while. A lower -rated valve will give better results with the low H.T.-voltage.

F. S. (Edmonton). We have described severaleliminators of the type mentioned, hut you do notstate the current you wish to take. If you let us haveflirther details we may be able to recommend a suitablecircuit.

F. E. S. (Qaywood). We cannot supply a diagrainto enable- you to use up the old coils and components.If you wish to build the latest superhet we suggestthat you dispose of the present set as it stands andbuy the necessary new parts for the Superhet 4.

Q. T. Q. (Walworth). We do not advise you toattempt to bring the set up-to-date, but to find outwhat has gone wrong. It is obvious that some com-ponent has broken down and we suggest that youcheck the eliminator first, and then the L.F. couplingcomponents. Is the speaker in good order ?

K. J. R. (Edgbaston). As no current is indicatedwhen the set " goes dead " itwould appear that eitherthe L.T. or the H.T. is interrupted. The switch wouldbe the most likely cause of this and we suggest thatyou short-circuit the switch contacts with some barewire in ordeelo test whether or not this is faulty.

F. R. (Bookham). Try the H.F. choke. You willno doubt find that this is inefficient and may be dis-pended with in this particular circuit.

H. V. B. (Norwich). The choke should not be includedin the mains lead as it will not carry the current. Specialchokes are obtainable designed for this purpose.

J. E. (Holloway). Write to the WestinghouseCompany giving them full details.

B. A. (York). We cannot trace the firm and it wouldappear that they have gone out of business since thelast exhibition.

N. I. S. (Conway). We cannot service the receiveras it is not one of our designs. A good local radiodealer should be able to solve the mystery in a veryshort time with suitable instruments.

A. E. (Perth). We cannot trace the manufacturersbut suggest that you communicate with the A. E. F.Manufacturing Company, advertisement appearsin this issue. g ornpan-.v'

S. W. E. (Truro). We do not intend to issue anyinstructions until the transmissions commence. This

will avoid disappointment due to insufficient workingdata.

G. T. (Bristol). Neither of the valves should be used.You should communicate with the makers of the re-ceiver and obtain their advice as to the best type ofreplacement. "

F. R. (Blackheath). The dial is not novel and we haveseen several similar arrangements in commercialreceivers. However, perhaps you would prefer to getinto touch with some good patent agent with a viewto obtaining a more " official " view.

- M. A. F. (Coventry). If selectivity is your mainconsideration we suggest you consider a good superhet.A good dea!er may be able to give you a demonstrationwhich will enable you to judge the. particular localconditions.

G. H. (Dundee). Types 80 and 81 are not inter-changeable, as type 80 is a full -wave rectifier, whilst81 is a half -wave rectifier. Type 59 is a power am-plifier. Furthermore, type 50 and type -81 has a7.5 volt heater, whilst type 80 has a 50 -volt heater.Thus the valves are not suitable for replacement onewith the other.

A. T. (Newton Ramsbury). Unfortunately youraddress was torn from your letter and we cannot there-fore reply by post. We do not supply blueprints forcommercial receivers, and suggest that you coin-municate direct with the General Electric Company,Magnet House, Eingsway, W.C.2.

A. H. (Worth). We cannot trace the set referredto, and cannot insert requests for readers to supplyback numbers.

W. Y. (Birmingham). The trouble is probably inthe transformer primary winding and this may bechecked by short-circuiting the winding, when thenoise should cease. However, communicate directwith the makers or their local service agent.

L. P. B. (Bovington Camp). The fuse connection isquite correct. The S.W. Adaptor -converter, blueprintP. W. 48A, should be quite suitable.

J. B. (Hawick). No blueprint is now available forthe particular receiver mentioned by you.

R. S. O'B. (Dublin). We cannot recommend any of

our blueprints for the parts listed. You do not giveany coil types.

J. S. (E.9). A blue glow generally indicates that thevalve Is being over -run. This may be due to excessiveH.T. or insufficient G.B. and, therefore, these pointsshould be checked.

F. R. T. (Paignton). We have no blueprint of theparticular receiver nor of any similar set, but nextweek hope to publish details of a small portable whichmay meet your requirements.

."August 1st, -1936136!;,61CAL---AND'-AMATEUit -WIRELESS '521

UTTERS FROM READERSThe Editor does notnecessarily agree withopinions expressed by his

correspondents.iiiramie, Ur/AAA:44-\-714

afart

An Amateur's StationQIR,-As a regular reader of your very

interesting short-wave section, I trustthat the enclosed photo and details of myreceiving station will be of interest. Thesmall receiver to the left is a 1-y-1, the R.F.stage being untuned, and I use this entirelyfor reception of DX-CW with 'phones.Beside it is a 2-v-3, having two tuned R.F.stages, an R.F. pentode working as adetector, transformer -coupled to the A.F.stage, which in turn is transformer-coupledto two super -power valves in, parallel.This set is entirely home constructed, even' down to the metal chassis and tuningcondensers, and is the outcome of nearlya year's experiments. Stations from allover the world are received atlocal strength,Europe coming in with 'absolutely no re-action, and also America, given fair con-' ditions.

Trouble was at first experienced withselectivity, but I have cured this by makingmy own iron cored" short-wave coils.Loss of signals, due to the iron cores isnegligible, as the two R.F. pentodes pro-vide ample amplification.

-

The total anode consumption of this setis rather hefty, being 54 milliamps, so I amworking from wet H.T. cells. Regardingthe DX here, all continents have beenverified, and 57 countries, including suchplaces as Hong Kong, Bolivia, Peru, Salva-dor, Korea, Alaska, Mauritius, Hawaii,Ceylon, Siberia, Japan, New Zealand,Australia, and Ascension Island, etc.

The antenna has a 30ft. top, 30ft. downlead, is 30ft. high, and points due N. and S.

Sincerely hoping that the above will beof interest to your many short-wave " fans,"and wishing your excellent weekly everysuccess. -S. HOPPER (Brighton).

A Reader's CircuitQIR,-Re Mr. Parker's letter (July 4thN..) issue) and those of Messrs. Barce,Smith and Thornton (July 18th), I havebeen working. on such 'a set as they require,and havd evolved a circuit which- appears,to, be eminently suitable. It is a 5 -valvesuperhet on s. -wave bands, and a 3 -valve04-2 on medium and long waves. Thecircuit is extremely' simple, and suited toamateurs who have on hand spare com-ponents, as all componentsare quitestandard, normal det. S.G.and L.F. valves being used.The switching is also verysimple, i.e., one on/off switchand one 3 -position-, wave -change switch. This latterbring,s in on s. -wave anextra2 valves, making it a super -het. On M. and L. wavesthese 2 valves are cut out,giving L.T. economy.

The set, therefore, ischeap and 'easy to build, andif anything more ambitious..,is required extra stages couldeasily be added to my circuit,and. more modern valvescould Pe used. If anyorieinterested in details of thisreceiver I should be pleased

,to supply them;-CYRIL SALTER (Hayes).

All letters must be accoin-panied by the name andaddress of the sender (notnecessarily for publica-

tion).

A Good S.W. One-valverIR,-I built one of your short-wave

sets, a one-valver, last January, andhave been amazed at the results.

Here are some stations receivedZeesen on 7 wavelengths, 2R0 (25 and

31 m.), TPA2-3-4, HAS3, LRU, SPW,EAQ, LKJ1, PMN, OER2, RW59, CT1AA,,ORK, OXY, EIBP, VQ7LO, VK2ME,JVM, JVH, HVJ (19 and 50 m.), W3XAL,(16 and 49 m.), W2XAD, W2XAF, W2XE,W1XAL, W1XK, W3XAU, W8XK (19and 25 m.). On the amateur bands :-

G2-5-6-8, W1-2-3-4-5-6-8-9, F3-8, LA,EA1-2- 3-4-5-7-8, HB, PA, PI, CT, VE1-3, VO, ET, ON, OZ, SM, LY, OE, OK, I,

PY, YN, HI, U, NY, VU, VP6,YV,SU. I have also heard many amateur andcommercial morse stations. -N. L. PALMER(Thornton Heath).

CUT THIS OUT EACH WEEK.

-THAT when inductances are connected inparallel the total inductance is equal to thereciprocal of the sum of the reciprocals.-THAT instability when using a pick-up withlong leads may often be overcome by includingan H.F. choke in the lead from the grid with aby-pass condenser to earth.-THAT the tuned -anode circuit provides the

account is likely to provide most difficulty fromthe point of view of stability.-THAT when using an output filter circuitthe inductance of the choke will affect -theresponse and must be carefully chosen.-THAT ordinary flash -lamp bulbs are notsuitable for dial lights in a battery receiverunless a switch is included to open -circuit them fwhen a -station has been located.-THAT the reason for the above precaution iis that the current consumption of the average ibulb is equal to, and sometimes greater than,three ordinary battery valves.

The Editor will be pleased to consider articles of apractical nature suitable for publication in PRACTICALAND AMATEUR WIRELESS. - Such articles should bewritten on one side of the paper only, and should containthe nanze and address of the sender. Whilst the Editordoes not hold himself responsible for manuscripts, everyeffort -will be made to return them if a stamped andaddressed envelope is enclosed. All correspondenceintended for the Editor should be addressed.: The Editor,PRACTICAL AND AMATEUR WIRELESS, George Haynes,Ltd., 8-11, Southampton Street, Strand, W.C.2.Owing to the rapid progress in the design of wirelessapparatus and to our efforts to keep our readers in touchWith the latest developments, we give no warranty that

apparatus described in our columns is not the subject ofletters patent.

Mr. S. G. Hopper's station (see letter on this page).

14=1.0,=...0.1)41111.MN11M1111.M.111110111111MPO.M1.04,(1.11111Z

1 BOOK RECEIVEriPROBLEMS IN RADIO ENGINEERING, by E. T. A.Rapson, D.I.G. etc. ' 103 pp. (Second-Edition.) Published by Pitman, price 3s. 6d.

THIS book has been written to facilitate class -workin Radio Engineering and fully meets the require-ments of students who are preparing for the HigherNational Certincates in Electrical Engineering. Itincludes many problems and examples drawn frompast examination papers of the City and Guilds ofLondon Institute in Radio Communication, theInstitution of Electrical Engineers in Electrical Com-munications, and the University of London in Tele-graphy and Telephony. Forty-two separate subjectsate dealt with, varying from capacitance and induct-ance to television, and all the test questions whichare set in each section are referenced with regardto the examination paper from which they are taken.Ten' pages are devoted at the back of the book tosolutions to the examples given so that the studentcan his answers. The book will prove invaluableto the student for either class or private study.

RADIO CLUBSAND SOCIETIES

Club Reports should not exceed 200 words in length.and should he received Ptr,1 Post each Mondaymorning for publication in the 'Mowing week's issue.The West London Radio Society

AT the Annual Ealing Hospital fêteheld in Walpole 'Park on Saturday,July 4th, this society. provided a side-showwhich proved to be one of the most popular-and attractive of the tents in the park:There was an interesting display of oldwireless relics heside modern radio appara-tus, of acorn beside transmitting valves,of crystal sets beside radio-gramophones,and many loudspeakers, amplifiers andmicrophones.

A " radio car," constructed by one of ourmembers, which had to be steered over awinding' couirse without the neon lightstriking, which it did when the car wentoff the road, was of great interest to thecrowd. Gramophone records of one's ownvoice could be made in the same tent. Anenjoyable day was spent by all members ofthe society who helped at this function.

Particulars of this radio society may beobtained from the hon. sec., H. A. William-son, 22, Cambourne Avenue, West Ealing,W.13.

Irish Short-wave Radio ClubALONG -FELT want has been filled

by the inauguration of a short-waveclub for those keenly interested experi-menters who find that radio "still holds afascinating thrill if activities are directed onshort waves and their ultimate possibilities.The value of such an association to theexperimenter is incalculable in its scopefor the advancement of ideas through experi-mental work, lectures, testing and examina-tion :of new apparatus, and general poolingof ideas gained from research. At theoutset, work will be confined to receptiononly, but at a later .date the transmissionside will be dealt with, and it is planned toerect an experimental transmitter._formembers' . benefit. In addition theservices of two well-known Dublin amateurswill be available for lecture work. Theseare E.1.2.F. and E.1.8:13.

The terms of membership are :.Entrancefee 2s. ; weekly subscription, 6d. ; countrymembers, 5s. per annum. Meetings areheld every Tuesday evening at 8 p.m. inthe club's temporary premises, 47, DolphinsBarn St. Persons wishing to becomemembers should call at the club room on anyTuesday evening at 8 p.m., or apply byletter only to the secretary. communi-cations should be addressed to the Secretary,Club Room, 47, 'Dolphins Barn St.,Duicilin. Secretary : J. 0.' F. James, 3,Clare Lane.

522PRACTICAL AND AMATEUR WIRELESS

August 1st, 1936

Practical and Amateur Wireless

BLUEPRINT SERVICEPRACTICAL

STRAIGHT SETS.One -valve : Blueprints, 1s.

All -Wave Unipen (pentode)

WIRELESSBattery Operated.each.

Date of Issue. No. ofBlueprint

. . - PW31A

Two -valve : Blueprints, 1s. each.Four -range Super Meg Two (D,

Three -valve : Blueprints, 1s. each.Selectone Battery Three (D, 2 LF, (trans.))Sixty -Shilling Three (I), 2 LF

(R.C. & trans.)) . , . Leader Throe (SG, D, Pow.) ..Summit Three (HF Pen, D, Pen)All -Pentode Three (HE Pen, D

(pen.), Pen)Hall -Mark Three (SG, D, Pow.)Hall -Mark Cadet (0, LI' Pen

..(R.C.))

16.3.35

F. J. Camm's Silver Souvenir (HFPen, D (pen), Pen) (All-WaveThree) .. . .. 13.4.35

Genet Midget (D, 2 .LF (trans.)).. June '35Cameo Midget Three (D, 2 IF

(trans.) .8.6,35

1936 Sonotone Three-Four (HFPen, HIP Pen, Westector,Pen) .. - 17.8.35

Battery All -Wave Three (I), 2 LF(RMon.C. . ..

The)) 31.8.35itor

*(HF Pen, D, Pen) .. 8.2.36The Tutor. Three (HF. Pen, D, Pen) 21.3.36The Centaur Three (SG, I), P)

Four -valve : Blueprints, 1s. each. --

Fury Four (2 SG, D, Pen)Beta Universal Four (SG, D,

Cl, B)15.4.33

Nucleon Class B Four (SG, D(SG), LF,

SCl. B)

(, . 6.1.34

Fury FourSuper SG, SG*, D, Pen) -Battery Hall -Mark 4 (HF Pen, D,

Push -Pull) . -F. J. Camm's Superformer (SG,

SG, D, Pen.) .. ..

Mains Operated.Two -valve : Blueprints, 1s. each.A.C. Twin (D (pen), Pen)A.C.-D.C. Two (SG, Power) .. 7.10.33Selectone, A.C. Radiogram Two

(D, Pow.)

Three -valve.: Blueprints, 1s. each.Double -Diode -Triode Three (HF

Pen, D.D.T., Pen) .. 10.6.33

D.C. Ace (SG, D, Pen) .. .. 15.7.33

A.C. Three (SG, D, Pen)A.C. Leader (111' Pen, D, Power) 7.4.34

D.C. Premier (HF Pen, D, Pen) .. 31.3.34Ubique (111' Pen, D (pen), Pen) .

.

28.7.34Armada Mains Three (HF Pen, D,

Pen) .. - .. 18.8.34

F. J. Camm's A.C. All-Wave SilverSouvenir Three (HF Pen, D,Pen) .. 11.5.35

All -Wave " A.C. Three (D, 2 LF(B.C.)). - 17.8.35

A.C. 1936 Sonotone (HF Pen, HFPen, Westector, Pen) .. 31.8.35

Four -valve . Blueprints, 1s. each.A.C. Fury Four (SG, SG, D, Pen)A.C. Fury Four Super (SG, SG, D,

Pen) . . ..A.C. (11 Pen, D, Push -

Pull) . . .

Universal gall -Mark (HF Pen, 5,Push -Pull) _

SUPERHETS.Battery Sets : Blueprints, 1s. each.£5 Superhet (Three valve)F. J. Camm's 2 -valve Superhet

(two -valve) ..F. J. Camm's £4 Superhet

Mains Sets : Blueprints, Is. each.A.C. £5 Superhet (three-valve) ..D.C. £5 Superhet (three-valve)Universal £5 Superhet (three -

valve) ..F. J. Camm's A.C. £4 Superhet 4F. J. Camm's Universal £4 Super -

het 4 ..

11.8.34

2.12.33

18.8.34

22.9.34

9.2.35

13.7.35

1.12.34

11.1.36

SHORT-WAVE SETS.Two -valve : Blueprints, 1s. each.Midget Short -Wave Two (D, Pen) 15.9.34

Three -valve : Blueprints, 1s. each.Experimenter'S-Short-wave Three

(SG, D, Power)... The Prefect 3 (D, 2LF, RC and

trans.) .. 8.2.36

PW36B

PW10

PW34APW35PW37

PW39PW41

PW43

PW49P312

PW51

PW53

PW55PW61PW62PW64

PW11

PW17

PW34BPW34C

PW46

PW57

PW18PW31

PW19

PW23PW25PW29

PW35CPW35BPW36A

PW38

PW50

PW54

PW36

PW20

PW34D

PW45

PW47,

PW40

PW52PW58

PW43PW42

PW44PW59

PW60

PW38A

rwa9A

PW63

PORTABLES.Three -valve : Blueprints, Is. each.F. J. Camm's ELF Three -valve

Portable. (HF Pen, D, Pen).. 16.5.36 PW65

Four -valve : Blueprints, 1s. each.Featherweight Portable Four (SG,

D, LF, Cl. B) - PW12

MISCELLANEOUS.S.W. Converter -Adapter (1 valve) - PW48A

AMATEUR WIRELESS AND WIRELESS MAGAZINECRYSTAL SETS.

Blueprints, ed. each.Four -station Crystal Set.. AW427

1934 Crystal Set .. - AW444

150 -mile Crystal Set .. AW450

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, 1s. each.B.B.C. Special One-valverTwenty -station Loud - speaker

One-valver (Class B)

Two -valve : Blueprints, 1s. each.Melody Ranger Two (D, Trans)..Full -volume Two (SG, Det, Pen)Iron -core Two (D, Trans) ..Iron -core Two (D, QPP)B.B.C. National Two with Lucerne

Coll (0, Trans) ..Big -power Melody Two with

Lucerne Coil (SG, Trans) -.Lucerne Minor (D, Pen)..

AW387

AW449

AW388- AW392AW395

5.8.33 AW396

- AW377A

- AW338A- AW426

Three -valve : Blueprints, Is. each.Class -B Three (1), Trans, Class B) 2.4.33New Britain's Favourite Three

(D, Trans, Class B) .

D*15.7.33

Home -Built Coil Three (SG, ,

Trans) -Fan and Family Three (D, Trans,

Class B) 25.11.33£5 5s. S.G.3 (SG, II, Trans) .. 2.12.331934 Ether Searcher: Baseboard

Model (SG, D, Pen) 20.1.341934 Ether Searcher : Chassis

Model (SG, D, Pen) ..Lucerne Ranger (SG, D, Trans)Cossor Melody Maker with Lucerne

Coils _P.W.H. Mascot with Lucerne Coils

(D, 1W, Trans)..Milliard Master Three with

Lucerne Coils .. -£5 5s. Three : De Luxe Version

(SG, D, Trans) .. - 19.5.34Lucerne Straight Three (D, RC,

Trans) _ -All Britain Three (HF Pen, III, Pen)" Wireless League " Three (11F

Pen, D, Pen) .. . 3.11.34Transportable Three (SG, 1), Pen) -£6 6s. Radiogram (D, RC. Trans) -Simple tune Three (SG, D, Pen).. June '33Economy -pentode Three (SG, D,

Pen) .. .. Oct. '83

" W.M." 1934 Standard Three(SG, Pen) -

£3 3s. Three (SG, *D, Trans) . Mar. '34Iron -core Band-pass Three (SG, D.,

QP21) _ . June '341935 £6 6s. Battery Three (SG, D,

Pen) .. .. -Graduating to a Low -frequency

Stage (D, 2LF) -P.T.P. Three (Pen, D, Pen) .. June '35Certainty Three (SG, D, Pen) .. Sept. '35IHnitube Three (SG, D, Trans) .. Oct. '35

All -wave Winning Three (SG, II,Pen) ........Dec. '35

Four -valve : Blueprints, Is. 6d. each.65/- Four (SG, D, 1W, Trans) -" A.M." Ideal four (2SG, D, Pen) 10.9.33

2 H.F. Four (2SG, D, Pen) . -Crusaders' A.V.C. 4 (211F, D.,

QP21) .. 18.8.34(Pentode and Class -B Outputs for

above : blueprints 6d. each) .. 25.8.34Self-contained Four (SG, D, LF,

Class B) . Aug, '33Lucerne Straight Four (SG*, D, LF,

Trans) -£5 5s. Battery Four (11F, I21*,

2LF) .. Feb. '35

The H.R. Four .. .. Mar. '35

Five -valve : Blueprints, is. 6d. eachSuper -quality Five (2HF, D, RC,

Trans)May '33

New Class -B Five *(280, D, LF,Class B)

Nov. '33

Class -B Quadradyne (2811, D,Class B) . . Dec. '33

1935 Super Five (Battery Super -

het) . -

AW386

AW394

AW404

AW410AW412

AW417

AW419AW422

AW423

AWS37A

AW424

AW435

AW437AW448

AW451WM2.71WM318WM327

WM337

WM351W31354

WM302

WM371

WM378WM389WM393WM390

WM400

AW370AW402AW421

AW445

AW445A

WM331

WM350

WM381WM384

WM320

WM340

WM344

W11379

These blueprints are full size. Copies of appro-priate issues containing descriptions of these setscan in most cases be obtained as follows:-"Practical Wireless " at 4d., " Amateur Wire-less " at 4d., " Practical Mechanics" at 7)d., and" Wireless Magazine " at 1/3d., post paid. Indexletters " P.W." refer to " Practical Wireless"sets, " P.M." to " Practical Mechanics " sets," A.W." refer to " Amateur Wireless" sets, and" W.M." to " Wireless Magazine " sets. Send(preferably) a postal order (stamps over sixpenceunacceptable) to " Practical and Amateur Wire-less" Blueprint Dept., Geo. Newnes, Ltd., 8.11,

Southampton Street, Strand, W.C.2.

Mains Operated.Two -valve : Blueprints, ts. each.Consoelectric Two (D, Pen) A.C. 23.9.33 AW408

Economy A.C. Two (D, Trans) A.C. - WM286

Unicorn A.C./D.C. Two (D, Pen) Sept. '35 WM394

Three -valve : Blueprints, is. each.Home-loyer's New All -electric

Three (SG, I), Trans) A.C. - AW383S.G. Three (SG, D, Pen) A.C. A W390

A.C. Triodyne (SG, D, Pen) A.C. 19.8.- 33 AW399

A.C. Pentaquester (HF, Pen, D,Pen) A.G. . 23.6.34 AW439

Mantovani A.C. Three (HP, Pen,

£15 15s. 1936 A.C. Radiogram1111374

D, Pen), A.C. .

,(HF, D, Pen) .. Jan. '36 WM401

Four -valve : Blueprints, 1s. 6d. each.All Metal Four (2 SG, D, Pen) J uly '33 WM329

Harris Jubilee Radiogram .. May '35 W111380

SUPERHETS.Battery Sets : Blueprints, Is. 6d. each.Modern Super Senior .. - WM375

Varsity Four . , Oct. '35 WM395

Mains Sets : Blueprints, Is. 6d. each.1934 A.C. Century Super A.C. .. 10.3.34 AW425

lieptode Super Three A.C. May '34 Wb1359

" " Radiogram Super A.C... - WM366

1935 A.C. Stenode Apt. '35 WM385

PORTABLES.Four -valve : Blueprints, 1s. 8d. each.Midget Class -B Portable (SG, D,

LF, Class B) - 20.5.33 AW389

Holiday Portable (SG, D, LF,Class B)

7.

AW393

Trans). 212..9.3343 AW447Family Portable (HF, D, RC,

Two H.F. Portable (2 SG, D.,

QP21) . Ante '34 WM363

Tyers Portable (SO, D, 2 Trans) Aug. '34 W11367

SHORT-WAVERS-Battery operated.

One -valve : Blueprints, 1s. each.S.W. One -valve converter (price 6d.) - AW321),

S.W. One -valve for America ., - AW429

Roma Short -waver - AW452

Two -valve : Blueprints, 1s. each.Ultra -short Battery Two (SG det,

Pen) .. Feb. '36 WM402

Home-made Coil Two (D, Pen) - AW140

Three -valve : Blueprints, is. each.World -ranger Short-wave 3 (D,

Trans, Super-regen) .. 30.6.34 ANNV345358

RC, Trans) .. -AVExperimenter's 5 -metre Set (D,

Experimenter's Short -waver Jan. 19, '36 AW463

The Carrier Short -waver.. .. July '35 WM390

Four -valve : Blueprints, 1s. 6d. each.A.W. Short-wave World Beater

(HF Pen, D, RC, Trans) AW436

EmpireTrans)Short -waver (SG, .1),

Standard Four -valve Short -waver Mar. '35

Superhet : Blueprint, 11. 6d.Simplified Short-wave Super Noe '35 W11397

Mains Operated.Two -valve : Blueprints, 1s. each.Two -valve Mains Short -waver (),

" W.M." Band -spread Short -waver- A W453

Pen) A.C.

D, Pen) A.C./D.C. .. Aug. '34 1VM368

" W.M." Long -wave Converter .. WM380

Three -valve : Blueprint, 1s.Emigrator (SG, D, Pen) A.O.

:Four-valveBlueprint, is. 6d.Standard Four -valve A.C. Short -

waver (SG, D, RC, Trans) .. Aug. '86 W11.1391

MISCELLANEOUS.Enthusiast's Power Amplifier (1/6) June '35 WM387

Listener's 5 -watt A.C. Amplifier(1/6)

'35 WM392

Radio Unit (2v.)........Sept.orWM392 (1s.) Nov. '35 WM398

Harris Electrogram (battery am-plifier) . . Dec. '35 WM399

De -Luxe Concert A.C. Eleetro-gram .. . . Mar. '36 W3143

New style Short-wave *Adapter.(is.) .. June '35 WM388

Trickle Charger (6d.) .. .. Jan. 5, '35 AW462Short-wave Adapter .. . . Dec. 1, '34 AW456

Superhet Converter .. Dec. 1, '34 AW457

W31313W31383

August lst, 1936 PRACTICAL AND AMATEUR WIRELESS 523

Burnt -out Volume ControlI have built a three -valve A.C. receiver

in which the first stage employs a variable -mu R.F. pentode. This has never workedreally satisfactorily, and the control hasbeen jumpy. Twice I have replaced thecontrol, changing the value each time, butthe control works too suddenly and two ofthem have burnt completely out. Is itpossible to give any indication as to what iswrong? "-P. T. S. (Malichester).IF the wrong value of control has been1 chosen this will cause the erratic con-trol,. Normally the current flowing in thispart of the circuit should no cause a burnt -out, and we therefore suggest that you haveselected the wrong :type of circuit. In anA.C. H.F. stage the usual arrangement is toinclude the volume control as part of apotentiometer across the total H.T. supply,tapping off a portion for the application ofthe screen -grid voltage. It _would bepossible to obtain the latter voltage andyet leave a very high current across thepotentiometer which could cause a burn-out, but we would imagine that you 'haveselected the wrong values of resistance forthe potentiometer in view of the erraticvolume control. If components have beensupplied as' a kit;checkthe values of theresistances in the S.G. poIentiometer feed,and if colour coded make quite certain thatsome " noughts " haV'e not been missedout in calculating'the vabies._ If they arecorrectly colour coded `or marked, perhapsit would be as well to test them in case theyare wrongly marked, although this is hardlylikely.- 'L.P. Distortion

" My four -valve battery set has beengiving quite good results, but I have en-deavoured to improvequality and have metwith the following difficulty. The first L.P.stage was R.C. coupled, and the secondtransformer coupled,- using a ' trans-former. I wished to get better bass responseand changed the second stage to parallel -feed, but now I find that quality is worse,bass response is not so good, and thi-voltimealso is less. Is there any reason for thisthat you eafi see from the details I havegiven you? My aim Is better quality andmore bass."-G. R. T. (Norwieh).

THE transformer you were using is a veryhigh-grade component having a high=

inductance primary -winding, and' is fittedwith a by-pass Condenser internallymountedand joined across the primary. The highvalue of the inductance no doubt gave goodmatching with'your previous direct method

connection, and the new arrangementhas probably been adopted with a low -valuemode resistance in order to periniVampleEf.T. to be applied to the valfe7:, Come-juently the matching is not so' good androlume and quality, .have -.suffered. Theondenser across the primary must also beaken into account in these particular cir-umstances. We think you will find that byransferring the transformer to the firsttage, that is, so that the primary is in-luded in the anode circuit of the detectoralve, and by using the resistance -capacity

NQUIRIES*coupling in the second stage, thequality will be improved, but ampleH.T. must be employed to permit thesecond valve to have an adequateworking curve, or over -loading will

take place and destroy the advantagesotherwise gained.

Five- or, Seven -pin Pentodes" While looking through a valve book I

found that pentode valves could be boughtwith either five- or seven -pin bases. I under-stand that there are three grids, one plate, andtwo filament connections in a pentode. One,of the grids is connected to one side of thefilament and so this leaves five connections.What I cannot understand is why have aseven -pin base if only five pins are needed ?Are there more ' works ' in a seven -pinpentode ? R. (Longdon).

).0.414111111.411M0i1141110.0.111=4141HPM.111.14 /.1.11104111

I

I

I

RULESWe wish to draw the reader's attention to the 1fact that the Queries Service is intended- onlyfor the solution of problems or difficultiesarising from the construction of receiversdescribed in our gages, from articles appearing r.in our pages, or on general wireless matters. IWe regret that we cannot, for obvious reasons- -1

(1) Supply circuit diagrams of completemulti -valve receivers.

(2) Suggest alterations or modifications of $ii nporareceivers

described in our contem-.

(3) Suggest alterations or modifications tocommercial receivers. -

(4) Answer queries over the telephone.(0) Grant interviews to quensts.

Please note also, that queries must be limited -,to two per reader, and all sketches and -draw- Iings which are sent to us should bear thename and address of the sender.It a postal reply, is desired, a stamped addressed envelopemust be enclosed. Send your queries to the Editor,PRACTICAL AND AMATEUR WIRELESS, GeorgeNewnes, Ltd.. Southampton Street, Strand,

London, W.C.2.

WE presume that you refer to theindirectly -heated H.F. pentodes, inwhich a combination of electrodes as men-

tioned by you is to be found. In thefive -pin valve the control grid and thescreening grid are joined to two pins whilstthe heaters are also joined to two pins.The suppressor grid is then internally con-nected to the cathode which is joined to thecentre or fifth pin, the anode going to thecap on top of the valve. In a seven -pinvalve, however, the suppressor grid isbrought out to a separate pin so that it maybe joined direct to earth, as it will berealised that the cathode will be earthedthrough a' biasing resistor and it may befound, under some circumstances, that thestability will be improved when the sup-pressor is earthed direct and not throughthe bias circuit. To ensure stabilitythe seven -pin valve, when of the metallisedtype, also has the metallising brought outto a separate pin for a similar reason, andwe think you will find that the five -pinpentode is now only supplied unmetallised,whereas formerly the metallising wasconnected direct to the cathode.

Experimental Coils" As I wish to carry out some experi-

ments on the short waves I should be gladto know what you consider the best methodof arranging the tuning circuits. I am notyet certain what wavelength will be best formy experiments, and the new detectorexperiments I am going to carry out mayintroduce varying degrees of damping, ete.

Would you let me know what you thinkWould be the best method of building thetuned circuits to cover wavelengths fromabout 5 to 20 metres."-B. L. (Leicester).

AS there is some doubt about theperforinance of the receiver we think

it would be inadvisabl to endeavour to useseparate coils for aerial "'coupling,". gridtuning and reaction. We do not know,' Ofcourse, whether "your piOpoSedmental circuits will incorporate' a re -actionarrangement, but in any case by buildinga single self-suppOrting solenoid with heavygauge wire mounted on a 16w -loss bale, youcould fit clipi to the various leads and tap,these on to different parts of the coil in'order to obtain- the desired coupling ,andtuning range. Small clips may be madefrom springy brass and soldered to the -various leads. -Ballast Lamp

" I am trying out ,a universal receiverwith the D.C. mains type of valve. I haveseveral on hand and am_ Ant. Certain regard-ing the permissible variations in voltage,ete., which may be used in a single circuit.'Fuithermoh, for reasons of economy, Ishould like te use a standard electric lampfor voltage dropping and 'should be :glad toknow how t0ealeulate the correct type oflamp for any particular eireuit."-D, 0:(Henley).IT'will only be possible to use different

voltage - ratings ;when two or morevalves may be paralleled to obtain a similarrating to the`remaining ValVes. Thegoverning factor is not the voltage but thecurrent which is passed, and thus the valvesmust be- so arranged that the_total current'flowing thiOngli the heater circuit is correctfor each valve; and different types may be'used pr6vided that parallel and series cori.nections will enable this important point tobe 'obseiveV The pr-o1;4ni of selecting a!suitable electric lamp Was, dealt with in our,issue last week, and we refer You to that for,more detailed obseffitiOns.A Live Chassis

" I have a home -built mains set in whichI have used a chassis bought -PT, a surplusstore. This is painted with some" kind ofcream paint which. kyery hard, and I have,scraped this away for,parth eouneetionslThe set is unstable, however, and cannot bemade to work properly, and, in addition, if Iitouch the chassis I. get a tingling throughlmy finger as though it is alive.. Should this!be the case, or does, indicate some fauit14There isno actual shock; and even if I wet'my finger the effect does not rise above 'algentle tingling sensation which can be felt'as far as the first joint of the finger.". -71G. B. M. (Finehley).

),IF yOu"are on D.C. mains, there is a possi-,'bility that a mild shock will be felt.

when the chassis is touched, owing to thereturn path to earth through your body.'For this reason it is always essential tofit a fixed condenser in the earth lead toavoid blowing the mains fuse in the event'of the mains plug being inserted a certain'way round in the house socket. The'chassis was probably cadmium coated, andit is essential that this should be entirelyremoved for sound earthing. Without!further details, we cannot explain the reason'why the set is unstable, but as you areprobably on D.C. the above precautionsshould first be taken. With a set of this -type it is also advisable to try the effectof using the receiver without an earth con-nection.

The coupon on cover iii pallet be Iattached to every query.

401101/1111111.110.0.011.MINWINIMIMMANNWININENINI.401.0,111111N.il


Miscellaneous AdvertisementsAdvertisements are accepted for thesecolumns at the rate of 3d. per word. Wordsin black face and/or capitals are chargeddouble this rate (minimum charge 3/. Perparagraph). Display lines are charged at6/. per line. All advertisements must beprepaid. All communications should beaddressed to the Advertisement Manager,

Practical and Amateur Wireless,"8, Southampton Street, Strand, London.

RECEIVERS, COMPONENTS ANDACCESSORIES

Surplus, Clearance, or Secondhand, etc.

RADIOMART (G5NI)SHORT-WAVE SPECIALISTS

Everything a constructor requires. Lowest prices.No junk. Catalogue lid. shows thousands of bargains.During summer, few only shown below.

RADIOMART.Utility 2 -gang uniknob and dial,

3/11, 1,500 vt, Tubular condensers, 6d. ; Helsbyelectrolytics 8 rill. 500, 2/11, 4 x 4 mf., 1/6, 25 Inf.,25 v., 1/- etc.

RADIOMART.Smoothing chokes, 20 by 120 ma.,

3/11 ; 100 ma., 2/11 ; 40 ma., 1/11. Telsen Acetransformers, 1/11. Radiogrands, RG48, 2/9. BTHspeaker, 2/11.

RADIOMART. Varley iron -cored, 10/6. Bifocaldual-range coils. Very selective, 2/11; matched

pair, 5/3..D ADIOMART. Pushback wire 6 yds. 68., heavyIN 9d. ; 2 gross solder tags, 6d. Resincored solder,9ft., 6d. -

ID ADIOMART, Centralab pots, all sizes, 1/6;AN switched, 2/-. Tubular glass fuses, -2c1. -

RADIOMART. Igranic midget jacks, 3d. Milliam-meters, 25 ma. upwards, 5/9 ; super 6/9.

RADIOMART. Telsen H.F. chokes, 1/11 ; screened1/11. Utility 1936 SL wavelength dials, 3/11.

ADIOMART. Lissen 3Agang superhet kit coils,11 two I.F.'s ganged condenser, ditto Bandpass,ditto 2 -gang all wave, 10/- kit.

RADIOMART. Traders' monster bargain parcels,Value 14/10/0 for 10/- ; also 5/- parcels.

DADIOMART. Famous continental A.C. valves,11 4/6. American Durtron, etc. All types, 3/6.,Battery from 2/3.D ADIOMART. Utility 8/6, microdisc dials, 3/11.

Radiophone .00016 short-wave condensers, 3/6.Series gap twin,

ADIOMART. Ceramic all brass microvariables,IN 15 mmfd., 1/4. 40 mmfd., 1/7. 100 mmfd., 1/10.Short-wave HFC., 9d.

ADIOMART. Orders 5/- post free. Get our bar -IN 'gain catalogues. General lid. Short-wave, lid.44 Holloway Road, Birmingham. Tel.: MID 3254.

ALL goods previously advertised are standardlines still available. Post card for list free.

1 /AUXHALL 'UTILITIES, 163a, Strand, W.C.2.I V Over Denny's the Booksellers. Temple Bar9338.

'CONVERSION UNITSfor operating D.C. Receivers

from A.C. Mains, improved type, 120 wattsoutput, at £2/10/0. Send for our comprehensive list ofspeakers, Resistances and other components.

WARD,46, Farringdon Street, London, E.C.4.

Telephone : Holborn. 9703.

ALCO ELIMINATORS & CHARGERS. 4 H.T. taps.120V/150V. 20/30 m.a. 18/-, with charger 25/..

Charger alone 7/6. k amp. 11/-. Year's guarantee.Details free. P. & D. RADIO, 1, Goodinge Rd., N.7.

ANKRUPT Bargains. Blue Spot S.G. 3v., 65/-.B Alba B.G. 3v., 67/6. Lotus 4v. A.C., 77/6.G.E.C. Compact 3v., 42/-. Also Mullard 6v. A.C./D.C.,Truphonic, Ferguson and Pilot all -wave, etc. Largestock valves, components. A.C. P.A. outfit, speaker,microphone, £9. A.T.R. 200 -watt converter, 90/-.-Butlin, 6, Stanford Avenue, Brighton..

LOUDSPEAKER REPAIRSREPAIRS to Moving Coil Speakers, Cones and Coils

fitted or rewound. Fields altered. PricesQuoted including Eliminators, Loud -speakers Re-

ired, 4/-. L.F. and Speech Transformers, 4/- postFree. Trade invited. Guaranteed. Satisfaction.Prompt Service. Estimates Free. L.S. Repair Ser-vice, 5, Balham Grove, London, S.W.12. Battersea1321.

REPAIRS.-Transformers,Chokes, Speakers.

Motors, Rewinding. Quotations free.-Jackson,20, Donnington Road, Worcester Park, Surrey.

MISCELLANEOUS

SHORT WAVE on a. crystal set. Full buildinginstructions and crystal, 1/2 post paid.-Radiomail,Tanworth-in-Arden, Warwickshire.

MERICAN Valves. Guaranteed 6 months. 5/-.J-1 Proprietors, 9, Carthew Villas, Harnmersmith,W.6.

PREMIERSUPPLY STORESAll POST ORDERS should be addressed to-JUBILEE WORKS, 167, LOWER CLAPTON RD.,

LONDON, E.5.'Phone Amherst 2833 (Private Branch Exchange)Callers, as usual, to 20-22, HIGH ST., CLAPHAM,

S.W.4. (Macaulay 2381.)and 165 and 165a, Fleet St., E.C.4 (next to Andertons

Hotel). (Central 2833.)NOW READY ! Send 4d. in stamps for NEW.ILLUSTRATED GIANT CATALOGUE AND VALVE

LIST.

a SHORT WAVES. -CHORT-WAVE COILS 4 to. 6 -pin types. 13-26,S

22-47, 41-94, 78-170 metres, 1/9 'each withcircuit. Special set of 3 S.W. Coils, 14-150 metres,4/-, with circedt. Premier 3 -band S.W. Coil;11-25, 19-43, 38-86 metres. Simplifies S.W. re-ceiver construction, suitable any type circuit 2/-.

COIL FORMERS, in finest plastic materials,liin. low -loss ribbed 4-. or 6 -pin, 1/- each.

CONDENSERS,super ceramic S.L.F. .00016,

.0001, 2/9 each ; double-spaced .000015,.000025, .00005, 3/- each. All brass with integralslow-motion .00015 tuning, 3/9 ; .00015 reaction,2/9.

SHORT-WAVEKIT for 1 valve receiver or

adaptor, complete with chassis, 3 coils 14-150metres, condensers, circuit, and all parts, 12/6.VALVE GIVEN FREE.2 -VALVE 8.W. KIT, complete with valves, 19/6.

B AND -PASS KIT, 14/6 the lot. Lissen 3 -gangcoil unit. Utility 3 -gang condenser and

disc drive 4 valve -holders, chassis and blueprint.OUPERHET KIT, 15/6 the lot. Telsen Band-*, Pass Superhet Coils, I.F.'s, 3 -Gang Condenser,Disc Drive and chassis.SPEAKERS, K.B. 8" P.M.s 9/6, GoOdman 7"

P.M.s, 9/6, Rola 7" P.M.s, 10/-.

MAINSTRANSFORMERS. Premier wire -end

type with screened primaries.H.T.8 & 9 or H.T.10 with 4v. 4a C.T. and 4v. la.C.T., 8/6.250-250v. 60 m.a., 4v. la., 4 v. 2a. and 4v, 4a., allC.T. 8/6.350-350v. 120 m.a., 4v, la., 4v. 2a. and 4v. 4a.,all C.T., 10/6.500-500v. 150 m.a., 4v. 2-3a., 4v. 2-3a., 4v. 2-3a.,4v. 3-4a., all C.T., 19/6.Any of these transformers with engraved paneland N.P. terminals 1/6 extra.AUTO TRANSFORMERS, step up or down,

60 watts, 7/6, 100 watts, 10/-.MAINS VALVES, famous Europa 4v. A.C.

types, 4/6 each. H.L.; L., S.G., Var.-Mu-S.G., H.F.-Pens., Var.-Mu-B.F. Pens, 1, 3,and 4 -watt A.C. directly -heated output Pentodes.Full -wave rectifiers, 250 v. 60 m.a. A.C./D.C.types, 20 -volt .18 amp. S.G., Var.-Mu-S.G., H.,H.L., and Power.Following Types all 5/6 each. Full -wave rectifiers350v. 120 m.a. and 500 v. 120 m.a. 24 watt in-directly -heated Pentodes. Frequency Changers.Octodes and Heptodes.DATTERY VALVES. 2 -volts, H.F., L.F., 2/3.Id; Power, Super -Power, 2/9. S.G., Var.-Mu-S.G., 4 or 5 -pin Pentodes, H.F. Pens., V.-Mu-H.F.Pens., 5/-. Class B, 3/8.AMERICAN VALVES. Genuine American

DUOTRON, all types, 3/6 each. Hytronsuper quality, 3 months' guarantee, all types, 5/6.MI LLIAM METERS, moving -iron flush j' 24",

all ranges from 0.10, 5/9. Visual tuning,6 or 12 m.a., 5/-. Moving coil meters, 24" 0.1 ma.,18/8; 31" 0-1 m.a., 22/6. Multipliers, 1/- each.Westinghouse meter rectifiers, 17/6 each.DLEOTROLYTICS. U.S.A. 4, 8 or 12 mfd. 530 v.

peak, 1/9 each. Dubilier, 4 or 8 mfd. 600 v.3/-; 50 mfd. 50 v., 1/9 ;12 mfd. 20 v., 6d. ; 25 mfd.25 v., 1/-. T.C.C. 4 or 8 mfd. 660 v., 4/-; 15 mfd.50 or 100 v., 1/- 50 mfd. 12 v., 1/,Paper Condensers.' W.E., 250v. working 4 mfd., 2/-,2 mfd. 1 mfd. 6d..; 350 v. working 4 mfd. 2/6.2 mfd. 1/6, Dubilier 500 v. working 4 mfd. 4/-;800 v. 4 mfd. 6/-; 2 mfd. 760 v. 3/-.Wego 450 v. working 1 mfd.1/.., 2 mfd. 1/9, 4 mfd.3/- ; 700v. working 2 mfd. 2/-, 4 mfd. 3/6 ; 1,650 v.working 1 mfd. 3/6, 2 mfd. 5/6.TRANSFORMERS, latest type Telsen R.G.4

(list 1(list 12//6.6), 2/9. Lissen Hypernik Q.P.P.

2/(3), 3IKLIMINATOR KITS for A.C. mains. 120 v.E

20 m.a., 8/6 & 150 v. 25 m.a., 10/-, tappedB.G. det. and output. Complete Kit with long -lifevalve rectifier (replacement cost only 2/-).

FERGUSONALL -WAVE 6 -valve SuperheL

I 100/250 v. A.C./D.C. 17-2,000 metres (list26.15.0.

I ISSEN ALL -ELECTRIC A.C.4. S. Grid. Det.,6. Pen. and Rectifier, M.C. Speaker. (List£9.9.0.) Our price 65/-.p.E.c. AC/De ALL MAINS THREE. OurM price 75/-.Potentiometers by well-known makers. AR valuesup to 1 meg. 2/.. ; with switch 2/6.



SOUTHERN RADIO'S WIRELESS BARGAINS.ALL GOODS GUARANTEED AND SENT

POST PAID. -C PEAKERS.-Celestion Soundex Permanent Magnet,S 10/-; Telsen Permanent Magnet with ten -ratiotransformer, 12/6; Blue Spot 99P.M. ExtensionSpeaker, 20/-; 45P.M. Extension- Speaker, 17/6;Telsen Loud Speaker Unit, 2/6; all new and boxed.

RECEIVERS.-G.E.C, A.C. D.C. Mains Three -valvesets. Complete with 3 Osram Valves, in ex-

quisite Bakelite cabinet with Osram M.C. Speaker,Ready to plug in to any mains. Fully guaranteed.New, in sealed cartons, £3/5 (list £7/15).G.E.C. Colpact 3 -valve Battery Sets complete with3 Osram valves, moving coil P.M. Speaker in attraetiveBakelite cabinet, makers' 1936 series in original sealedcarton, 50/- (List £5/10/0).MULLARD M.B.3 three -valve battery sets. Completewith batteries, accumulator, M.C. .Speaker. ThreeMullard Pentode valves in beautiful walnut cabinet.Brand new, in sealed cartons, £4/10 (list 18/8)-

TELSEN A.C. D.C. MTJLTIMETERS (latest 1936type). -5 -range for every conceivable test for

radio and domestic electrical appliances, 8/6 each.COILS.-TELSEN (1936). Iron -cored Coils, Type

W349, midget size, 4/-; type W478 (twin), 9/-pair; type W477 (triple), l6/- type W476 (triplesuperhet selector and oscillator), iey- set. All GaugedCoils are Mounted on Base with switch. I.F.-Trans-former Coils W482, 5/-; Telsen Dual Range Coil withvariable series condenser W76, 4/-; Varley SquarePeak Coils BPS, 2/-. '

ELIMINATORS.-Regentone (1936) Type W5awith trickle charger, 37/6; .Type WIa (less

trickle chatger), 32/6.HOUSE TELEPHONES. A SPECIAL BARGAIN.

BRAND NEW ONE -HAND TELEPHONES.Complete on stand, with or without Automatic Dials.Cost £4 each to manufacture, 10/- each.

MICROPHONES.-Ace (P.O.) Microphones, com-plete with transformer, perfect with any type

of receiver, 4/6.TRU-OHM RESISTANCES. -1 Watt. Wire ends

1, colour coded and marked ; 36 assorted capacitieson card, 6/-.

AMERICAN VALVES.-A full range of valves forall American Sets at 7/- each. Brand new,

guaranteed.

BARGAINPARCELS.-Parcel of Assorted Com-

ponents; including resistances, condensers, wire,etc., etc. ; all new and useful, value, 20/-; 4/6 perparcel. -

SOUTHERN RADIO BRANCHES. -271/275, HighRoad, Willesden Green, N.W.10 ; 46, Lisle Street,

W.C.2. All mail orders to 323, Euston Rd., N.W.1.SOUTHERN RADIO, 323, Euston Rd., London,

N.W.1 (near Warren Street Tube). 'Phone:Museum 6324.

3j each. RADIOGRAPHIC, LTD., offer all/ popular types American valves. 90 -day guaran-

tee. Full range in stock. National Union and Triadat keenest prices. Write for Lists. All GoodsGuaranteed. Satisfaction or money refunded. Orders10/- or over Carriage Paid.-Radiographic, Ltd., 66,Osborne Street, Glasgow, C.1.

NEW RECEIVERS, COMPONENTS,< AND ACCESSORIES

VALVES. By well-known manufacturer. Com-plete range of Battery, A.C. Mains, Rectifiers.

Brand new stock with six months' guarantee. 2 voltDetector, 2/3, Power 2/9, _Screen Grid, Pentode, H.F.Pentode, 5/-. The following American type valves,fully guaranteed, at 5/6 each : No. 80, 42, 43, 57,58, 77, 78, 6C6, 6D6, 25Y5, 25Z5. Write for otherprices to : Dulci Electrical Co., Ltd., 7, Lizard Street,London, E.C.1.

HULBERT for Quality Surplus Speakers. AllMusic Lovers should write for List 'of amazing

bargains._ Prices from 8/6 brand new. Made by bestknown British maker.-Hulbert, 6, Conduit Street,W.1.

Special offer screen -grid detector pentodechassis. Mullard valves, searchlight tuning,

by well -known -proprietary manufacturer.BRAND new, few only.

ALL lines advertised last week still available.

RADIO CLEARANCE, 63, High Holborn,' W.C.1.Tel.: Holborn 4631..

37/6

CLARIONVALVES.-All brand new, battery types

2 -volt, H.2, H.L.2, L.P.2, 1/9 ; super powerP.2, 2/6 ; screens and L.F. pentodes, 3/9 ; A. C. mains,

. 4 -volt, 1 -amp general purpose, 3/3 ; power, 4/-;screens and L.:F., pentodes, 4/6 ; full 'wave rectifiers,3/6.; postage paid, cash with order, or C.O.D. over10/ -.-Clarion Valves, Dept. 2, 885, Tyburn Road,Erdington. Birmingham.

August 1st, 1936

: '115.445M7,04' '

PRACTICAL AND AMATEUR WIRELESS

6

CONTENTS

FullyIllustrated

THE ART AND CRAFT OF, PHOTOGRAPHY. Sharpness inthe Right Place-Common Sense about Filters-GoodResults with a Simple Camera-Indoor Picture-making-Miniature Matters-Better Portraits-Successful Sunsets-Choosing a Hand Camera-The A B C of Composition-Points from the " Pro "-Exposure Simply Explained-Skies, Natural and Other-Why I Prefer Plates-Experi-ment or Experience ?-Winter's Opportunities-Makingthe Most of Co!our.PROCESSING MATTERS. A Beginner's Guide to Enlarging-The Improvised Dark -Room, etc.MONEY -MAKING PHOTOGRAPHY. Making Prints forReproduction-Newspaper Photographic Competitions-Prints in a Hurry-Pictures for the Press.CINEMATOGRAPHY. How to Make Good Pan and TiltShots-Choosin; a Cine Projector-First Steps inTitle-writing-Making Scenics-Don't Try It !-Intro-duction to Film Trick Work-Review of Progress-Useful Facts, Figures and Formula:.

EDITED BY FRANK WITTYand G. P. KENDALL, B.Sc.319 post free from the publishers,

GEORGE NEWNES LIMITED,8-11 Southampton Street, Strand,

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:V: 'AYvii: :1)1`I 02\Y

AND PRACTICAL TELEVISION

Practical and Amateur Wireless, August 8th, 1936

ULTRA -SHORT-WAVE AERIALS SEEPAGE 533

a GEORGEN EWNESAdflicaticit

Vol. 8. No. 203.August 8th, 1933.

MIDGETPORTABL

_LE NEWN ES TELEVISION AND. SHORT-WAVE HANDBOOKFully

Illustrated

By F. J. CAM M (Editor, Practical and Amateur Wireless, Practical Television, etc.)EVERYTHING ABOUT-Drums, Mirror Screws, Scanning Discs and other Scanning Systems, Neon Lamps, the Cathode -RayOscillograph. How to build Short -Wave Receivers ; How to build Ultra -Short -Wave Receivers, straight and Superhet types.

NEWNES FROM ALL BOOKSELLERS LONDONor Of. post free from 8-11, Southampton Street, Strand, W.C.2:net E-=

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PRACTICAL AND AMATEUR WIRELESS August 8th, 1936

HERE are the Holiday Books to give you theseaside spirit f Whether you are lazing

in a deck -chair, lying on the grass on the top ofthe cliffs, or perched at the end of, the pier, haveone or more of these Happy Holiday Magazineswith you.

Lively stories, laughable joke pictures and

cartoons, and the brightest reading for the

brightest time 'of the year!

j, THE SCREEN PICTORIAL SUMMER

r", ANNUAL is for every film fan,

different entirely from the 4 otherHoliday Books shown. It is lavishlyillustrated with fascinating photos, and

contains stories of your favourite stars

and films of 1936,Ask your Newsagent for

Screen Pictorial Summer Annual 65.London Opinion Holiday Number . Ed.Tit -Bits Summer Extra . . 6dHappy Holiday Extra . . , ti-Newnes' Holiday Annual .

August 8th, 1936 PRACTICAL AND AMATEUR WIRELESS 525

EASY FAULT-FINDING

radii

Technical Staff:W. J. Delaney, H. J Barton Chapala, Wh.$ch.,

B.Sc., A.M.I.E.E., Frank Preston.

See page 527

VOL. VOL No. 203. August 8th, 193.. 11111111111111=11

ROUND the WORLD of WIRELESSAll -wave ReceiversIN America a regulation has been intro-

duced to . ensure that the term" all -wave " is only applied to a receiverwhich tunes from 555 metres down to atleast 16.65 metres. It is claimed out therethat it is an unfair trade practice to describeany receiver as " all -wave " unless itembraces this particular band of wave-lengths. What does " all -wave " actuallymean ? In this country we find receiverstuning down to 12 and some only goingdown as. far as 19 metres, but in allof them there is a gap from 100 or sometres up to 200 metres. They are not,therefore, strictly all -wave, and it wouldappear that the term " four -band " wouldbe much more descriptive of this typeof receiver. Will the introduction ofthe television wavelengths lead to theinclusion of still lower wavelengths ? If so,then another new -term will, no doubt, beintroduced.

A New Use For RadioIN America a research worker has been

busy with an elaborate type of radioreceiver designed to assist him in studyingthe intelligence of rats and mice. He builta peculiar maze, having various doors whichopened, and some which did not, and elec-trical equipment recorded the actual passageof the rodent through the winding corridors.It was found that after one journey throughthe maze the rodent did not again enterpassages which had no outlet, thus puttingtheir intelligence on quite a high plane.

New Stations For GreeceTHERE is only one transmitter at

present in Greece (so far as officialrecords show), but we now understand thatthree stations are shortly to be built atAthens, Corfu, and Salonika, the ideabeing that Greek nationals in foreigncountries should be supplied with news fromGreece direct. No wavelengths have beenmentioned, but as the transmissions areapparently to be of the long-distance type,no doubt the short waves will be utilised.

Overcoming FadingIN commercial circles the elimination of

fading has often been carried out byutilising the receiver on two or moreaerials situated some distance apart, theidea being that the fading was at different

strengths in different localities and thus acombination of all signals would give areadable signal without fading. FromAmerica a new development of this schemeis announced, where two aerials are usedand each is fed through a separate channelin the receiver. The circuits are so arrangedthat as the signal on one aerial fades thegain of the associated channel falls andvice versa. In this way, a better signal-to-noise ratio is obtained than in the case ofstraightforward reception of long-distancesignals.

RADIOC1-f-M141AUGUST 26th

TOSEPTEMBER 5th

OUR STAND No. 10GROUND FLOOR

Same Stand, Same Spot aslast year, where we shallbe glad to meet all our

readers. I

Radio On RailsAN improvement on the railway radio

which has been tried in this countryhas just been tried out in France. The NordRailway Company has installed a com-plete studio in a coach, with arrangementsfor talks, lectures and various musicalitems, and with special booths for the useof lecturers, artistes, and others who maybe travelling on the train. In additiona powerful receiver is fitted and arrange-ments can be made to relay the receivedprogrammes to various parts of the train.

Welsh B.B.C. Education OfficerWALES is to have its own education

officer, and the B.B.C. have justappointed Mr. D. V. Roberts to thisposition, the appointment dating as fromSeptember 1st next.

Interference Investigation

THEproblem of interference with radio

receivers by electrical apparatus hasengaged the attention of the postal authorities for a long time. It was officiallyannounced quite recently that there are234 full-time engineers engaged incarrying out investigations in thisparticular direction.

Wireless in IndiaTO ensure reliability in air travel in India

the Indian Government has issued amemorandum concerning wireless facilitiesfor air transport in that area. All -mainsaerodromes are supplied with medium -wave transmitters and receivers. Thewavelength at present used is 900 metres,but if any great increase in the number ofaircraft is experienced another channel willbe necessary, and a short wavelength willthen probably be used.

Radio Picture S 0 SAN interesting example of the great

utility of the wireless transmissionand reception of a picture is afforded by therecent case of the broken submarine cableoff the coast of South Africa. The cablerepair ship proceeded to the vicinity, buthad not the necessary chart to locate thebreak. To avoid delay, the chart, with allthe essential information, was wirelessedfrom London to Melbourne, and thence tothe cable ship, which was accordingly ableto proceed to the spot and effect the neces-sary repairs.

Wireless and Flying BoatsTHE new fleet of Imperial Airways

Empire flying -boats will be fitted witha new type of radio equipment, experimen-tal models of which are now being perfectedat the Experimental Aircraft Establish-ment of the Marconi Company. The exter-nal wind -driven generators are eliminated,and dynamos and generators coupled directto the engine (internally) are to be em-ployed. The direction -finding loop aerialis also capable of being lowered through atrap-door in order to reduce wind resistance.In addition the wireless operator is to havea complete separate compartment withevery form of modern equipment, im-mediately behind the control cabin of theCaptain and First Officer.

526 PRACTICAL AND AMATEUR WIRELESS August 8th, 1936

THE PICK of the PROGRAMMES"Daventry Calling the British

Empire "A N electrical recording of a programme

Py broadcast the previous day to Empirelisteners will ' be given from the Midlandtransmitter on August 12th. This isdescribed as " A Visit to the EmpireTransmitters in Company with L. W.Hayes." It will include an historical anddescriptive account of the scene. Empiretest transmissions began at Daventry at

MAKE THESE DATES

/WITH YOUR RADIO

I 0 0 11 0 0 II 0 1 0 i "

world champion, Dr. Euwe, and threeformer world champions, Capablanca,Alekhine, and Lasker-as well as tourna-ments for players of lower grades. TheCongress lasts till August 28th. On August10th an eye -witness account of the opening

.OPEN-AIR RADIO

This happy group, snapped in Oxfordshire, gives some idea of the joys of a good portable, in thiscase the latest McMichael

the end of 1932, controlled by Mr. Hayes,and since the transference of the Nationaland Midland transmitters to Droitwich,the Daventry station has been entirelydevoted to Empire transmissions. Thenumber of transmitters and, aerials hasbeen increased, and the area covered hasbeen extended. Mr. Hayes is Director ofOverseas and Engineering Information atBroadcasting House. He was formerly theB.B.C.'s foreign liaison officer, and is itsdelegate to the Union Internationale deRad iodi ffusion.

Berlin Olympic Games : August 1stto August 16th

-rHE special arrangements for the broad-]. casts from Berlin will be as follows :-

August 6th. Final of the 1,500 metresflat.

August 7th. Final of the 400 metres flat.August 8th. Final of the 3,000 metres

steeplechase.August 1 1 th. Swimming Final of the

men's 4 x 200 metres relay, and the ladies'200 metres breast stroke.

August 14th. Rowing. Final of thecoxswainless fours and final of the eights.

August 16th. The closing ceremony.During the broadcasting of commentaries

by experts on specific events, it is hoped togive eye -witness accounts of eventsof general or particular interest that havejust taken place, so as to tell a generalstory of the progress in the Olympic Games.Chess Masters at NottinghamNOTTINGHAM is holding a special

N Chess Congress in which there willbe a Masters Tournament-including the

of the Congress will be broadcast from theMidland transmitter, and it is probable thatsome of the masters will speak. There willalso be a critic's survey of the Congress atthe close. The British Chess Federation arethe official hosts ; and the NottinghamAssociation the local hosts. The scenewill be the University College.

The " Summer Revellers "THE " Summer Revellers," presented

by George Hay and Gordon Lane,will be broadcast in the West Regionalprogramme, from " The Pavilion," Burn-ham -on -Sea, on August 13th, when thecast will include Betty Millar (soprano),Mildred Beaumont (comedienne), RuthBrandon (soubrette), Reg Back (lightcomedian), Rupert Harvey (tenor), EdwardWellington (entertainer at the piano), andBert Holtman (comedian).

" Top o' th' Towe;"C TOP 0' TH' TOWER " is the title of

1 the big Blackpool Night's Enter-tainment which is being presented byVictor Smythe for the benefit of Empireas well as North Regional listeners onAugust 13th. The dialogue has beenspecially written by Frank A. Terry, andthe show will be comOred by D. W. King.An intricate organisation of microphoneswill enable listeners to hear excerpts fromshows in progress at the Tower, Palace ofVarieties, Opera House, Empress Ball-room, Central Pier, Tower Circus, TowerBallroom, South Pier, South Shore, andPleasure Beach. Reginald Dixon, LarryBrennan's Band, Bertini's Band, and

George Lockhart (the famous EquestrianDirector) are among those who will betaking part, and it is hoped that there willbe contributions by 'Gracie Fields andGeorge Formby.

From All Over the RegionATRIPLE dramatic bill will be broad-

cast in the North Regional pro-gramme on August 10th. Manchester,Leeds, and Newcastle will be represented.Leeds' contribution is a Yorkshire comedyby Kit Higson, entitled " The Devil WasSick." This will be produced by James R.Gregson and Arthur Spencer. From Man-chester comes " The Moon," a short playby Dora M. Broom, produced by DavidOrmerod. Finally, Newcastle is representedby " Abigail Tysacke," " The Glass Blower'sDaughter," or " The Miracle of St. Mary'sWell," an old legend of the Ouse Burn,by Norman Veitch, ptoduced. by JanBussell.

Songs by German CampersFOR the All -Regions Children's Hour

on August 15th, there will be folk -songs by a group of German boys-mem-bers of the Youth Movement-who arecamping near Bromsgrove, in Worcester-shire. The same programme, which alsoincludes a play, will be broadcast in theEmpire Service earlier in the day.

To the Seaside and BackNOT long ago three young people from

the South Yorkshire coalfields weretaken on a day's trip to the seaside resortof Bridlington, where they availed them-selves of the usual holiday facilities foramusement-facilities with which, however,they were quite unacquainted. The ladywho accompanied them took a note ofeverything that was said that day, both onthe train journeys and at the seaside ; andon August 9th Northern listeners willhear what is to all intents and purposes aliteral transcription of some of their con-versation. It should prove a surprisingprogramme.

PROBLEM No. 203.Jones complained to his technical friend that

his battery set was consuming too 4auchcurrent from the H.T. battery, and' wasadvised to fit an economy type pentode inplace of the existing power pentode valve.When the substitution was made, however, hewas disappointed to find that quality wasvery poor and volume much lower than withthe old valve in use. Why was this? Threebooks will be awarded for the first three correctsolutions opened. Address your letters to theEditor, PRACTICAL AND AMATEUR WIRELESS,George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2. Envelopesshould be marked Problem No. 203 in theleft-hand corner, and should be posted toreach this office not later than the first postMonday, August 10th, 1936.

Solution to Problem No. 202.If the pentagrld valve was oscillating; a definite

increase in H.T. current consumption should beregistered by short-circuiting the oscillator reactionwinding or by short-circuiting the grid leak of theoscillator section of the valve.

The following three readers successfully solvedProblem No. 201, and books are accordingly beingforwarded to them: J. Armstrong,. 77, Earl's CourtRoad, London, W.8; ('has. Wright, 176, SissonsRoad. Leeds, 10; F. Williams, 36, Adam Street.Cardiff.


Easy Fault-findingW ithout Instruments Some Simple Tests which you can

Apply when the Set Ceases to Oper-

THE value of a good milliammeter ormulti -purpose instrument has oftenbeen stressed in these pages, but it

is surprising to find how many of the simplertypes of fault can be traced without theuse of any kind of meter. And when ameter is available it is often better to makea number of preliminary tests without usingit-even the experienced service engineerdoes not take measurements until he has

Fig. 1.-The on/off switchcan be checked by short-circuiting the terminals.The method with threetypes of switch is shown

here.

formed some kind of idea regarding thefault which exists. Moreover, all of thepreliminary tests depend more upon com-mon sense and a general knowledge of howthe receiver operates than upon advancedtechnical knowledge. Even the beginnercan find out a considerable amount bymaking simple and logical tests ; if he isthen unable to correct the fault he canmore easily obtain the necessary informa-tion from a friend or from THE PRACTICALAND AMATEUR WIRELESS Free AdviceBureau.

When the Set is " Dead "In the first place, let it be assumed that

a battery set which had previously behavednormally suddenly refused to " work."This must be due to a broken circuit atsome point in the receiver : a valve fila-ment might have burned out ; a wire mighthave come adrift ; one of the aerial, earth,or speaker leads might have broken orslipped away from its terminal; or a com-ponent might have developed a suddenfault. It is obvious that a start must bemade by carefully examining the con-nections, preferably by gently prodding "each wire with a pencil while the set isswitched on. If that does not yield anyresult, the effect of switching the set onand off should be observed. There shouldbe a click in the speaker when this isdone ; if not, the battery connection shouldbe suspected, whilst the effect of removingand replacing the H.T. wander plugsshould be tried. The accumulator terminalsand connections should also receive atten-tion, and any dirt or corrosion should bescraped away. See that the speaker leadsare properly connected to the receiver andto the speaker, and try the effect of short-circuiting the terminals of the on/off switchwith a short piece of wire, as shown inFig. 1. If the latter causes signals to return,

it will be evident that the switch is faulty.and should be repaired by bending thespring contacts, or else replaced.

Start with the Last ValveShould none of these tests give any indi-

cation of where the fault lies, and if thereare no sounds from the speaker when theH.T. wander plugs are pushed into thebattery sockets, it will be fairly safe toassume that the trouble lies with the lastvalve or with the loud -speaker itself. Itis, of course, assumed that it is known thatthe H.T. and L.T. batteries are in fair con-dition-if they are not, it is unlikely thatthe- set would become " dead " suddenly.

In order to test the valve properly, metersare required, but a good indication can beobtained by replacing it with one of theother valves in the set. Should it be foundthat the speaker then makes even a slightclicking noise when switching the set onand off, the valve can be suspected. Prob-ably the local dealer will loan a new valvefor the output stage so that a final checkcan be made. Assuming that there is stillno response, the speaker will come undersuspicion, and can be tested by connectingone lead to the positive terminal of theaccumulator and touching the other leadagainst the negative terminal. If thespeaker is in order there will be a fairlyloud click both as the contact is made andbroken ; absence of sound suggests that

Fig. 2. - Manyuseful tests can, bemade by touchingthe grid terminal ofeach valve -holderin turn with amoistened finger

tip.

the speaker is defective. A further testmight be made, however, by replacing theaccumulator with a 9 -volt G.B. battery.

Systematic Grid TestsDespite the absence of signals, it will

often be found that a click is heard in thespeaker when the set is switched on, orwhen the positive H.T. wander plug is

Fig. 3.-Progressivetests can be made byshort-circuiting thegrid circuits of differ-ent valves. Methodsare shown for trans-former and R.C.

couplings.

ate, when Signal Strength is Poor,or when there are Crackling Noises

inserted. It will then be evident that thefault is somewhere in the set prior to theanode circuit of the last valve. Moisten thefinger-tip, and touch the grid terminalof the output valve (see Fig. 2). A noiseshould be heard in the speaker when thisis done, but if not the transformer or gridcondenser and leak connected to thegrid (according to whether transformer orR.C. coupling is used) is probably at fault.Repeat this test by touching the gridterminals of preceding valves one at a timeuntil a point is reached at which no soundwhatever can be heard in the speaker.As soon as this valve is reached it willbe known that the fault lies in the circuitof that valve; the valve or one of thecomponents connected to it must be de-fective. The grid -circuit components canbe eliminated from the test by removingthe wire joined to the grid terminal andrepeating the test. If it is found that asound can then be heard, the grid -circuitcomponents arc known to be the cause oftrouble.

The tests described should make itpossible to locate the faulty part of the set,so that assistance can be asked, or so thatthe suspected components can be testedseparately or replaced one at a time. Thenecessary tests do not come within thescope of this article, but they have beenfully described in previous articles in thisjournal.

Crackling NoisesInstead of the set being completely

" dead," we might now consider theprocedure when trouble is experienced dueto crackling noises. Actually, most of thetests described can be applied in the firstplace, but others are necessary. The firstshould be to disconnect the aerial and earthleads and see whether the trouble ceases;if it does, the cause must have been inter-ference from outside the set, when morethorough tests must be instituted. Butshould it be found that the disconnectionhas no marked effect, the set should againbe examined for bad or loose connections.See that the valves are fitting tightly intheir holders ; gently press each from sideto side to see if the valves arc loose, or ifthe holders are damaged. Tighten up theterminals on all components, and clean anythat appear dirty. Make sure that theH.T. wander plugs are clean and fittingtightly, and look for partial short-circuitsbetween any two wires, between a wire anda screen, or between the metallised coatingof a valve and a lead running close to it.

(Continued on page 538)

4:;


' I Non -Standard ValvesAlthough the Majority of Valves Are Now Standardised and Similar Types May beFound in Most Manufacturers' Lists, There Are One or Two Isolated Types WhichMake Interesting Circuits Available to the Experimenter. -

THE amateur who makes a point ofstudying the various catalogueswhich are issued by wireless com-

ponent manufacturers will find that in'certain cases specialised components aremanufactured by individual firms and'cannot be obtained from any other source.In the case of wireless valves, it will befound that the majority of types may beregarded as standard and each manufac-turer makes a similar type, in most casescarrying a reference number which is also

220 V

with this distinction, that the two triodeseach possessed the variable -mu charac-teristic which is usually associated onlywith an H.F. tetrode or pentode. The valvewas used in a circuit designed to restorethe balance of volume obtained both fromstandard broadcasts and gramophone re-cords, a feature known as " automaticvolume expansion." It is well known thatthe normal reproduction from either theB.B.C. studio or a gramophone recordbas to be so balanced that overloading

does not take placeon certain passages.For instance, when

INPUTIP/CH-OP OR 5E79

.05 MED

Pis2

/Pro

250,00012

W6

0Pr

/0,000.4

oq

/400032

very similar. Thus, a battery detectorvalve having certain characteristics willreceive the designation 210 DET in one list,210D in another, and D210 in yet another.A careful examination of these valve listswill reveal, however, certain types whichoccur only in the list of one manufacturer,and the reference number will give no clueto the use of the particular valve. Thus,in the Ilivac list will be found the Y220and the Z220, whilst a battery valve,type DB240, will also be seen. In theMazda range there is an ACHL/DDD,although perhaps in this case the amateurmight hazard a guess as to the type fromthe initial letters. In the Graham FarishRing valve list will be seen the AC/PT,which, although revealed by the referenceas an A.C. mains operated pentode, possessescharacteristics which are found only inthe Harries type of pentode.

There was also another valve includedin the Hivac list (available in both batteryand mains types) which has, unfortunately,been discontinued. This was the type220V (mains type AC/V), and was designedfor a peculiar form of volume control.

Automatic Volume ExpansionThis valve has no counterpart on the

English market, although in America asimilar valve has been developed, butsuperseded by a different type of valve,consisting practically of a " variable -mulow -frequency pentagrid." The Hivacvalve consisted essentially of two triodesin one glass bulb, and in this respectresembled a normal Class B valve, but

Ts.

sooureor STAGE

listening to the newsbulletin, a certainvolume level is ob-tained. If the B.B.C.

o broadcast all itemsat a relative level, itwould be found thatshould the listeneradjust his volume sothat the announcerwas reproduced atcomfortable roomstrength, a militaryband- item which fol-lowed would raise theroof. Similarly, on agramophone record,there is a reductionin certain directionsto produce a balancewhich renders the re-production of such acharacter that it maybe comfortably re-

produced at good volume without dis-tress, but it is not a faithful reproductionof the original item. To carry out such areproduction it would be necessary todecrease the volume when the signal orrecord decreased in volume and vice versa,and the degree of modification which hasto be effected would vary in a peculiarratio. A complicated output circuit maybe designed for the purpose, but a simplerscheme could be carried out by using theHivac valve in the circuit recommendedby the makers and shown in Fig. 1.

rcr--

&AS-CONTROL VALVE

Fig. 1.-This is thecircuit which wasrecommended by themakers of the Hivac

valve for A.V.E.

HFCHOHEO

- By W. J. DELANEY

An Output CircuitThe effect is actually just the opposite

to the usual type of automatic volumecontrol which is fitted to most modernreceivers, in which the amplification isincreased when a signal decreases or fades.The effect of this control of volume is torestore the balance of comparative soundfrom various instruments, but I have metmany amateurs who do not like it. Cer-tainly, it is a matter of personal taste andcan be seriously overdone, but the circuitoffers interesting ground for experimentalstudy.

The Hivac type Y220 or Z220 valve is anoutput pentode, and may be consideredhere in conjunction with the GrahamFarish AC/PT, which is of similar design.The first thing which strikes the possessorof one of these valves is the remarkablylarge anode which is fitted and the tremen-dous space which separates it from theremainder of the electrode assembly. It isin this spacing that the critical design ofthe valve lies, and it is due to a researchworker named Harries, after which thevalve has been named. It was found uponexperiment that there was a vast differencein the performance of a valve as the distancebetween the grid and the plate was in-creased, but at one particular separation agreater output and sensitivity, with a muchlowerlevelof distortion, was obtained, and itwas found possible to calculate this distanceexactly. Accordingly, when this type ofvalve is employed, the usual " tone control"filter which is fitted across a pentodeoutput circuit may be dispensed with anda more brilliant reproduction may beobtained with the advantages above -mentioned.

Three in OneIn the case of the Hivac DB240 it will be

found that the internal electrode assemblyconsists of no fewer than three separatevalve elements in one single envelope,although a single filament serves all sections.The assembly consists of a single triode and adouble triode, or, in other words, a Class Bvalve, and the triode characteristics are of

(Continued on page 538)CLASS

LF TRANSFORP7ER

OUTPUTTRANSFORMER

Fig. 2.-A remarkable circuit which may be built round the DB240 valve.



M.C. Speaker MicrophoneHERE is a method of eliminating the

" heavy " effect produced when amoving -coil loudspeaker is used as amicrophone :

A sheet of bakelite is cut to cover com-pletely the diaphragm of the loudspeaker.A hole is then cut at the centre, of whichthe diameter is equal to the diameter ofthe speech coil. A tube, made of metal orthick cardboard, is then inserted into thehole until it is fin. from the spider or faceof the speech coil, and it is then mountedfirmly in position. The microphone iscoupled to the receiver or amplifier by meansof the output transformer on the loud -

Mr. George's sug-gestion for a M.C.

microphone.

SPEECHCOIL.

DIAPHRAGM.

)13a

CLEARANCE.

4 -----SPIDER.

METALTUBE .,

EBONITE ORBAKELITE:.

OUTPUTTRANSFORMER.

speaker frame. Since the sound wavesimpinge upon the speech coil and areprevented from acting upon the diaphragm,the response is more natural and the" heavy ' quality usually associated withthis type of moving -coil microphone isabsent.-J. M. GEORGE (Caerleon).

An Insulated ScrewdriverTHE diagram shows how an insulated

screwdriver can be made up out ofmaterials found in the scrap box. Theparts that I used were an ebonite tube,and a brass rod that I had used in the lead-in tube through the window, and a couplingoff an old tuning dial. It will be seen that

' different sizes ofNUT. drivers may be

FILLED WITH used. First, fastenCOBBLERS WAX the coupling on

HREADED ROD the end of rod6,1" LONG

COUNTER -SUNFOR NUT

EBONITETUBE 64' LONG

An insulated screwdriverfrom scrap material. 72xuZ.NuV;

GRUBCREW BOLT

Ts

WIRE SOLDEREDTO SCREW BOLTEDTO CAN,

WIRE SOLDERED TO NUTAND BOLT CONTACTINGTIP OF BULB,

CHISELLED SLOTS.IN LEATHER STRAP,

This device enablesyou to see into darkcorners of the set.

ELASTIC BAND,

TO 4-5v BATT:

Low -impedance speakers of about 3 ohmscannot be worked on this syStem asthe resistance of. the H.F. chokes wouldtake all the power.-R. V. PARSONS(Gloucester).

PRACTICAL MECHANICS6d. EVERY MONTH.

71,11M.0011q1141.11,.=1.11411 /011.1/11111.0.110,1140046M.11

110".0.11.=1.1 /1001.0410.01,41101.0.111i1.11.111.1,!11.1i

THAT DODGE OF YOURS!Every Reader of " PRACTICAL AND -1

AMATEUR WIRELESS" must haveoriginated some little dodge which would

Iinterest other readers. Why not pass it onto us? We pay £1-10-0 for the best wrinklesubmitted, and for every other item publishedon this page we will pay half -a -guinea. Turnthat idea of yours to account by sending itin to us addressed to the Editor, " PRAC-TICAL AND AMATEUR WIRELESS,"George Newnes, Ltd., 8.11, SouthamptonStreet, Strand, W.C.2. Put your name andaddress on everyitem. Please note that everynotion sent in must be original. Markenvelopes " Radio Wrinkles." Do NOT -enclose Queries with your Wrinkle.

where a flat is first filed, and then tightenthe grub -screw.. Next run the soldering -iron round (for those who cannot solder,I would advise two grub -screws). Nextdrop the nut in the ebonite tube where it iscountersunk and screw the rod in it ;fill the top in with cobbler's wax and it iscompleted. It would be as well to file aflat on the drivers so that they will notslip.-H. SCHOLES (Rochdale).

An Addition To the Test GearTO facilitate the servicing of sets where

illumination is bad, and where under -chassis work necessitates a torch, with thedetriment of having to hold or prop itin a suitable position, I constructed theapparatus as illustrated, and can vouchfor its decided usefulness in the test gear.

The construction is very simple, as thedrawing shows, and excepting that thosewho wish to make up this job may nothave the " can," as shown (this havingbeen procured from an old well-knownbinocular all -wave H.F. choke),no other difficulty should beexperienced.

No doubt other modificationswill suggest themselves, and Ihope the model illustrated willprove of assistance.-W. R.HOBBS (Ilford).

The H.F. chokes should be of low resist-ance the speaker one can be an old 150 or250 plug-in coil, but the one at the set endshould be screened or kept well away fromthe set.

An input impedance of about 2,000 ohmsis best, as this is a happy medium betweencutting of high notes by the H.F. chokes

TOtx=SPEAK

Using an aerial as an extension lcudspeakerlead.

and condenser, and resistance losses in theH.F. chokes.

The impedance of the aerial couplingcoil in the set being, at audio frequencies,only a few ohms, the aerial feed condenseris in parallel with the output, and boththe H.F. choices are in series with theoutput.

HFC.CAN. THREADED FOR

Ailf,AD6/ITHAn Extension Speaker CANCircuitWISHING to use a .speaker

at some distance fromthe house, I hit upon the ideaof using the aerial as a trans-mission line as well as for itsnormal use.

The circuit is quite simple and thespeaker is fed from any part of theaerial or down lead, through an H.F.choke to earth, needing but one leadfrom the aerial and an earth spike.

At the set end, if transformeroutput coupling is used, one side ofthe output is earthed and the otherfed through an H.F. choke to the aerial,the aerial being connected to the aerialterminal on the set by a small micacondenser of about .0005 mfd. If chokecapacity output coupling is used, oneside of the output is already earthed, itonly remains to couple the other side tothe aerial through the H.F. choke.


S. Iay

I ITV

1111'

August 8th, 1936. Vol. 3. No. 14.

Television Announcers as Make -UpModels

THE new television announcers-JasmineBligh, Elizabeth Cowell and Leslie

Mitchell-are to lend their faces to a groupof make-up experts for experiments atAlexandra Palace in August, the ideabeing to discover just what combinationof paint and powder are best suited tothe television transmitter. In the courseof the tests, which may last several days,the hostess announcers and their malecolleague will have to submit to almostevery type of facial make-up ; and theirordeal will not be lessened by the factthat the two different television systemsunder test-Baird and E.M.I.-call fordifferent colour treatment to get the besteffects.

Television Staff Moved to AlexandraPalaceZERO Hour " in television really

occurred last week, when Mr.Gerald Cock, Director of Television, andMr. D. H. Munro, Productions Manager,took up their new quarters in AlexandraPalace. During this week, the remainderof the Productions staff will move to thetelevision station.

One of the first problems to be tackledwill be that of studio lighting, and StephenThomas, the well-known stage ,director,and now a television producer, will concen-trate on this task in co-operation with thetwo newly appointed stage electricians.The dispositions of the studio lights andtheir general grouping will materially affectthe quality of the televised picture.

ServiceQ ERVICE in so far as it is related to radio

is to -day becoming a very specialisedsubject demanding' a thorough andup-to-date knowledge of measurements,fault location and problems of interference.The advent of television, especially duringthe initial stages, is sure to open up oppor-tunities for service engineers with a trainingin television technique. The standard ofreception will be raised and each setinstallation must be examined from quitea different angle than would be the case foraural radio. These points were referred tovery forcibly during the recent presidentialaddress to the Institute of Wireless Tech-nology. As far as is known this is theonly professional body of engineers whichhas a special examination in the subject oftelevision in order to qualify for associatemembership, while medals are also awardedfor outstanding contributions to the fieldof television research. In any case it seemsvery desirable that television service asapplied to the actual receiving sets shouldbe undertaken only by fully qualifiedtechnicians, otherwise harm may be doneto what is sure to prove a very flourishingindustry.

A Private Television DemonstrationAFEW days ago the Radio Corporation of

America gave an ambitious de-monstration of television reception in NewYork to a large audience of radio manufac-

turers. Transmitter and receiver were sep-arated by about a mile and an ultra -short-wave radio signal link was used. Iconoscopesformed the scanners at the transmittingend, while cathode-ray tubes functioned aspicture reproducers at the receiving end.A very varied programme of entertainmentwas televised, including dancing, fashiondisplays, comedians and short film excerpts.No doubt this was to show the standard ofperformance reached with the R.C.A. equip-ment, but it was emphasised that noattempt is to be made this year to markettelevision receiving sets for the Americanpublic.

IN BERLIN

This dose -up shows the two dipole aerial arrays on thetop of the Berlin Radio Tower. One is used for soundand one for vision, and it will be noticed that the aerialsare so arranged that the radiation is horizontally polarised.

An American Viewpoint

ITis interesting to note the point's of viewexpressed by the American Radio Manu-

facturers Association recently as far astelevision is concerned, for they regard itsimply as a logical future extension ofradio. The association is endeavouring toformulate plans which will ensure a servicecapable of covering the needs of the wholenation as far as possible. Unlike thiscountry, which is saddled with a doublestandard of definition and picture framespeed, the Americans are keen to find asingle set of conditions so that any set iscapable, without complication, of receiving

`any transmission within range. The pic-ture itself must be comparable with -home -movie quality. This last named is claimedto require a picture dissection of at least00 lines, although' it is realised that themodulation frequency to give full measureto this is at least six megacycles. TheR.M.A. are asking for an experimentalterevision signal band of frequencies startingat 120 megacycles (2.5 metres). On thiscarrier no difficulty will be experienced inworking the full modulation band, butpeculiar effects may arise owing to thehigher -degree of absorption, while screening -is more marked. A rather remarkablestatement was made to the effect thattelevision must be withheld from the publicuntil it is full grown, as it could not feelits way through the early stages of com-mercial growth as was the case with auralradio. This conflicts very forcibly withthe attitude of Farnsworth, who, as pointedout previously in this journal, welconied theactive co-operation of both the amateurconstructor and the general public, beingof the opinion that this would expeditegrowth and enable a satisfactory servicestandard to be achieved quickly.

German EnterpriseTHE Germans are certainly sparing no

effort in an endeavour to ensure thesuccess of the Olympic Games now beingheld in Berlin. Apart from the athleticside of the games themselves, it is nowannounced that no fewer than twenty-fiveviewing centres are to be established inBerlin where those sections of the eventsthat are televised can be seen on receivingscreens by members of the public unableto secure seats in the arena. The picturereproducers are to be cathode-ray tubes,and the screen size and brilliance will besuch that audiences' of fifty people will beable to watch each set that is employed.The resultant Press publicity which thiseffort will bring about is sure to add con-siderably to German prestige as far astelevision is concerned. With this will becoupled the ambitious plans for large-scaledemonstrations at the Berlin Radio Exhibi-tion also opening in August, a strikingcontrast to the present proposals now madefor our own Radiolympia.

Direct or Indirect ?NY MIEN the details of commercial

VV television receivers become avail-able it will be very interesting tosee whether direct or indirect pictureviewing will be the most popular. Inthe case of small size cathode-ray tubeswhose length is not untoward, then it seemscertain that the picture will be watcheddirectly as it is built up on the fluorescentscreen. The tubes can be mounted hori-zontally without making the set too deepfor comfortable accommodation in theroom where viewing is to be undertaken.With large diameter tubes, however, theresultant length of the glass bulb and neckwhere the electrodes are incorporatedmakes it rather awkward to house thetube horizontally. The best solution in thiscase seems to be that of vertical mounting.The picture traced out on the horizontalscreen can then be seen by observing itas a reflection in a miner inclined at anangle of 45 degrees. Care must be taken ;toensure that the mirror is of good qualityand not tob thick, otherwise a measure ofoptical distortion will evidence itself butapart from this the scheme seems a verysound one and enables the remainder of thereceiver equipment to be mounted veryconveniently in 'a cabinet standing nohigher .than a normal radiogram.


n our avelen thLost ChordsI WAS interested to read the other

day that a band leader playeda 'cello at Llandudno-made

it sing, sob, throb, and then suddenlymade it buzz, rattle and screech.He must have found the long lostchord, and he retired to investigate.Found his instrument full of glass-broken glass-a legacy from a motor -coach accident on the way downfrom London. Bram Martin was theman-the one who says that he willhave nothing more to do with womencrooners. The incident reminds meof an accident which happened someyears ago at a motor -cycling Gym-khana. A motor -cyclist skidded intothe orchestra, whereupon a flautistin his excitement swallowed severalinches of his instrument, whilst theman with the big drum, beat it.

I Split an InfinitiveG. H., of Bristol, takes me to task.

for splitting an infinitive in arecent note. By nature I am

a purist and a pedant, and must

Lost chords.

apologise for my lapse. It is un-fortunate, however, for my critic thatin his letter he should be guilty ofusing a terminal preposition which, Ithink, is a worse crime. He thinksthat the original Ford car and theAustin Seven were made famous byjokes and that if I continue to ad-minister my calligraphic flagellationcrooners, too, may become famous. Heomits to notice the subtle distinction ;both the Austin and the Ford aregood cars and no joke can assail theirmerit. But crooners do not possessmerit. This correspondent suggests asan interval signal a crooner trying toreach top C at the bottom of the sea.That's where they all ought to be-atthe bottom of the sea.

2y Thermion

Eye Bathing BannedTHERE are still a few creatures

who think that by means oftelevision we shall be able to

spy into one another's homes at themost awkward moments. With manyof these people the wish is father tothe thought. Perhaps they think theycan tune into Thermion, or theprivate lives of their neighbours. Onedear lady with imagination and per-haps hope, remarked at last year'sradio show that she really did notwant the B.B.C. to broadcast her inher bath. I hope I am not shatteringthe hopes of thousands of my readerswhen I say -that this cannot possiblyhappen. My readers will not be ableto look in arid see me some time. Assome slight consolation to theirthwarted desires I am therefore pub-lishing a sketch of myself in liquida-tion. Those readers who are not myfans will, of course, not be such cadsas to look at the sketch.

AnonymityONE of the questions recently

before the B.B.C. concernedthe announcement or other-

wise of announcers' names. Theproblem is not an easy one to solvefor various reasons, but how muchmore difficult it would become whentelevision programmes start ! If theB.B.C. consider it advisable still toenshroud their announcers in anony-mity, how would they manage ? Fora face is as good as a name for iden-tification purposes. I can only sug-gest that the gentleman whoannounces should wear a black silkdomino and the ladies some attrac-tive form of yashmak, but then I amtoo frivolous -minded to give thematter the serious attention it deserves.I have seen the two ladies who willannounce the television programmes.I have had tea with them. I canassure you they are most charming,and have the essentials of youth andbeauty. I always feared that theB.B.C. might pick a couple of frumpsbecause they had written a thesis onthe declining tendency of moderntimes ; or selected a couple of angularfemales of the duenna type.

Ho Hum

IRECENTLY encountered a

1 minor problem which almosthad me completely stumped.

A friend of mine (yes, I still havefriends) recently removed to a newhouse, and discovered that his sethad developed a hum rather annoy-ingly louder than that previously,experienced. He wisely invited my,counsel, and I, of my mere goodness,and graciousness, condescended tohelp him. He explained that he hadconnected his earth wire to the mainwater pipe in the loft. I suggesteilthat the earth was probably thetrouble, and was he quite sure he wasusing the main water pipe. He saidyes, he had asked the local plumber,and was quite satisfied on that point." Try another earth," I said. " Al-right," he replied. He fixed up anoutdoor earth with satisfactory results.Short time later he reported that theloft earth was now working O.K. butthat the outside earth was giving riseto hum. Together we tried the twoearths, but both were at fault.Eventually we discovered that the

Myself in liquidation.

trouble lay with the power point inthe wall, the plug of which, being astandard two -pin plug, could beplaced in the socket either way.

Radio ShowALREADY the staff is busy pre-

paring for the special Showissues. Olympia is upon us.

It seems only a few weeks ago that Iindulged in my annual peregrinations,quaffing the nectar, and strolling frombar to bar. This year:a exhibitionpromises to be the most interesting inthe whole series of the radio shows,for it will be the first in which tele-vision apparatus will be present withpublic appeal. Previously televisionapparatus interested but a com-

532 PRACTICAL AND

paratively small number of amateurs,but as we are promised television pro-grammes some time this year, nextyear, the year after, or at some evenmore distant date, the public mustthis year become interested in it.When the programmes do start Iforesee a great boom in home con-struction. It seems that the completecommercial television receivers willcost at least /j o, and I estimate thatit will be possible to make one forabout £20. The staff of this journalhave had in operation for more thana year a successful Cathode-rayTube television receiver. I wonder ifthe design will be unloaded this year ?The Editor in his wisdom refuses toinvite his readers to spend moneyuntil some programmes are available.Note to intending visitors to theexhibition-please leave your auto-graph books ; don't wait for me tosign them.

The Village ShopIT is interesting to note that J.

Breese Davies, a country shop-keeper from Dinas Mawddwy,

will give the fourth talk in the seriesentitled " Hen Gymeriadau Gwle-dig " (Old Country Characters) onAugust loth, when his subject will be" Siop y Pentref " (The Village Shop).The speaker is something more thana mere shopkeeper, for he has wonnumerous prizes at Eisteddofdau foressay writing, and has contributedmany articles to periodicals and

Preserving anonymity.k

magazines. One of his brothers is aminister in Sangareddi, and anauthority on Telugu ; another ishead of the Copyright Department ofthe British Museum, and his sisteralso writes. J. Breese Davies wasunfortunately debarred from a phy-sically active career by an illnesswhich caused him to be laid up forfive years in a Thomas Splint.However, he has derived a great dealof profit and amusement from hisdaily work as a shopkeeper and inhis talk on August loth, he willdescribe some of his experiences,pointing out the changes which havecome over his customers in lateryears, and showing how he and they

AMATEUR WIRELESS

Phone ReceptionIF reception is to be effected by

means of headphones, a three -valve receiver using an untunedH.F. stage followed by a triodedetector, resistance coupled to a smallpower valve, can "generally be reliedupon to give a very satisfactoryperformance. If a speaker is to beemployed, however, transformercoupling should be used betweenthe detector and output valves, or afourth valve can be introduced inthe form of an L.F. amplifier betweenthe detector and the power valve.Resistance coupling should be usedbetween the detector and the L.F.valve with a transformer between thelast two valves.

Condenser Leakage

THE source of crackling noisesin a set can generally be

located by short-circuiting the gridcircuits in turn, commencing withthe output valve. For exarpple, ifthe crackling stops when the gridcircuit of the last valve is shorted,but not when the detector gridcircuit is shorted, it can be assumedthat the defective component issituated between the detector andoutput valves. A receiver was testedin our laboratory last week, however,which proved that this reasoning isnot always correct. A very heavycrackling noise could be heaid in thespeaker which stopped iMmediatelythe detector valve was removed. Italso stopped when the L.F. trans-former windings were shorted, butcontinued after the detector grid. hadbeen disconnected from the detector -tuned circuit. This indicated a de-fective detector valve, but the sametrouble was experienced when a newvalve was fitted. The valve -holderwas next suspected, but tests indicatedthat the sockets of this were makinggood contact with the valve pins.It was eventually found that thedetector stage was quite in order,the crackling being picked up in thesame way as external interference,from a leaky modulation hum by-passcondenser in the mains unit. Theleakage was so small that it had noeffect on current consumption andvoltages, but was sufficient to pro-duce minute spark discharges whichwere picked up by the sensitivedetector valve.

August 8th, 1936

adjust thernselves to a changingworld. This should be well worthlistening to.

A Manchester LectureTHE Northern Distributors of

Ferguson receivers will hold alecture at the Midland Hotel,

Manchester, on Wednesday, Augustr2th, at 7.3o p.m., when Mr. J. B.Ferguson, who is in charge of theproduction programme of the Fer-guson receivers, will give an addresson " American methods of manufac-ture as compared with British."

Imaginary Biography : August 16th

'

MISS HELEN SIMPSON, well-known novelist, is going tothe microphone to give some

" Recollections of Dame Partington."In October, 183r, the Reverend

Sydney Smith made a speech at apolitical meeting at Taunton, inwhich he said : " The attempt of theLords to stop the progress of Reformreminds me very forcibly of the greatstorm of Sidmouth, and of the conductof the excellent Mrs. Partingtonon that occasion. . . . In the winterof 1824 there set in a great floodupon that town-the tide rose to anincredible height-the waves rushedin upon the houses. In the midst'of this sublime and terrible stormDame Partington was seen at thedoor of her house, with mop andpattens, trundling her mop, squeezingout the sea -water, and vigorously

Difficulties with the water -pipe earth.

pushing away the Atlantic Ocean.The Atlantic was roused, Mrs. Par-tington's spirit was up ; but I neednot tell you that the contest wasunequal. The Atlantic Ocean beatMrs. Partington. She was excellentat a slop or a puddle, but she shouldnot have meddled with a- tempest.Gentlemen, be at your ease-bequiet and steady-you will beatMrs. Partington."

It is of the redoubtable ladymentioned in this speech (which,incidentally, is held to have donemore for the success of the ReformBill than anything else written orspoken in England that year) thatMiss Simpson will speak.

August 8th, 1936

THE increasing activities in the ultra -short -wave band of wavelengthshas been redoubled in anticipation

of the service of signals which are to beradiated from the Alexandra Palace for thedual transmission of sound and vision. Butno matter how efficient is the radio trans-mitting or receiving apparatus, unless theaerial systems used in conjunction withthe equipment are efficient, signal strengthwill be lost and add considerably to thedifficulties of maintaining a signal communi-cation of true service value.

With the broadcast band of wavelengthsthe length of wire used for the receivingaerial proper is but a fraction of the wave-length employed, and recourse has to bemade to " loading " in order that the com-plete system may resonate to the propagatedfrequencies. In the case of ultra -shortwaves, however-that is,f those which havebeen fixed arbitrarily between the limits ofone metre and ten metres-this conditiondoes not operate. The antenna, as a rule,is made of such a length that it is a definitefraction of the wavelength used (or in somecases the average length of the range of

Fig. 1.-A good example of an aerial erectionon a roof to secure maximum height.

PRACTICAL AND AMATEUR WIRELESS 533

SHORT WAVESECTION

NOTES ON U. S. W. AERIALSThe Knowledge that the High -definition Television Signals are to be

Radiated on the U.S. Waves hasImportant One.

waves covered) without any loading in thesame sense of the word.

The DipoleConsidering for the moment the question

of television signals, and appreciating thatinterference of certain types can upsetthe resultant picture, the installation of theaerial for reception purposes becomes veryimportant if the best results are to beachieved. As in the early days of auralradio the possible number of designs aresure to be legion, but as' far as can be seenat the moment the dipole aerial is sure toloom prominently in the sphere of activi-ties. As its name infers, this aerial has alength which is almost exactly half thewavelength of the station it is required toreceive. Now, at Alexandra Palace twowavelengths are to be employed -6.67metres for vision and 7.23 metres for theaccompanying sound. These correspond tolengths of 21.9ft. and 23.7ft. respectively.If anyone desires to pick up the sound trans-missions alone, therefore, the length of theaerial proper should be between 11ft. 6in.and 12ft.,but when the dual transmissionis requird it is better to make the aerial(if only one is to be used) between 10ft. 6in.and lift. This is the length of the hori-zontal or vertical portion (see Fig. 3).Until it is stated what type of transmittingaerial is to be employed at the AlexandraPalace, it is not known whether the radiationis vertically or horizontally polarised, but,no doubt, it will be the former. If this iscorrect, then it is better to mount the aerialvertically, having it well insulated fromany form of mast support.

HeightStand off porcelain insulators are excel-

lent for this work, the insulators themselvesbeing mounted on a weathered woodenbatten so that the aerial can be hoistedon the mast to any convenient height,with the halyard attached to the batten.Porcelain cleats can also be used as shownin Fig. 2, and the aerial is made up fromheavy -gauge copper wire.

Neglecting the feeder for a moment, itis very essential to erect the aerial in ashigh a position as possible so that it isfacing the transmitting station. It isknown that ultra -short waves when radiatedtend to exhibit the same characteristicsas light waves and travel in straight linesto the point of reception. This accountsfor the necessity of height, but anothervery important factor is involved in thesame question-namely, interference. Theworst type are the radiations from theignition systems of motor -cars to whichsuppressors have not been fitted, and also

Made the Question of Aerials an

By H. J. BARTON CHAPPLE, B.Sc.

from high -frequency medical apparatus.Fortunately, the distance travelled by theseinterfering waves is, as a rule, fairly short-something of the order of 50 yards-sothat by elevating the aerial it will beremoved from the interfering zone.

The importance of this will be realised bytholse users of receiving apparatus situatednear a main road where traffic is fairlyheavy. If a mast on the roof is not possible,then it is better to have the aerial mountedon a pole at the end of the garden remotefrom the roadway. Before finally choosingthe position, the reader is advised to carryout a few interference tests, for it is some-times found that moving the aerial only afew feet is sufficient to ensure that inter-ference is reduced to a negligible quantity,the aim being, of course, to secure themaximum signal-to-noise ratio. As anexample of a well -stayed mast and aerialused for special experiments referenceshould be made to Fig. 1, for, although thesite was in a densely -populated area, the

Fig. 2.-A vertical dipole aerial supportedby porcelain cleats, and fitted with a flex feel r

534 PRACTICAL

evidence of roof tops shows that everyeffort has been made to obtain the maxi-mum height under difficult conditions.

FeedersNeXt comes the question of linking the

aerial proper to the receiving set by meansof a feeder. With the ordinary dipolethis is quite a simple matter, for the aerial

' is made up from two spans whose totallength is half the desired wavelength.These spans do not quite touch at thecentre, and to the two wire ends is joinedthe feeder. In many cases, these need onlybe heavy -gauge twisted rubber -coveredflex. Alternatively, the feeder can be lead -cased' with the lead covering earthed, whileyet another way of reducing or eliminatinginterference picked up by the feeder itselfis to use cross -over insulators throughwhich the feeder wires are' led. If lead -cased cable is employed and the aerial ison a mast at the end of the garden, it is avery good plan to bury the cable in atrench so that it emerges from the groundat a point near to where attachment tothe receiving set is to be made.

Coupling to the set is undertaken by oneor more loops which induce a magneticfield in the tuning coil of the set. In addition,for optimum results, the twin wire feedershould be made of such a length that it isan odd multiple of half the aerial length-that is, 1, 3, 5, etc., times a quarter of thewavelength being radiated.

AND AMATEUR WIRELESS August 8th, 1936

Fig. 3.-How to erectan efficient U. S. W.

aerial.

STAND OFF!NSULATORS.

A'CO UPLINGCOIL.

TWIN WIREFEEDER.

STIFF COPPER WIRE.

WOODEN BATTEN.

Signal StrengthIt is known that many important experi-

ments are being conducted with a view toincreasing the efficiency of the ultra -short-wave receiving aerial, especially from thepoint of view of reducing interferencepick-up, and once the high-powered stationhas been established at the AlexandraPalace the results of this work will soon bemade known. According to field strengthfigures which have been published fortests from other sites a signal of 1,000micro -volts is sufficient to ensure a good -quality picture., Figures lower than thiscan still give good results, but more caremay be necessary in aerial location andfeeder runs. In addition, inside dipoleaerials may be sufficient for providingadequate signal strength if the house isnot badly screened by tall trees and build-ings from the source of the radiated signal,but these points can only be settled com-pletely after the sound and vision servicehas started. In the meantime, advantagecan be taken of both the amateur trans-missions in the ultra -short-wave regiontogether with the B.B.C. test signals whichare radiated quite frequently from theaerial on the roof of Broadcasting House.

NEWNES' TELEVISION ANDSHORT-WAVE HANDBOOK

3/6 or 3/10 by post fromGEORGE NEWNES, Ltd., 8-11, Southampton St.,

Strand, W.C.2.

WEATHER conditions,although not so favour-able as they have been,

are not yet such that it is possibleto tune in on any evening a desiredstation with the full assurance ofsecuring good reception. For thisreason I have been trying out atodd times during the day andnight various sections of thedifferent bands, and although this policy ofindiscriminate searching is not one to begenerally recommended, as it happensmuch interesting short-wave informationhas been collected in this manner.

U.S.S.R.Apparently the U.S.S.R. is very rapidly

extending its broadcasts, and a furtherchannel has been added to the short-wavenetwork. On roughly 15,150 kc/s youwill find on Sundays an English talkbetween B.S.T. 16.00-18.00, RW96 on15,180 kc/s (19.76 m.), following it upwith another one at 20.30. The threewavelengths now used for these inter-national broadcasts are : 19.76 m., 19.81 m.and 31.51 m., in addition to the regulartransmissions on 25 m.

Another DX capture is HS8PJ, Bangkok(Siam), which has been broadcasting eachMonday between B.S.T. 13.00-16.00 on27.32 m. (10,980 kc/s). A correspondentinforms me that this station has also beenheard testing on 29.5 m. (10,165 kc/s), sopossibly a new channel is being tried out.

Macao, ChinaFor a really distant search it might be

worth while to attempt to tune in CQN,Macao, China, a Portuguese station reportedto be on the air every Monday and Fridaybetween B.S.T. 13.00-14.30 on 31.49 m.(9,530 kc/s), and which has been askingfor reception reports. Macao is aboutforty miles distant from Hongkong andeighty miles from Canton. Announcementsare made alternately in the Portuguese andEnglish languages. Reports should beaddressed to Senhor Joaquim P. Estrella

..MN=.11.1=4/.41=1.1

Leaves from a I1 Short-wave Log 1

de Oliveira, Administrator of Posts andTelegraphs, Macao, Portuguese China. Iam informed that " veH's " will be sentif International Reply Coupon is provided.

COCQ, HavanaA call which I have picked up on two

occasions which has greatly puzzled me isCOCQ, Havana (Cuba), as I cannot traceit in any lists. The broadcast has been onthe 31 m. band, in which so large a numberof distant foreigners are now found.Although the frequency is regularly givenout in Spanish, I have not heard it suffi-ciently clearly to translate and transcribe.I am of the opinion, however, that thismust be a new Havana short-wave outletof the . programme of a medium -wavetransmitter-possibly CMCQ, Havana. Theaddress is : Calle Vista Allegre, 90, Vibora,Havana (Cuba). I would welcome anyinformation any reader may possess orcollect regarding this station.

Costa RicaT12PG, La Voz de la Victor, San Jose

(Costa Rica), so far working on 46.99 m.(6,385 kc/s), has been lately picked up ona much higher frequency, namely, 9,565kc/s (announced), or 31.36 m., the VUB,Bombay, channel. No advice has beenreceived to the effect that a change inwavelength was contemplated. If youhear the broadcast on the new frequency,write to : Casa Victor, Apartado Postal,225, San Jose, Costa Rica.

A few days ago I was somewhat sur-prised to hear the PMN, Bandoeng (Java)programme on 15.93 m. (18,830 kc/s), as Iwas under the impression that PLE,

Bandoeng, the original possessorof this wavelength, had abandonedthe programme broadcasts forcommercial traffic. However,subsequent announcements madeit quite clear that the transmissionwas on 18,830 kc/s (announced),and I gather that the station ison the ether every Tuesday,Thursday, and Saturday for thirty

minutes from B.S.T. 16.00. The intervalsignal consists of several notes struck ongongs.

American TransmissionsNotwithstanding unfavourable weather

conditions during the past few days, broad-casts from the U.S.A. on the 19 m. bandhave been received at great volume. Thereceiver must be tuned very carefully, assince DJQ, Zeesen, on 19.63 m. (15,280kc/s), has taken to broadcast experimentallyin the early evening, very little movementof the condenser is sufficient to swampW2XE, Wayne (N.J.), relaying the Columbiasystem on 19.65 m. (15,270 kc/a). The10 -kilocycle separation is a very small one.Wayne, taking the WABC entertainments,gives out its call in about six differentlanguages. W8XK, Pittsburgh (Pa.), theKDKA short-wave outlet on 19.72 m.(15,210 kc/s), is also a powerful signal andcomes in well at dusk ; also W2XAD,Schenectady (N.Y.), acting for WGY on19.56 m. (15,330 ke/s), may be clearlyheard from about B.S.T. 16.00 until itcloses down at 20.00 B.S.T. LRU, BuenosAires, on 19.62 m. (15,290 Ws), when notswamped by DJQ can then be picked up,but as a rule it closes down before 21.00.It is an interesting portion of the bandwhich in my experience during the pastthree weeks has been singularly free fromatmospherics. Frequently when roamingaround this section of the dial you willplunge into broadcasts by amateurs, andon most nights you may log CQ calls fromfans not only in various parts of Europe,but also in the United States and SouthAmerica.


A NOVEL MIDGETA Reader's Two -purpose Unit which May be Used as a Portable Receiver

Extension Loudspeaker

THE receiver described in the followingaiticle was designed by the writerto fulfil two purposes, first, that

of a really small battery -operated loud-speaker portable receiver, and secondly,that of an extension loudspeaker to operatefrom the main family receiver.

The finished apparatus, complete with amoving -coil loudspeaker, all batteries, frameaerial, etc., measures 9_', -ins. x Slips. Xwide and weighs about 9 lbs. If a pair oftelephones are carried in the small pompart-ment provided underneath the loudspeaker,then the weight will be slightly more, ofcourse.

The receiver has a normal daylight rangeon the loudspeaker of 30 to 40 miles froma main B.B.C. station and some 80 to .100miles from Droitwich on the long -waveband, although in North-West London,Radio-Normandie, Radio -Paris and Mid-land Regional can be picked up underfaVourable conditions. After dark a numberof other stations can be received with alittle care, the writer's best log beingtwenty-six stations in half an hour !

The CircuitThe circuit, shown in Fig. 5, comprises a

conventional tuned -anode H.F. stage, fol-lowed by a detector and two transformer -coupled low -frequency stages. HivacMidget valves, types X.SG, XD and XLare used in the H.F., detector, and first low -frequency stages respectively, whilst astandard pentode such as the Hivac Y.220is used in the output stage.

A small 7 -amp. accumulator supplies thefilament current and gives about 18 hours'use per charge. The H.T. current for thefour valves is only 41 mA at 80'volts and issupplied either from the Midget batteriesnow available or, as in the writer's case, froma battery made up from small " pen torchcells, details of which are given later.

The receiver is quite stable in use providedthe various decoupling components andby-pass condensers shown in the circuitdiagram are used and the layout adheredto. It is completely free from hand -capacity

effects, which are a troublesome feature ofmost small portable receivers.

The LayoutA list of the components used is given at

the foot of the centre pages of this issue.The makes specified should be adhered to asfar as possible, as there is not much room foralterations which may be necessary if dif-ferent makes are used.

Details of the chassis are given in thediagrams shown in Figs. 1, 2 and 4,whilst a wiring diagram is given in Fig. 3.Notice from these diagrams that the loud-speaker is not quite in the centre of thechassis, although the opening for thediaphragm in the front panel is, in order tobalance the layout. The difference is slightbut important. Notice also that the frameaerial tuning condenser C6 is set back fromthe panel about lin. and is operated by anextension rod in order to avoid hand -capacity effects.

The tuned -anode condenser 07 is mountedon an Ormond tuning, dial. The latter is oneof the dual type and has a second knob,concentric with the main tuning knob,which operates the reaction condenser C5.Unfortunately this dial is' no longer astandard product, but if any difficulty isexperienced in obtaining it, then it may beomitted and the condensers C5 and C7 canbe mounted direct on the panel and operatedwith plain knobs or small geared dials. Ifthe Ormond dial is used a spacing washerof brass or ebonite, about ;tin. thick, shouldbe inserted between it and the front panel,so that the friction dial clears the rim of theloudspeaker, which it overlaps.

The positions of the three transformers,Tl, T2 and T3 are rather important andshould .not be varied. Notice that T3 hasbeen removed from the loudspeaker chassisand mounted in a vertical position with theaid of a small brass bracket, so that its coreis parallel to the panel, but at right anglesto the other two transformers.

The H.F. choke, which should preferablybe screened, is mounted underneath the

Or

coil L2, and has its axis at right angles tothe baseboard.

The pctsitions of the components havebeen chosen with a view to reducing inter-action with 'each other and also with theframe aerial to a minimum, and should beadhered to if instability is to be avoided.Only the principal dimensions of the chassisare given in Figs. 1, 2, and 4. The exactpositions. of the various parts are notcritical provided the general layout andspacing is adhered to.

The .Frame AerialIt will be observed from figures 1 and

4 that the frame aerial is wound round thechassis. The upper part of the frame -aerial support, together with its uprightswhich form the accumulator compartment,is screwed into position and the framewindings put on after the various othercomponents have been wired up.

For the medium -wave winding com-mence at the back of the chassis and puton 20 turns of 22 gauge enamelled wire inone layer, turn touching turn. Then leavea gap of about lin., and for the long -wavewinding put on about 50 turns of 30 gauged.s.c. wire, also in one layer and closelywound.

The Anode CoilThis coil, L2 in Fig. 5, is a Formo Sensity

iron -core coil which has been rewound.The base and terminals have been removedand the coil bolted to the front panelwith the aid of a small brass bracketsoldered to the base of the screening -canassembly.

Leads are taken direct from the windingsto the components concerned. Detailsof the coil windings are given below

Slot onCoil Former

Turns perSlot

Wire Remarks

1 and 2 30 Litz fromtheold coil.

Medium -wave band.

3 10 36.S.W. G. en-amelled.

Reactionwinding.

4 50 - ditto ditto5 to 9 62 38 S. W.G. en-

smelled.Long -wave

band

536 PRACTICAL AND AMATEUR WIRELESS August 8th, 1936 August 8th, 1936r4--------,-,.....-041.4141000011.=.1141-041401441.1 How. ilmo4 p=1.1.1

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Fig. 1. -Constructional details of the carrying case, showingflap to the compartment for the headphones.

The slot numbers commence from thebase of the coil former.

It will be noticed that the reactionwinding is split into two sections, in or(lerto ensure smooth reaction control on bothwavebands. No part of this winding isswitched out on either waveband however.All the windings are in the same directionand are connected as follows : The begin-ning of the medium -wave winding goesto the anode of VI, the other end goes

of the long -wave windingand also to one side of the wave -changeswitch S2. The remaining end of thelong -wave winding goes to the other sideof the wave -change switch S2. The begin-ning of the reaction winding nes to theanode of the detector valve V2', and theother end goes to the fixed plates ofthe reaction condenser .C5.

It is important to notice that the switchcontacts, S2, for the anode coil carry thefull H.T. voltage, and care should be taken,therefore, to see that the connecting wiresare well insulated. This switch is, of course,one section of the three -pole three -positionswitch referred to in the list of components,the remaining pairs of poles being switchesSi and S3.

Valve ScreensOwing to the close proximity of the

X.SG and X.D valves to the frame -aerialwindings, both these valves are fitted withcopper screening covers made from thincopper sheet. These screens are arrangedto fit tightly over the bayonet cap valveholders and are, of course, earthed. Theend of the screen for -the X.SG valveshould be left open, of course, so thataccess to the cap of the valve can beobtained, but the lead to the cap shouldbe screened with metallic braiding andalso earthed.

SundriesThe fixed condensers Cl and C2 each

consist of two .5 mfd tubular condensersconnected in parallel, as it was found thatthe .5 mfd condensers would fit into oddspaces on the chassis more easily thanthe larger 1 mfd size.

Both the L.F. transformers Ti and T2are of the R.I. parafeed type with " high -mu " cores and are quite satisfactory for

L110010,11.1.01111041.1111MH ,0Er.1/1Mr1

the drop

direct feed provided the current is limitedto a maximum of 1 mA.

It will be noticed in Fig. 3 that thetransformer Ti has the valveholder forV3 bolted to the top of the bakelite'casing.To do this it is necessary for the trans-former to be removed from the casingfirst, otherwise the drill might damagethe transformer windings. The casingof the transformer T2 has been removedin order to economise in space, the trans-former being secured to the baseboardwith clamps made from thin sheet iron.No trouble should be experienced fromlow -frequency howling, but should thisoccur, then the secondary windings of oneof the transformers should be reversed.

Using HeadphonesHeadphones can be carried in the small

compartment in the base of the cabinetformed by the space between the loud-speaker chassis and the H.T. battery asshown in Fig. 1. They are brought intocircuit with the aid of the change' -overmidget jack. The latter is wired up -so

LIST OF COMPONENTS FOR

Two .0005 " Litlos " variable condensers (GrahamFarish).

One .0002 Ormond No. 8 bakelite reaction condenser.Type R504.

Three bayonet -cap Midget valveholders (Bulgin).One five -pin baseboard valveholder (W.B.).One three -pole three -position miniature rotary

switch (Wearite).One " Formo " Sensity iron core coil (Graham

Farish). See text.Two R.I. " Parafecd " transformers.

FIXED CONDENSERS.Two .0001 mfd. tubular fixed condensers (T.C.C.,

type 300).One .0003 mfd. tubular fixed condenser (T.C.C.,

Type 300).Two .01 mfd. tubular fixed condensers (T.C.C.,

Type 300).One .1 mfd. tubular fixed condenser (T. C.C.,

Type 300).Two .5 mfd. tubular fixed condensers (T.C.C.,

Type 300).One 1 mfd. fixed condenser with tag terminals

(T.C.C., Type 65).

FIXED RESISTANCES.One 5,000 ohm half -watt (Erie).One 10,000 ohm half -watt (Erie).

that the internal loud-speaker is automaticallydisconnected when thejack is inserted.

Extension Loud-speaker

Two leads are takenfrom terminals on theoutput transformer T3, totwo small screw terminalsmounted on a strip ofbakelite at the rear ofthe chassis, so that theloudspeaker can be usedas an extension speakerin conjunction with thefamily receiver. Thetransformer is providedwith several terminals formatching purposes andthe appropriate ones

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PRACTICAL AND AMATEUR WIRELESS 537,.....!41.4=1,1141.11.1144,14MIM-1, /.4.11.1=0.1}001.1140M1141MHYONS-1

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Fig. 3.- Wiring plan of theNovel Midget Portable.

L.2.

TokeErna, Lb/4ti.fc.eEEN

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should, therefore, beselected to matchthe output of thefamily receiver.Alternatively, if it isnot intended to useheadphones, the jackreferred to abovecan be used instead.An ordinary two -spring jack will benecessary instead ofone of the change.over typo specified.Needless to say, theportable receivershould be switchedoff before attemptingextension speaker.

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Fig. 4. -Frame aerial and other important data.

to use it as an

The CaseThe case is made from any suitable

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hardwood about lin. thick, the jointsbeing dovetailed and glued together forstrength, as there is no room to use theusual blocks which would be necessarywith ordinary butt joints. The front ofthe case is of Ain. plywood, in which theloudspeaker openings, etc., are cut beforeglueing and nailing into position. Theback is also Ain. plywood and is fittedwith hinges and a small catch. If a tele-phone compartment is to be provided, itis'necessary to cut out a small trapdoor "in the base of the cabinet with a fret -sawbefore assembling the case. A simple andeffective finish (which, incidentally, hidesall traces of doubtful carpentry) is to coverthe case with black leatherette cloth asused for cameras. This can be obtainedthrough most stationers for about Is. ayard. Ordinary flour paste makes anexcellent adhesive. It should be appliedto the leatherette cloth and not to thebox. The cloth should be put on to thecase with the aid of a photographer'ssqueegee roller in order to eliminate anywrinkles or air -bubbles. A pleasant semi -glossy waterproof finish can be obtainedby applying a coat of clear cellulose varnishwhen the box is dry.

The High-tension BatteryThe Midget high-tension batteries

are now available in various, shapesand sizes and suitable units can bejoined together to provide about 80 voltsH.T. Alternatively, the latter can be madeup from pen -torch cell batteries. This isa fairly simple but rather monotonousjob. Twenty-eight fountain -pen torch

THE NOVEL MIDGETOne 25,000 ohm half -watt (Erie).One 100,000 ohm half -watt (Erie).One 3 megohm half -watt (Erie).

One H.F. choke. Disc type (Graham Farish).One 60 mA. fuse and holder (Bulgin) F5.One Midget jack and plug. Change -over type.

(B.T.S. or Igranic).One Ormond Vernier dial. Dual type (see text)

or one miniature geared dial (Ormond).Six small screw terminals (Bulgin Captive screws).

VALVES.e:X.SG, XD, XL and Y.220 (Hivac).

One 7 -amp. accumulator.One pair telephones (Ericsson). Optional.One W.B. Stentorian Speaker. Type 36M.One Midget 84 -volt H.T. battery ; (Exide " X "

series) or 28 pen -torch cells, type 6008. (See !text).

I

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SUNDRIES." Systoflex " sleeving, connecting wire, screened !

sleeving, wood for case, screws, wire for frameaerial, copper sheet for screening cans, etc. !Bakelite strip for terminal mounts. One tin.bore extension shaft coupling and short piece !of tin. rod.

MI111011MOd.411M-1101141.10.041W/0110/0.11.1,11..,..-,160.11/04=1,111=1.111/,...,

.538 PRACTICAL AND AMATEUR WIRELESS

Ht+ 45/sobatteries, such as the Exide or Drydex types,are required. These should preferablybe obtained direct from the makers inorder to ensure that they are really fresh.These batteries, when the paper wrappingsare removed, give 56 cells or about 84 volts.The brass caps of each cell should becleaned and tinned and a short length of26 gauge tinned copper wire soldered toeach zinc can. Do not be tempted tosolder this wire on to the can near theseam or the joint may " start " and allowthe chemicals inside to creep and causedamage to the other cells. The containingcase, which measures 81in. x 2fin. x 21in.wide, is made from cardboard coveredin leatherette paper. It has four compart-ments running lengthwise, formed bythree equally -spaced cardboard partitions.The fifty-six cells should be assembled inthe case and insulated from one anotherwith the usual " U " shaped cardboardspacing strips. The pieces of wire alreadyattached to the zinc cans of each cellshould be soldered to the brass cap onthe carbon of the next, taking care onreaching the end of each row not to joinup with the beginning of the previousrow and so cause a short circuit, whichwould ruin the cells in a few seconds,Tappings should be obtained by solderingon short lengths of rubber -covered flexwire to give the following voltages: G.B.44 (negative) ; G.B. if (negative) ; G.B.positive and H.T. negative (common lead) ;

L.

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August 8th, 1936

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Fig. 5.-Theoretical circuit of the Novel Midget.

H.T. positive 45 volts, and H.T. positive78 volts.

Finish off the battery by filling up withparaffin wax (melted candles of good qualitywill do) to the tops of the cells only.. Thenfit a piece of thick white drawing paperor card on top and print in black ink the

HT. -

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LT:

various voltages, etc., opposite the correcttapping points. Finally, pour a thin layerof wax over the card to fix it in position.The wax, when it sets, will be semi -trans-parent and the various voltages printed onthe card can be read through it quiteeasily.

Easy Fault -findThe next test should be to connect the

grid terminal of the holder for the outputvalve to its G.B. lead, as shown in Fig. 3.That the fault was in the output valve orthe speaker would be indicated by the factthat the crackling continued, whilst silencewould mean that the cause of the troublewas in a preceding stage. Repeat this teston other valve -holders, working " back=ward " towards 'the first valve until thelocation of the fault is determined. Thatdone, it remains to test individual com-ponents and valves, as before. When thismethod of procedure does not produce anydefinite result, a fairly good test can beapplied to the speaker by connecting it toa battery, as mentioned above, but thistime leaving both leads permanently con -

(Continued from page 527)netted for a few seconds ; crackling wouldat once point to the speaker as being atfault.

Poor Signal StrengthWeak signals call for altogether different

tests, although some assistance might begained by trying some of those alreadydescribed. In this case, however, instru-ments become practically essential, and itmight be impossible to gain any real indica-tion of the fault without taking measure-ments of voltages at the various valve -holder filament and anode terminals. Atthe same time it might be helpful to tryreplacing any resistances in the anodecircuit-coupling and decoupling resis-tances-with others of similar or not

inwidely -differing values, since one ofthese might have developed a partialopen -circuit, so reducing the H.T. voltage.Also observe the effect of short-circuitingthe H.F. choke, especially if it is foUndthat the reaction condenser has little orno effect.

The tests described are not supposed tobe conclusive, but they are definitelyhelpful, and if you find it necessary, towrite to our Free Advice Bureau, it willhelp both us and you if you state the resultsobtained. Give all the information possible,because if only vague particulars are givenwe can do no more than make suggestions ;if you state the results of your tests, we cangenerally diagnose the trouble exactly andsave your time and trouble.

Non -Standard Valvesthe type which are employed in astandard Class B Driver valve. Thusa complete Class B amplifier may bebuilt with the aid of this valve, althoughits field of. usefulness is still -further in-creased when the valve is employed inthe design of a " super one -valve "set of the type shown in Fig. 2. Here,by using the reflex principle, we canbuild with a single valve a receiver givingthe performance of a three -valve set,although naturally the efficiency will notbe quite so high and the quality will notrise to the same high level as when separatevalves are employed. However, the valveprovides some interesting lines of experimentand some novel circuits have been builtround it.

(Continued from page 528)

For Superhets OnlyThe Mazda ACHL/DDD is also a com-

bination valve consisting of three diodes anda triode, again with a common cathode.The valve is really only of practical use ina superhet receiver, where two of the diodesperform the usual function of second detec-tion and A.V.C., and the additional diode isused for noise or interstation suppression.The triode acts as the normal L.F. amplifier.Again, some interesting circuits may bebuilt round this valve, although the rangeof experiments possible is not so great aswith the previous types which have beenmentioned.

The triode-hexode and triode-octode havepreviously been marketed only by singlefirms, but are now being standardised by

other manufacturers and therefore canhardly be included in this article, but itmay be mentioned for those who have notyet come across this type of valve that it isa development of the pentagrid or heptodefrequency changer, the electrode assemblybeing in this case arranged so that the valveacts as the two separate elements of thefrequency -changing valve, the hexode oroctode carrying out the function of mixer,whilst the separate triode section acts as theoscillator. The difference between thisvalve and the standard triode -pentode liesin the fact that in the latter the couplingbetween the mixer and oscillator is carriedout by the various coils and externalcircuits, whereas in the triode-hexode thecoupling is carried out internally.


LOW -FREQUENCYA Simple Explanation of the Functionof Construction and Connection.

EVERY constructor is familiar withi L both the appearance and use of

the many types of L.F. trans -I former, but there are few who have morethan a vague idea as to its precise function.

It is, of course, used to couple one valveto another and to increase the degree -of amplification which can be obtainedfrom the valves. As all wireless valvesare what is known as voltage -operateddevices, it follows that if the trans-former is to increase the amplificationit must increase the signal voltage ;this is exactly what it does.

VOLTMETER

PRIMARY ,40,..V.11.

,11 INN

SECONDARY

CORE OF/RON

PI//lIES

Fig. I.-This shows the principle of a simpletransformer. If one lead to the primary israpidly touched against the battery terminal avoltage is developed acrcss the secondary winding.

In Its Simplest FormIn order to understand how it does it

we must consider the simplest possibleform of construction of a transformer.It consists, essentially, of an iron core 'on which are wound two coils of wire,as shown in Fig. 1. One of these coilsis called the primary, and the other thesecondary, and it is usual to wind thecomponent so that there is a greaternumber of turns on the secondary thanon the primary. Suppose, then, thatone end of the primary winding wereconnected to one terminal of a battery,the other end being rapidly touchedagainst the other terminal. If a suitablemeter were connected to the two ends ofthe secondary winding it would beobserved that a higher voltage appearedhere than that of the battery.

Theoretically, the voltage would bear thesame ratio to that of the battery as dothe numbers of turns on primary andsecondary windings. Thus, if there were500 turns on the secondary and 100on the primary, and if the battery were of3 volts, the voltage developed acrossthe secondary terminals would be 15volts. In practice the latter would beslightly lower, due to the device not beingLOO per cent, efficient.

TRANSFORMERSof these Components, their Methods

By FRANK PRESTON

More Voltage-Less CurrentIt should be explained quite clearly

that if there were permanent connectionsto the primary-instead of the con-nection being rapidly " made " and" broken "-the effect above describedwould not be observed ; in fact, therewould not be a secondary voltage at all.The transference of energy from onewinding to another is by "induction," orelectro-magnetism, and it is only whenthe primary circuit is completed or dis-connected that a voltage surge takes placein the secondary. When the circuit ismade the secondary current flows in onedirection, and when it is broken it flowsin the opposite direction. In other words,the current is what is known as alternating.Incidentally, the very same effect can beproduced by applying alternating currentto the primary winding, because this actsin just the same manner as interrupteddirect current.

The critical reader will ask how it is

SECONDARYWaVOHVG \

IRONCORE

PR/PIRRYWINDING

Fig. 2.-A usual formof construction for an

L.F. transformer.

possible that the voltage can be in-creased, since surely the transformer can-not of itself generate any electricity ? Inanswer, it can be explained that, althoughthe voltage is increased the current isreduced. Thus, if in the example men-tioned above, the primary current were1 amp. the secondary current would beonly 1/5 amp.-or rather less due toelectrical losses.

It can now be understood that if asuitably -designed transformer were takenand the primary winding connected to theoutput (anode circuit) of one valve andthe secondary connected to the input(grid circuit) of another, magnification orvoltage amplification would take place,and this is exactly what is wanted of alow -frequency transformer.

,44,4041.e ommr.o.11

Details of DesignIt remains only to consider how a i

" suitably designed" instrument can bemade. There are several methods, but a Iusual one is that shown in Fig. 2, where atwo windings are placed side by side on -insulating spools which are fitted on the fcentre limb of a set. of T- and U-shaped airon or iron -alloy stampings. First, the Eprimary winding must consist of sufficient Iturns to be of high inductance, or high aresistance to alternating currents. Thismight involve the use of 5,000 or more Iturns, which must, obviously, be of avery thin wire if they are to be accom- Imodated in the small available space. IThen the secondary winding must have a astill greater number to ensure the required

1

" step-up." It would seem that any

Fig. 3.-A divided winding spool for minimisingthe capacity of the windings.

degree of voltage increase would bepossible simply by increasing the numberof secondary turns. In fact, a ratio of a1 to 400 is quite usual in the transformerused in coil -ignition systems on motor-cars. But there are stricter limits in thecase of a wireless transformer, becauseif the number of secondary turns is madevery great the capacity between them is acorrespondingly high, the result beingthe same as that accruing from the useof a fixed condenser joined in parallel awith the secondary winding. The prac-tical limit determined by this factor isa ratio of about 1 to 7.

To use a ratio as high as this with anydegree of satisfaction great care has tobe taken to reduce the capacity of the awindings. There are different methods of -doing this, the simplest being to inter-pose strips of waxed paper or oiledsilk between every few layers of wire.Another method is to divide the windingspool into a number of sections by meansof insulating washers, as shown in Fig. 3,and another is to use one of various formsof " skeleton " former by means of

Fig. 4.-A special winding spool designed tominimise capacity.

which the winding is split up into varioussections ; see Fig. 4. It is interesting tonote, in passing, that the primary andsecondary windings may be placed either


540

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BEGINNERS' SUPPLEMENT(Continued from previous page)

side by side or one on top of the other ;Ithe effect is the same in either case.

Importance of the CoreThe designer has to consider many other

points before a good transformer can bemade. This is because the primary induc-

I

iE

ANODERESISTANCE

-0/ MFD.

G.B.=111/1.

Hr#

Fig. 5.-A small transformer can be usedi satisfactorily in the circuit shown here, becausei the primary does not have to carry any direct

(H. T.) current.

tance, and thus the number of turnsrequired to produce it, depends upon the

I size of the ferrous core and upon thej actual metal of which it is made. Generally

speaking, the same inductance can beobtained by using half as many turnson a core of twice the cross-sectionalarea, whilst the number can also be

.1 reduced by using special alloys whichare more efficient, magnetically, than

! is ordinary iron. Another importantI point is that the primary inductanceE

becomes less as the direbt current passedthrough it is increased. In fact, when more

I than a certain current is passed the trans-former is useless because the core becomesmagnetically " saturated." With anexpensive transformer-large core and

i large number of primary turns-currentsup to 7 or 8 mA may be permissible,whilst with a small, inexpensive trans-former the maximum current might beonly 2 mA.

Systems of ConnectionA method of using a small, modern

transformer effectively when the anodecurrent required by the preceding valveis comparatively' high is to connect iton the so-called parallel -feed system, asshown in Fig. 5. In this ease the directcurrent is passed through a fixed resistanceand the transformer has to deal with thealternating signal currents only, whichare passed to it through the fixed con-denser shown. A large and expensivetransformer could also be used satis-factorily in this manner, but a smalltransformer could not be used in acircuit such as that shown in Fig. 6,where the primary winding has to carrythe anode current of the valve. Thiswill explain the reason for the widevariety of prices at which transformersare sold. If, therefore, you propose touse a small and inexpensive component,connect it as shown in Fig. 5 ; if forany reason the component has to beconnected as in Fig. 6, it will pay tobuy the best transformer you canafford.

Both systems of connection can beN.T.P.

H. T. -

Fig. 6.-When using this circuit it pays toemploy a large and fairly expensive transformer.

equally effective, but the connectionsgiven in Fig. 5 involve a fairly high voltagedrop between the H.T. terminal and theanode of the valve. The other con-nections cause only a very slight loss ofvoltage, because the resistance of thetransformer primary to direct currentis not likely to exceed about 500 ohms.

L1.111111141.01W11.11.01.1.11M41.1,....01.011.11.111,410.1,1011141MENtiMIEN

NEW SOUND,RECORDING SYSTEMIN .C. STUDIOSI

THE Philips Laboratories have evolveda new method of sound recordingwhich has just been installed at the

Maida Vale studios of the B.B.C. It is anentirely new system which combines theadvantages of mechanical recording andoptical reproduction without making anychanges necessary in existing theatre equip-ment. The recording equipment has beendeveloped to a pitch of perfection which hasbeen described by experts as " perfectresponse capability."

Instantaneous playback, and directmonitoring from the finished sound -trackare only two of the important features inthis equipment. All flutter is eliminatedbecause the 17, mm. wide Philimil tape isperforated along one edge only. The actualrecording takes place on a plain untoothedroller to which the film is fed through adifferential mechanism, and the perforationsserve only to synchronise with the picturefilm.

The entire film path is visible during

recording because it is non -light sensitive,and twin heads permit simultaneous orcontinuous recording, also re-recording andduplicating. The film requires no pro-cessing whatsoever.

The Philips -Miller system has a linearresponse of 30/10,000 eye ; and a technicalline up as follows :

Philips ribbon microphones and threeamplifiers as used for public-addressequipment ;

A four -position mixing desk, for con-trol, filter networks, and meter andswitching circuits, rack mounted record-ing and reproduction amplifiers, testequipment and power supply units.The chief object in developing this system

was to utilise the obvious advantages ofmechanical over optical recording.

Of 1 Interest to Every Short -Wave Enthusiast !THE BRITISH LONG-DISTANCE

- LISTENER'S CLUBSee Neat WWI joie for en lotarestie Announcement.


The Aldershot TattooARECORD made at Aldershot during

an actual performance is ratherunique, for it has faithfully repro-

duced the roar of an aeroplane whichpassed over the arena while the massedbands of Aldershot and Eastern Com-mands, conducted by Leslie Seymour,were recording " The Lost Chord." Thisremarkable recording of " The Lost Chord "is perhaps only equalled by " With HonourCrowned "-processional march=which thebands render with considerable realism onH.M.V. C 2843.

Another record by the above bandsincludes a stirring march, " MechanisedInfantry," which is conducted by the com-poser, David McBain. A particularly finefanfare, followed by the Traditional " Min-strel Boy " and concluding with " WatchTower," which is considered one of thebest martial melodies in the Tattoo-occupythe reverse side. These three items are con-ducted by Leslie Seymour on H.M.V.B 8455.

Striking incidents of the Tattoo, includingmost of realistic " noises off," are recap-tured on two H.M.V. discs-H.M.V.C 2844/5.

" Silly Symphony "WHO has not heard of Walt Disney's

" Silly Symphonies " ? MickeyMouse fans flock regularly to the

cinema to see the latest sound cartoon byDisney. H.M.V. have now secured per-mission to record, exclusively, a series ofrecords made from the actual Walt Disney -Mickey Mouse sound films and the first ofthese is " Who Killed Cock Robin ? "-H.M.V. BD 358.

Frances Day sings two new film hits onH.M.V. BD 356. The numbers are " Apretty girl is like a melody" (from " TheGreat Ziegfeld ") and "I don't want tomake History" (from " Palm Springs ").Miss Day is accompanied by an orchestraconducted by Carroll Gibbons.

Peter Dawson's New Recording14. S. PEPPER, the composer -pianist,

wrote " The Shepherd Boy's Song,"" which Peter Dawson sings, with" A Song for you and me," on H.M. V. 8456.

The latest contribution of ReginaldFoort, organist of the Paramount Theatre,London, is a medley of catchy tunes fromthe film " The King Steps Out," onH.M. V. BD 355.

Molly Picon, a young comedy artistewho made her first record last month,makes another record this month : "A NewYork Symphony " and " What PeopleMake a Living From," on H.M.V. B 8460.

Dancing TimeROY FOX and his Band make two

excellent records this month with" A pretty girl is like a melody " and

" You " on H.M.V. BD 5082, and " Stars inmy eyes " coupled with " At the CaféContinental" on H.M.V. BD -5083. " ButDefinitely " and " When I'm with You,"two tunes from the film " POor little Rich

Girl," are Ray Noble's contribution thismonth. Al Bowlly vocalises.

Syncopation is the keynote provided by" Fats " Waller and his Rhythm in theirrendering of " It's a sin to tell a lie " and" It's no Fun " on H.M.P. BD 5087.

Dance enthusiasts, particularly those whodemand music in strict ballroom tempo,will appreciate these four new numbers byJoe Loss and his Orchestra. The titles are" The Scene Changes " and " Got to dancemy way to Heaven " on H.M.V. BD 5084 ;also " Sweetheart, let's grow old together "and " When the swallows nest again " onH.M.V. BD 5085.

The Ballyhooligans have a flair forpresenting old numbers in a new guise. Hearthem play " Tea for Two " from " No, No,Nanette "-which is being revived at theLondon Hippodrome-and " Avalon " onH.M.V. BD 5086.

Decca and Brunswick RecordsTHE Street Singer, whose records are

always popular, makes two newrecords this month. They are

" Robins and Roses " and " On the Beachat Bali -Bali "-Decca F 6012, and " All myLife " coupled with " We'll rest at the endof the Trail "-Decca F 6013.

Although only eight years old, BobbyBreen, the screen's latest discovery, makesan interesting record this month. He sings" It's a sin to tell a Lie " and " Let's SingAgain " on Brunswick 0 2246.

Grace Moore, the well-known film star,accompanied by an orchestra conducted byJoseph Pa.sternack, sings four tunes fromher new film " The King Steps Out." Theyare " What shall Remain " and " The EndBegins " on Brunswick 0 2233 and " Starsin my eyes " coupled with " Learn how tolose " on Brunswick 0 2234.

Other records just released are " Rhythmsaved the world " and " Shoe Shine Boy "by the Mills Bros. on Brunswick 0 2245," The Hills of old Wyoming " and " I don'twant to make History " by FrancesLangford on Brunswick 0 2242, and " Onthe Beach at Bali -Bali " coupled with" I met my Waterloo " by Connie Boswellon Brunswick 0 2235.

Decca Polydor RecordsALBAN BERG, who died a few months

ago, one of the most prominentpupils of Schonberg, is one of the

most adversely criticised composers of ourday by reason of the fact that he is thestaunchest exponent of what is calledatonal music. The " Lyric Suite," the firstrecorded performance of which is nowpresented on Decca Polydor CA 8244/7 isregarded as being Alban Berg at his best.

To Track That Fault-to learn howa wireless receiver works, obtain

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RaciestSportsCommen-tator

LISTENERS whotune in to Radio -

Luxembourg at noonon Sundays will have

the opportunity of hearing Bob Bowman,former ace B.B.C. commentator, give aseries of thrilling commentaries on historicsporting events.

Among the subjects to be featured in thefuture are the Dempsey-Carpentier fight,and the dramatic international footballmatch at Ibrox Park, Glasgow, on April 5th,1902, when a stand collapsed and twenty-three people were killed and 245 othersinjured.

The first broadcast in this CalvertCavalcade of Sport," as this programme isknown, took place on Sunday, July 19th,when Bowman gave a vivid picture of the1913 Derby during which a suffragettethrew herself in front of the King's horseand was killed.

Bob Bowman sprang into fame as a radiocommentator when he broadcast an eye-witness account of the Olympic Ice Hockeymatches from Garmisch early this year.His vivid and racy style made him im-mediately popular with the listeningpublic, who promptly cried out to hearmore of this enterprising young man, whosestyle is so unusually vivid.

Rathlin IslandON August 10th a programme will be

broacast from Rathlin, the lonelyisland off the coast of County Antrim. Theisland has 250 inhabitants, and traditionsays that it was here that Robert Brucesaw his famous spider. Wrecks around itscoasts have been frequent, for the Atlanticbatters against its northern shores ; and itspeople live a very primitive life, havingfew of the amenities of modern civilisation.There are no proper roads, no lighting, nopipe water supply and no industries. Gaelicis still spoken by the older people and agri-culture and fishing provide the livelihoodof the people. The programme on August10th will be a simple one, consisting ofshort interviews with some of the peoplein the island who will tell about their life.One of these will be the district nurse, whosework is lightened by the absence of in-fectious disease in the island, such diseasesas mumps and measles having never beenheard of. Communication with the main-land is carried out by means of fishing boats,and is often exceedingly difficult. The pro-gramme is being carried out by wirelesslink, and if the weather is calm there willbe- no difficulty in getting to and from theisland, but if the wind sets the wrong way itis possible that the engineers and staff mayfind themselves marooned on Rathlin.

Promenade Concerts, 1936THE B.B.C. announces that among the

artists engaged for the eight weeks'season of Promenade Concerts, whichopens at Queen's Hall on Saturday, severalwill be making their first appearance atthese concerts. In this category comesNicolas Medtner, the distinguished Russiancomposer -pianist, who will appear, on two

occasions-first on September 11th, whenhe will play the Beethoven PianoforteConcerto No. 4 in G, and again on Septem-ber 24th, when he will be the soloist in hisown Concerto in C minor. The programmeof this concert-an all -Russian one-willalso include a group of songs -by Medtner,sung by Tatiana Makushina, accompaniedby the composer.

Medtner has recently settled in London,where he has a faithful public who admirehis great gifts both as a composer, who hassomething to say in his own idiom and whois not concerned with being " modern,"and as' a pianist of the first rank. It isin this double role that he will make hisbow to the Promenade audiences inSeptember.

Another newcomer to the Proms isArthur Rubinstein, who will play JohnIreland's Pianoforte Concerto on Septem-ber 1st-a graceful tribute from an inter -

equipped with sixty-nine pianos, whichfall into three classes : those from 6ft. to7ft. 6in., from 7ft. 6in. to 9ft., and over 9ft.

All piano makers were invited by adver-tisement to submit their instruments forthe tests, which are being carried outunder conditions of strict anonymity.Neither judges nor pianists are told whichmake is under consideration.

A Two -valve Short-wave ConverterSEVERAL readers have asked for further

details of the Converter shown onpage 770 of our issue dated February 29thlast. This is a two -valve converter ofefficient design, for battery use. A penta-grid is used for frequency changing, butthe aerial circuit is aperiodic, containingonly a short-wave choke. The oscillatorcircuit is tuned in the usual way bymeans of a short-wave oscillator coil (innearly every instance an ordinary short-wave aerial coil can be used) and .00016-mfd. condenser. Parallel feed is used forthe oscillator reaction circuit, a 50,000 -ohm coupling resistance being used for H.T.supply to the anode. A Bulgin S.W. 50 I.F.coil is used with a .0003-mfd. pre-set con-denser for tuning the anode circuits of the

HOW RADIO CABINETS ARE MADE

This illustration shows a corner of the cabinet -polishing shop in the Moston Works of the Ferranticompany. The highly -finished surfaces of the Ferranti cabinets are due to the large amount of

hand labour which is employed in this particular section of the factory.

nationally -famous pianist to an outstandingEnglish composer-and the Beethoven No.3 on September 4th.

The Best Piano ?THE B.B.C. will shortly continue the

series of tests begun last month forcomparing various makes of piano underbroadcasting conditions. The last testswere carried out several years ago, sincewhen the introduction of the ribbon micro-phone and other factors have altered andimproved the transmission of music. Thenew tests will be judged by a panel drawnfrom outside expert sources and from theB.B.C. staff. Two members of the MusicAdvisory Committee will be included,while the Piano Manufacturers' Associationand the Federation of British Industrieshave been invited to nominate representa-tives. It is hoped that one well-knownpianist will also serve.

The Corporation's studios are at present

two valves, and a lead is taken to theaerial or grid terminal of the superhetthrough a .0005-mfd. fixed condenser. TheI.F. circuits suggested tune from about1,200 to 1,800 metres, and so the broadcastsuperhet must be tuned to a wavelengthbetween these two extremes. If any inter-ference is experienced at one wavelengthsetting the receiver and I.F. pre-sets can bere -tuned to another point. It will be under-stood that once the broadcast receiver hasbeen properly tuned to the frequencyprovided by the I.F. circuits of the con-verter it can be left alone, all short-wavetuning being carried out by means of the.00016 mfd. condenser in the converter.This experimental circuit is one which iswell worth trying by those in search ofhigh sensitivity and something different.'

THE CYCLIST2d. Every Wednesday

August 8th, 1936 PRACTICAL AND. AMATEUR WIRELESS 543


Club Reports should not exceed 200 words in lengthand should be received First Post each Mondaymorning for publication in the following week's issue.

The West Lohdon Radio SocietyFOLLOWING the success of the 5 -metre

river day held on Sunday, June 14th,the above radio soeiety organised a similarouting on Sunday, July 19th. The successof this meeting was even greater than thatof the previous one, the attendance beingconsiderably greater. Interesting experi-ments were made throughout the day onthe 5 -metre waveband.

Members of the society were asked toinvite their friends, many of whom cameand thoroughly enjoyed their day on theriver.

The Honorary Secretary would be verypleased to hear from anyone in the Westarea of London who is interested in anyline of radio :-H. A. Williamson, 22,Cambourne Avenue, West Ealing, W.13.

1.4={1.111,02

I BOOK RECEIVED --it HeN.04=0.0.111.111.11.4/M.O.N....li.01111101141.=.01101141101

A NEW THEORY: Inventions and Experi-ments in Wireless and Television, byD'Arcy Ford. 44 pp., 14 line illustra-tions. Published by the Author, price 1s.THIS book deals with/ some interesting

experiments carried out by the authorin relation to the detection or demodulationof wireless signals. He compares the wire-less signal with ordinary light and shows by

analogy how the splitting up of the lightray into its component colours through aprism may bedikened to the demodulationof a wireless signal. He quotes from variouspublications to show that his ideas have atleast some substantiation with moderntheories, and some of the experiments whichare given will no doubt provide interestingtopics of conversation amongst keen radioamateurs. Working circuits are shown toenable the reader to carry out trials for him-self, and they will bear out the author'sstatements. A patent has been applied forin respect of the _principle of using two ormore detector circuits as referred to in thebook, but the author makes the inventionspublic property and gives full permissionfor them to be used freely.

REPLIES IN BRIEFEt The following replies to queries are given inI abbreviated form either because of non-compliance

with our rules, or because the point raised is not ofI general interest.111,==.04/11.1.111.1.000M11100m..0.mmr041.0.M.11.1.0...114.1.1.411NA

J. S. (New Park). We can only suggest that the4 -pin coils are wrongly- wired, either to the actualpins or to the coil -holder terminals. Sometimes aresistance in the reaction circuit will help by removingparasitic oscillation.

B. L. (S.W.11.). It is very seldom that one canbuild a receiver so that the control may be set as youstate and the tuning control then adjusted throughoutthe entire range. If you will refer to our Issue datedAugust let you will see some suggestions for over-coming this trouble by ganging the controls.

A. S. (Hastings). We have no receiver with theparticular coils you mention, but they could be in-cluded in any S. G. Three type of receiver.

R. A. L. (E. 10). Send the coils back to the makersfor their test and report. It would appear that theyare wrongly connected. -

G. W. W. (H.M.S. Barham). Local conditions may bebad in the part of the world referred to, or the receiveritself may be faulty. Does the receiver get sufficient

input voltage.? An adapter cannot be connected tothe pick-up terminals, but must be used in place of thedetector stage. A converter may be joined to theaerial terminal-, and is the better proposition.

G. W. H. (Rotherham). It is impossible to comparethe two coils as there is no standard of connection. Ifyou can trace out the connections to your coil it shouldbe possible to use this to replace the coil referred to,but we cannot give you equivalent terminal numbers.The L. F. transformer will be quite satisfactory.

J. R. M. (Glenalmond). We have no particulars ofreception conditions in the Isle of Skye. We think theH. F. Pen-Det-Output circuit would be quite suitable,but do not think that either band-pass or A.V.C. wouldbe essential.

110 ILLUSTRATIONSNEW I2 PAGEBARGAIN LIST

Send for this FREE List "P" it glossdetails of a host of fine bargains.

PARCELS of experimental odd coils,magnets, wire, chokes,condensers, switches ,terminals, etc., post free:10 lbs., 7/- 7 lbs.. R/-

1,000 other Bargains in New Sale List "N."

ELECTRADIX RADIOS218, Upper Thames Street, E.C.4

'Phone: Central 4611

SHORT WAVE LISTENERSHave you seen the August issue of the "BRITISHSWL REVIEW " ? It's a SPECIAL NUMBER 1 Thismagazine, so amazingly popular with the SWLs,contains this month the circuit and description of a fineSG -V -Pen, designed by Radio G6PD. There is alsoG6LX's article "Technical Topics," all the very latestSW News, a "Blacklist," announcement, of the" Stephen Gingell " DX Contest,the popular "Amongstthe Amateurs," by R. D. Everard. Readers Calls Heard,and many other fine features. Buy your copy nowfrom W. H. Smith's, price 6d., or 61d. post free fromthe B.S:W.L., Ridgewell, Halstead, Essex.

THE PHOTOGRAPHIC HANDBOOKEdited by CONTENTS-The Art and Craft of Photography. SharpnessFRANK WITTY and in the Right Place-emulsion-Sense about l'ilters=Good,

Results with a Simple Camera-uIndoor Picture -makingG.P.KENDALL B.Sc. Mulatto° Matters-Better .POrtraita-SuocesSful. Sunset-

Choosing a- Hand Camera-The A.B.C. of Composition-Points from the " Pro "-Exposure Simply Explained-Skies, Natural and Other-Why I Prefer Plates-Experi-ment or Experience S-Winter's Opportunities-Making theMost of ColoOr.Processing Matters. A Beginner's Guide to Enlarging-TheImprovised Dark -Room, etc. -

Money -making Photography. Making Prints for Repro-ductien-NeWspaper Photographic Competitions-Printsin a Hurry-Pictures for the Press, etc., etc.

JUST OUT "Our primary aim and object inpreparing this volume has been toproduce something not merely in-teresting to read but capable ofhelping every amateur photo-grapher to make better pkturee.

"We believe it will be agreedthat the result is a really practicaland informative volume, capablenot only of inspiring the amateurphotographer with the desire toproduce better and better work,but of shovdng him how to ddthatbetter work."

316NET or 3/9 post freefrom George Nevus,Ltd., 8-11, SouthamptonStreet, Strand, W.C.2.

N EVVN ESALSO

48 C.

Airman Navy Cut, like othertobaccos in the famous Airmanrange has set an entirely newstandard in pipe -tobaccosselling at a moderate price.Quality in the leaf makes thevalue exceptional.

PLAYER'S

NAVY CUTOBTAINABLE IN MIXTURE OR FLAKE FORM

PER 0,5,

NAVY CUTDE LUXE


COMPONENTS TESTED IN OUR NEW LABORATORYNew Brimar PricesQ OME price reductions have been

effected in the Brimar range of valvesand some of the main reductions are shownbelow. These valves arc manufacturedby Standard Telephone and Cables, Ltd.,and a comprehensive catalogue dealingwith all the types, including the Tunograph,a visual tuning indication consisting of amodification of a cathode-ray oseillographtube, may be had upon request.

BATTERY VALVES4215A 10/- Pen.B 1 .. 11/-

4 -VOLT A.C. VALVES (Indirectly Heated)9/6 9A.1 .. 12/6

P.A.1 12/6 8A.1 12/615A.2 15/- 7A.2 . , 13/611A.2 12/6 7A.3 .. 13/6

4 -VOLT A.C. VALVES (Directly Heated)Peu.A.1 13/6

UNIVERSAL VALVES (A.C./D.C.)15D.1 15/- 7D.311D.3 12/6 4D.1OD.2 .. 12/6 71/68D.2 12/6 7D.8

RECTIFIERS (Universal)1D.5 10/6

RECTIFIERS (indirectly Heated)11.1 .. 10/6 11.311.2 .. .. 10/6 ' 1A.7

Bulgin Rotary Stud Switches

ASERIESof very neat switches may

be obtained from the Bulgin rangeand will be found invaluable in the con-struction of certain experimental apparatus.There are two types, one having 10 con-tacts, and the other available with either3, 4, or 5 contacts. In each type a discof bakelite has soldering tags firmly eye-letted in position round the periphery,and in the ten -contact type a furtherbakelite disc is attached and has smallportions cut away in proximity to the tags,so that the tip of the rotary contact armwill drop in and, in addition to making goodcontact, will form a positioning indicationof the " click " type. In the smallermodel holes are drilled in the bakelitedisc opposite the contacts and the end of thecontact arm is embossed, the projectiondropping into the recesses to form locationpoints. In the small model the contactarm is sufficiently wide to bridge adjacentcontacts during rotation, but in the largemodel the tip of the contact arm passesacross the overlaid bakelite disc and thusprevents short circuits. For wave -changepurposes, tone -controls, and various othersimilar pieces of apparatus these switcheswill be found extremely useful and willgive a long period of service. The 3 -way

13/69/6

13/613/6

15/-10/6

model costs Is. 6d., the 4 -way costs Is. 9d.,and the 5 -way 2s. The 10 -way type (inwhich the shaft is alive and insulatedbushes are provided for mounting purposes)costs 2s. 9d., and the contacts are silver-plated.

Vidor S.W. ConverterWE have now had an opportunity of

testing the converter which wasreferred to in our issue dated June 27thlast. This useful piece of apparatus maybe connected to the broadcast receiverand to the H.T. and L.T. batteries, andmay be instantly switched out of circuitwhen broadcast reception on the normalwavebands is required. For this purposean on/off switch is included on the side ofthe cabinet, as may be seen in the accom-

Two useful rotarystud switches manu-factured by Messrs.Bulgin. These maybe used in manyexperimental pieces

of apparatus.

panying illustration, and this automaticallytransfers the aerial connection from theconverter to the broadcast receiver. Theconverter was left connected to the broad-cast receiver during our test, and when theswitch was operated it was found thatthere was no interaction of any sort betweenthe two pieces of apparatus, and no losseswere encountered due to the leads feedingthe converter. The sensitivity was high,and the combination tested was perfectlystable throughout the entire range whilsttuning was very smooth due to theefficiently geared control knob on the con-verter.

The chart which is printed on the topof the converterwas found quiteuseful and willappeal to man yamateurs until, ofcourse, the wave-lengths of the sta-tions are changed.The scale calibra-tion in megacycles willalso be found valuablewhen amateurs are heard,or when some reference isgiven to this particularrange of frequencies andthe user cannot readilyconvert them into wave-lengths in metres, as thedial has the two types ofcalibration on the samescale. The broadcastreceiver used in the testswas adjusted to quite awide band on the long -

wave scale and the actual intermediate fre-quency was not found too critical to preventthe inexperienced amateur from finding thecorrect adjustment, whilst the manipulationof the reaction control in the receiver alsowas not too critical. It was found that itrequired to be set just off the oscillationpoint, and the exact setting may be heardin the loud -speaker just as in a simplereceiver. The calibrations on the dial weresubstantially correct. The price is 47s. 6d.complete. It covers from 13 metres to 50metres.

New Marconi-Osram TriodeTHE use of a valve for voltage measure-

ments purposes is now well known,and the valve voltmeter forms one of themost valuable pieces of test equipmentthat the service engineer can possess. Aspecial triode valve for use in such apparatushas now been produced by the Marconi -phone Company and the General, ElectricCompany, and this has a 4 volt 1 amp.heater, and is designed for a maximumH.T. of 250 volts. The 'amplificationfactor is 6 and the impedance 3,000 ohms.The type reference is A577 and the price 60s.

Hunt Interference Suppressors

ASERIESof devices for the suppression

of interference from the mains isbeing introduced by Messrs. A. H. Hunt,Ltd. These are designed for inclusion inflexible lead connectors, and for inclusionin standard apparatus, the latter modelsbeing housed in metal containers with feetfor attachment purposes. These are effec-tive on all wavelengths from 2,000 down to13 metres, and are designed for a maximumvoltage working of 250 volts. One modelis rated at 3 amps and the other at 5 amps,the prices being respectively 15s. and 21s.The lead models are priced at 2s. 6d. and5s., the smaller , model being used wheninterference is not very serious, and thelarger model when more trouble is experi-enced. Further details may be obtainedon application to the makers.

New Varley Coils

SOMEinteresting new coil units are

announced by Messrs. Varley, and theseinclude superhet ganged units and I.F.transformers. There is a 2 -gang 465 kc/sunit at 13s. 6d., and a 3 -gang 110 kc/sunit at 21s. In addition a straight 3 -gangunit comprising a band-pass filter is obtain-able at 21s. A 2 -gang straight unit costs13s. 6d. and a 465 kc/s 1.F. transformer withLitz -wound coils 'and mica trimmers costs8s. 6d. The coupling in this transformeris fixed.

The Vidor Short -wave -Converter.


LETTERS FROM READERSThe Editor does notnecessarily agree withopinions expressed by his

correspondents.

" Elf " Portable ResultsSIR, -I thought you ':may be interested

to know the results that I have gotout of the " Elf Portable " that I have justfinished making.

Using it in conjunction with my outsideaerial and earth, I can get the two localsand Paris, and sometimes Luxembourg,which I think is very good from such asmall set.

With about twenty feet of wire placedabout fifteen feet high, and the earth wiresoldered on to a nail stuck into the ground,I can get both the locals at good strength.I have also tried the set, using the springof my bed'as an aerial the results were justthe same. I bought the kit of parts fromPete -Scott, Ltd., who served me very well.I have made a few modifications to suit myown requirements : firstly, I drilled two holesin the right-hand side of the cabinet aboutone inch from the rear, so that I could screwtwo sockets into them, then I connectedthe aerial and earth leads to these sockets,then I put banana plugs on to my throw -out aerial and earth, so it is an easy matterto connect and disconnect the aerial andearth -simply plug in, then, -When finished,pull out and roll up. I have also made abox to take the accumulator ; this consistsof a box one inch high, and just big enoughto take it. I have screwed this box intothe base of the cabinet.

Also for connecting the leads to high-tension battery I have used crocodile clips,as these grip the terminals much better,and by placing rubber bands over the clipsand battery there is no fear of them touch-ing and causing a short.

I am looking forward to seeing you at theRadio Exhibition this year. -E. GA.RWOOD(Watford).

Don't Forget PostageIR,-I have just received a Q.S.L. card,

1.-.) photo, and letter from W8ANO, andby his letter it seems that a lot of amateursforget to send postage when sendingreports.

Here is an extract from his letter :-Write to some of your S.W.L. magazines

and put in a plea for S.W.L.'s to includepostage if they want answers."

I would like you to publish this in yourpaper, so that other S.W. fans, who do notsend postage with reports, will read it, andbenefit by W8ANO's letter. WishingPRACTICAL AND AMATEUR WIRELESS everysuccess. -E. BARR (Andover).

Podebrady's Wavelength

SIR,-As you report in your excellent

paper that the new Czech short-wavetransmitter at Podebrady was likely to beheard testing on a number of channelsbetween 13-50 metres, I beg to report thatI heard this station testing to -day at approx.11.15 B.S.T. Its call was " Hello ! Hello !This is Radio-Podebrady Czecho.slovakia,broadcasting and testing on a wavelengthof 19.698 metres, 15,230 kc/s. We areshortly going over to 25.51 metres, 11,760kcis." There was then a Czech announce,-ment and the transmission closed down.'

Tuning up to approx: '25 metres, I pickedup the other transmission, which wascoming in at a good R8 strength, free from

All letters must be accom-panied by the name andaddress of the sender (notnecessarily for publica-

tion).

interference. The English announcer saidthat they were actually broadcasting on11,883 kc/s, but were returning to 11,760kc/s later.. The programme, which COI -4................................... .. . .... . . .... . . T.

i A Straight Tip to Dealersii. DEAR Mr. Camm,-I have a I

postcard before me from one ofyour readers who states that he has 4

: tried six dealers -reputable wireless: dealers -to obtain a Tutor Coil andi has been told by the dealers that 1

they " cannot obtain them."This is not an isolated instance i

4 that has come to our notice ; we areI frequently receiving similar communi- f

t cations and it seems fo us to giveI the impression that the manufac- i

turers who are specified are unable i

to supply the dealers. This is, of f

g course, entirely contrary to the facts I

; and we can only assume that the so-,

4 called dealers are in some eases :

: becoming lazy and are refusing to istock or are not troubling to obtain i

i individual components from the ' :

makers. 4

; This is most, discouraging to the 4

home -constructor, who was in the I

past the mainstay of the dealer. 'This present attitude of some of I

i the dealers is a very poor return forthe constructors' support.

4We shall be pleased to hear from 4

any customer or readers who may I

make a similar complaint to you.Yours faithfully,

BRITISIL TELEVISION SUPPLIES, LTD.(Russell Scott, Sales Director). 1

CUT THIS OUT EACH WEEK.

-THAT a neon lamp may be used to constructa buzzer device for test purposes.-THAT miniature cathode-ray tubes will beseen at the Radio Exhibition, designed fortuning indicating purposes.-THAT D.C. mains receivers, giving full A.C.performance by means of a built-in D.C.-A.C.converter will also be prominent next season.-THAT a safety -spark gap in the aerial leadshould be totally enclosed to prevent leakageof signals due to dirt or wet.-THAT interference with radio receivers byvacuum cleaners may be completely removedin the near future by the introduction ofcleaners fitted with suppressor devices.-THAT a leaky electrolytic condenser can bethe source of much trouble in a mains receiver,owing to the difficulty of locating this type ofbreakdown.

The Editor will be pleased to consider articles of apractical nature suitable for publication in PRACTICALAND AMATEUR WIRELESS. Such articles should bewritten on one side of the paper only, and should containthe name and address of the sender. Whilst the Editordoes not hold himself responsible for manuscripts, everyeffort will be made to return them if a stamped andaddressed envelope is enclosed. All correspondenceintended for the Editor should be addressed : The Editor,nuentAL AND AMATEUR WIRELESS, George Newnes,Ltd., 8-11, Southampton Street, Strand, W .C.2.

Owing to the rapid progress in the design of wirelessapparatus and to our efforts to keep our readers in touchwith the latest developments, we give no warranty thatapparatus described in our columns is not the subject ofletters patent

sisted of 'gramophone records, began at08.00 B.S.T. and was ending at 20.00,and the wavelength was being changedevery half-hour.

Reports should be addressed to Radio-Podebrady, Czechoslovakia. -A. G.WILLFORD (Northanaptop).

Swedish Experimental StationSIR, -Please accept my congratulations

on the quality of your articles in yourexcellent paper. I am a' newcomer to the" Short waves " and was at first put offby the remarks of sceptical friends, but" try anything once " is one of my mottoes,and, by Jove, the short-wave pudding iswell worth the eating ! My set is an 0-v-2,home constructed, using a 45ft. horizontaloutdoor aerial. I have logged the SwedishShort-wave Experimental Station on the20 -metre band at 11.30 a.m. (G.M.T.),and should be glad to hear from any ofyour readers who heard him testing. Theaddress given is " The Swedish Short-wave Experimental Station, TechnicalUniversity, Stockholm, Sweden." -ROBERTDENNIS (Petersfield).

The One-valver AgainSIR, -I have seen published in your

pages a one-valver 40-m. log fromA. P. L. Casling, of Cheshire. Thinkingthat it might interest other readers, Ienclose my log, made up between the 13thand 18th of July. My receiver is thesingle-valver of PRACTICAL AND AMATEURWIRELESS dated March 21st, 1936.

My aerial is 45ft. on top, and a 35ft.lead-in.-STUART D. KEEBLE (Midlothian).

[This log glowed eighty-two Englishamateurs, and four Irish. -ED.]

The One -valve Short -waverSIR, -I was very interested in the

single -valve logs sent in by Mr. Caslingand Mr. Holmes, which, I believe, are thebest you have published for such sets.However, I should not be surprised to seea reader produce a log which is even better.Anyway, just to keep the ball rolling, andas you have not published a S.W. log fromLeeds, here is mine. The set, of course,is an 0-v-0, and the aerial used is 20-25ft.long, its greatest height from the groundbeing 8ft. approx.

W2XAD, W2XAF, W8XK, DJA-B-D-N-Q, TPA4, HAT4, HBL, 2R0, LKJ1,EAQ, CT1AA, RW59, and the new stationsfrom Sweden and Czechoslovakia.

20 -metre amateurs : PY2BA, PY2EJ,NY2AE, HI4F, HH2B, YOH, VO1J,VEI-CR-CD-CI, CO2KY, CO8WC ?,VP3BG, Wl-DYA-ESU-QA-AXA-CHG-MX-DIC-UH-GBE-IGX, W2-APF-HFS-ELO-BSD-GJK - EUG - CR - AMD-MJ-JOA-ICU-DH-BCR-JO-HFI, W3-DPC-MD-PC-EXC-BBB-ENF, W4AEV, W4AJA.-CnAs.WRIGHT (Leeds).

From Ireland

SIR,-As I have not yet seen a report

on short-wave reception from thisdistrict, I beg to offer mine, as follows :-

On loudspeaker : CT1AA, CT1AH, DZH,EAQ, EI3J, F8DC, F8II, HB98, IDU,LAIG, OZ1D, ORK, PCJ, PHI, PY2EJ,RKI, RW59, SU1CH, SU1RO, SU1SU,SM5SX, SPW, W1XAL, W2XAF, W2XAL,W2BSD, W8XK, WQP. Most of theZeesen, Daventry, Radio -Colonial (Paris)stations and both the 12R0 transmitters.

Also : A score or so " " stations-EA7AI, HI4F, W-1ARC, lACQ, 1GED,1DAL, 1DSM, II1 D, 1SZ, 2AKK, 2ICU,2KR, 9DB, 9CLIT. Average R3-6.

These were all " bagged " on an 0 -v -Pen.-T. L. FOLLEY (Cork).


Practical and Amateur WirelessBLUEPRINT SERVICE

PRACTICAL WIRELESSSTRAIGHT SETS. Battery Operated.

One -valve : Blueprints, Is. each.Dote of Issue. No. of

BlueprintAll -Wave Un!pen (pentode) .. PW31A

Two -valve : Blueprints, 1s. each.Four -range Super Hag Two (11,

Pen) _

Three -valve : Blueprints, 1s. each.Selectone Battery Three (D, 2 LF

(trans.)) _Sixty -Shilling Three (1), 2 LF

(R.C. K trans.)) ..Leader Three (SG, D, Pow.) ..Summit Three (HF Pen, 1), Pen)All -Pentode Three (HI' Pen, D

(pen.), Pen)Hull -Mark Three (SG, D, Pow.)Hall -Mark Cadet (H, LF PenF. J. Camm's Silver Souvenir (Hi

Pen, 1) (pen), Pen) (All -WaveThree) .. .. 13.4.35

Genet Midget (D, 2 LF (trans.)). .June '35Cameo Midget Three (1), 2 LF

(trans.)) .. 8.6.351936 Sonotone Three -Four (HF

Pen, HF Pen, Westector,Pen) .. .. 17.8.35

Battery All -Wave Three (D, 2 LF(11.0.)) 31.8.35

The Monitor (HF Pen, D, Pen)*

. 8.2.36The Tutor Three (HF Pen, D, Pen) 21.3.36The Centaur Three (SG, D, P)

Four -valve : Blueprints, Is. each.Fury Four (2 SG, I), Pen) ..Beta Universal Four (SG, D, LF,

Cl. B)Nucleon Class B Four (SG, D

(SG), LF, CI. B)Fury Four Super (SG, SG, D, Pen)Battery Hall -Mark 4 (HF Pen, 1),

Push -Pull)

11.8.34 PW3013

2.12.33

18.8.34

22.9.34

Mains Operated.Two -valve : Blueprints, ls. each.A.C. Twin (D (pen), Pen)A.C.-D.C. Two (SG, Power) .. 7.10.33Selectone A.C. Radiogram Two

(I), Pow.)

16.3.35

15.4.33

6.1.34

Three -valve : Blueprints, Is. each.Double -Diode -Triode Three (HF

Pen, D.D.T., Pen) .. .. 10.6.33D.C. Ace (SO, D, Pen) .. .. 15.7.33A.C. Three (SG, D, Pen) .. .. -A.C. Leader (HF Pen, D, Power) 7.4.34D.C. Premier (HF Pen, D, Pen) 31.3.34Ublque (HF Pen, D (Pen), Pen) .. 28.7.34Armada Mains Three (HF Pen, D,'

Pen) .. 18.8.34F. J. Camm's A.C. A11 -Wave Silver

Souvenir Three (HF Pen, I),Pen)

"All Wave" A.C. Three (1),

A.C. 1936 Sonotone (1W Pen, Rh'Pen, Westector, Pen) ..

Four -valve : Blueprints, 1s. each.A.C. Fury Four (SG, SO, D, Pen)A.C. Fury Four Super (SG, SG, D,

Pen) ..A.C. Hall -Mark (HF Pen, D, Push -

Pull)Universal Hall -Mark (HF, Pen, 1),

Push-pull) 9,2.33

11.5.35

17.8.35

31.8.35

SUPERHETS.Battery Sets : Blueprints, is. each.£3 Superhet (Three valve)F. J. Camm's 2 -valve Superhet

(two -valve) .. 13.7.35F. J. Camm's £4 Superhet

Mains Sets : Blueprints, 1s. each.A.C. £5 Superhet (three -valve) ..D.C. £5 Superhet (three valve) .. 1.12.31Universal £5 Superhet (three

valve) .. .. .F. J. Camm's A.C. £4 Superhet 4If. J. Canon's Universal £4 Super -

11.1.30

SHORT-WAVE SETS.Two -valve : Blueprints, 1s. each.Midget Short -Wave Two (D, Pen)

Three -valve : Blueprints, ls. each.Experimenter's Short-wave Three

(SG, D, Power) ..The Prefect 3 (I), 2 LF, RC and

'Trans.)

15.9.34

_8.2.36

PWIO

PW34APW35PW37

PW39PNV41

PW48

PW49PM2

PW51

PW53

PW551'W61PW62PW64

PW11

PW17

PW34BPW34C

PW46

PW 18PW31

PW19

PW23PW25PW29

PW35CPW35BP1V36A

PW38

PW50

PW54

PW56

PW20

PW34D

PW45

PW47

PW40

PW32P W 38

PW 13P W 42

P\V44PW59

PW60

PW3SA

PIV30A

PWG3


Portable (Hit Pen, 1), I'eu)

Four -valve : Blueprints, 1s. each.Featherweight Portable Four (Slit,

ll, LF, Cl. B)

MISCELLANEOUS.S.W. Converter -Adapter (1 valve)

16.5.36 PW65

PW12

PW4SA


Blueprints, 6d. each.Four -station Crystal Set .. - AW4271934 Crystal Set .. _ - AW444150 -mile Crystal Set .. - A Vi'450

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, Is. each.B.B.C. Special One-valverTwenty -station Loud -speaker


Two -valve : Blueprints, Is. Sach.Melody Ranger Two (D. Trans)Full -volume Two (SO., Det., Pen)B.B.C. National Two with Lucerne

Coil (D. Trans)Big -power Melody Two

Lucerne Coil (SG, Tram)Lucerne Minor (D. Pen) ..A Modern Two-Valver

AW387

AW449

AW388A W392

- AW377Avet ft; - AW338A

AW426:: July '36 WM409

Three -valve : Blueprints, le. each.Class -B Three (D, Trans, Class B) 22.4.33 AW386New Britain's Favourite Three

(D, Trans, Class B) .. 15.7.33 AW394Home -Built Coil Three (SG, D,

'Trans) - AW404Fan and Family Three (D, Trans,

Class B) 25.11.33 AW410£5. 5a. 8.0.3 (SG, 0, Trans) .. 2.12.33 A W4121934 Ether Searcher: Baseboard

Model (SG, D, Pen) 20.1.34 AW4171934 Ether Searcher: ChassisModel (SG, D, Pen) ..- AW419Lucerne Ranger (SG, I), Trans) A W422Cossor Melody Maker with Lucerne

Coils AW423Mascot wilt* Lucerne Con; -

(D, RC, Trans) .. - AW337AMullard Master Three with

Lucerne Coils . - AW424£5 5a. Three : De Luxe Version

(SG, D, Tram) - . 19.5.31 AW435Lucerne Straight Three (D, RC;

Trans) .. _ - AW437All Britain Three (HF Pen, D,Pen) - AW448" Wireless League " Three (HF

Pen, D, Pen) .. . 3.11.34 AW451Transportable Three (SG, ll, Pen) - W5f271£6 es. Radiogram (I), RC, Tram) - NV -51318Simple tune Three (SO, D, Pen) June '33 WM327Economy -pentode Three (SG, D,

Pen) . Oct. '33 WM337" W.M." 1934 Standard Three

(SG, D, Pen) - W51351£3 Ss. Three (SG, D, Trans) .. Mar. '31 WM354Iron -core Band-pass Three (SG, D,

QP21) . June '34 WM3621935 £6 Os. Battery Three (SG, H,

Pen) WW51371..-P.T.P. Three (Pen, D, Pen) .. June '35 WM389Certainty Three (8G, D, Pen) Sept. '35 WM393Minitube Three (SG, I), Trans) .. Oct. '35 WM396All -wave Winning Three (SO, ll,

Pen) .. Dec. '35 WM400

Four -value : Blueprints, is. Eld. each.65/- Four (SO, 1), RC, Trans) .. - A W370" A.W." Ideal four (ISO, I), Pen) 18.9.33 A W4022 H.F. Four (250, ll, Pen) - AW4:21Crusaders' A.V.C. 4 (211F, D,

QP21) .. 18.8.34 A W445(Pentode and Class -B Outputs for

above : blueprints 6d. each) .. 25.8.34 AW445ASelf-contained Four (SG, D,

Class II) Aug. '33 W51331Lucerne Straight Four (SG, D, LF,

Trans) - WM350£5 5s. BatteryFour (HF,

2LF) .. Feb. '35 W51381The B.A. Four . Mar. '53 WM384The Auto -Straight Four .. April '35 WM404The Request All -Waver .. June '36o WM407

Five -valve : Blueprints, ls. 6d. each.Super -quality Five (211F, D, RC,

Tram) . May '33New Class-B Five (2SG, *D,

Class B) . Nov. '33Class -B Quadradyne (2SG, D, LF,

Class B) . Dec. '331935 Super Five (Battery Super-

WM320

W5I340

WM344

W 51379 .

August 8th, 1936

These blueprints are full size. Copies of appro-priate issues containing descriptions of these setscan in most cases be obtained as follows :-" Practical Wireless " at 4d., " Amateur Wire-less " at 4d., " Practical Mechanics " at 70., and" Wireless Magazine " at 1/3d., post paid. Indexletters " P.W." refer to " Practical Wireless "sets, " P.M." to " Practical Mechanics " sets," A.W." refer to " Amateur Wireless " sets, and" W.M." to " Wireless Magazine" sets. Send(preferably) a postal order (stamps over sixpenceunacceptable) to "Practical and Amateur Wire-less " Blueprint Dept., Geo. Newnes, Ltd., 8-11,


Mains Operated.Two -valve : Blueprints, 1s. each.Consoeleetric Two (D, Pen) A.C. 23.9.33Economy A.C. Two (IL Trans) A.C. -Unicorn A.C./D.C. Two (II, Pen) Sept. '35Three -valve : Blueprints, Is. each.Home -lover's New All -electric

Three (SO, 1), Trans) A.C. -8.0. Three (SO, 1), Pen) A.C. -A.C. Triodyne (SG, D, Pen) A.C. 19.8.33A.C. Pentaquoster (HI' Pen, D,.

Pen) A.C. .. 23.6.34Mantovaiii A.C. Three (HF Pen,

1), Pen) A.C. . -£13 15s. 1936 A.C. Radiogram

(HF, D, Pen) .. Jan. '36Four -valve : Blueprints, ls. 6d. each.All Metal Four (2 SO, D, Pen) .. Judy '33 WM329Harris Jubilee Radiogram .. May '35 WM386

SUPERHETS.Battery Sets : Blueprints, ts. 6d. each.Modern Super Senior - W H375Varsity Four Oct. '35 WM395Mains Sets : Blueprints, Is. 6d. each.1934 A.C. Century Super A.C. 10.3.34 A W425Heptode Super Three A.C. .. May '34 WM359" W.31." Radiogram Super A.C... - WM3661935 A.C. Stenode- Apl. '35 W31355

A W403WM286WM394

AW383AW390AW399

AW439

WM374

WM-401

PORTABLES.Four -valve : Blueprints, ls. 6d. each.Midget Class B Portable (SG, D,

LF Class B) 20.5.33Holiday Portable (8G, D, LF,

Class B) . 1.7.33Family Portable (HF, D, RC,

Trans) .. 22.9.34Two H.F. Portable (2 SG, D*,

QP21) . .. June '34Tyera Portable (SG, D, 2 Trans) Aug. '34

A W389

A W393

AW447

WM363W51367

SHORT-WAVERS-Battery Operated.One -valve : Blueprints, ls. each.S.W. One -valve converter (price 6d.) - AW329S.W. One -valve for America - AW429Horns Short -waver - AW452Two -valve : Blueprints, ls. each.Ultra -short Battery Two (SG det,

Pen) .. .. Feb. '36 W51402Home-made Coil Two (D, Pen) A W440Three -valve : Blueprints, la. each.World -ranger Short-wave 3 (D,

RC, Trans) - A W335Experimenter'slran e5g- me r e Set (D,

30.6.34 A W438Experimenter's Short -waver ..Jan. 19, '35 AW493The Carrier Short -waver .. July '35 WM390Four -valve : Blueprints, is. 6d. each.A.W. Short-wave World Beater

(HF% Pen, I), RC, Trans) . - AW436Empire Short -waver (SO, D, RC*,

Tram) .. - W51311Standard Four -valve Short -waver Mar. '35 W51333Superhet : Blueprint, Is. 6d.Simplified Short-wave Super .. Nov. '35 W11397

.Mains Operated.Two -valve : Blueprints, is. each.Two -valve Mains Short -waver (D,

l'en) A.C." W.111." Band -spread Short -waver

(D, Pen) A.C./D.C. Aug. '34" W.M." Long -wave Converter .. -

Three -valve : Blueprint, 1s.Emigrator (SO, D, Pen) A.C.Four -valve : Blueprint, ls. 6d.Standard Four -valve A.C. Short -

waver (SG, 1), RC, Trans) .. Aug. '35 W51331MISCELLANEOUS.

Enthfisiast's Power Amplifier (1/6) June '35 W51387Listener's 5 -watt A.C. Amplifier

(116) .Sept. '35 WM392.Radio t (I or 39 ) Nor. '35 WM398Harris Electrograin (battery am-

plifier) . Dec. '35 WM399De -Luxe Concert *A.C. Electro-

gram .. Mar. '38 W11403New style 'Short-wave Adapter

(110 June '35 WM388Trickle Charger (6d.) Jan. 5, '35 AW462Short-wave Adapter .. Dee. 1, '34 AW456Superhet Converter ' . . Dec. 1, '34 AW457B.L.D. L.C. Short -Wave Converter

( Is.) May '36 WM405,Wilson Tone Master (Is.) . June '36 WM406The W.M. A.C. Short -Wave Con-

verter (is.) Jut,/ '36 WM498,

AW453

WM30,3W M380

W51352


_QUERIES 6414

_ENQUIRIES

A Change of Address" I have a straight three set and I have

moved to another house, about a milefrom my old address and higher up on thehill. I used to be able to get foreignersquite easily, but now I can only get thelocal station. Could you let me know thecause of this trouble and how I could rectifyit? "-M. P. (Walton -on -the -Hill).

AS the receiver originally worked satis-factorily, and provided that no

damage has been sustained during themove, it may be regarded as not responsiblefor the failure now to get the distantstations. Therefore,' the cause of thetrouble must be your new aerial -earthsystem or the particular atmospheric orphysical conditions of the new, district.Firstly, we suggest you endeavour toerect the new aerial in the same directionas the original one as this may play quitean important part. Secondly, endeavourto improve the earth connection, and trydifferent types of earth in case the soil isof a different material in the new place.Finally, inquire of local people or a localdealer and find out whether the type ofset you are using gives good results in thisparticular part.

A One-valye Set." I want to construct a one -valve set,

and should be glad to receive details of theone -valve sets you have designed. I amonly eleven years of age, and should likesomething simple."-D. N. B. (Felsted).

YOU will see from the Blueprint Servicelist on page 546 that we can supply

three blueprints for standard types of one -valve set, and three blueprints for short-wave one -valve sets. You should thereforedecide whether you require a short -waveror a broadcast set, and also whether youwill buy ready-made coils or make yourown. In the case of the short wavers allthe coils are home-made, but in the broad-cast sets only one utilises a home-made coil.The most powerful of the broadcast one-valvers is the twenty -station loud -speakerone-valver, but this employs a special dualvalve, and is, in effect, a detector push-pullset using the reflex principle. The All -waveUnipen employs a pentode valve, but coversthe short-wave in addition to the broad-cast wavebands.

Winding a Soldering -iron" I have made a very useful size soldering -

iron, complete with a full tin. hole boreddown its centre. Having tried several piecesof resistance wire for an element, and blownequally as many fuses, I have come to theconclusion that I had better seek youradvice. My ambition is to wind an elementon a former about 2in. long by tin. to *in.diameter, thus allowing for a covering ofmica to make a snug fit into the bit. Ishould like to attain a soldering heat withas Tow a consumption as practicable;supply 280 to 250 volts, 50 cycles."-E. C. J.(West Croydon).

A8 the iron is apparently a small one,a loading of about 45 to 50 watts

should be ample, and could not be con-

LI111141.1.41.1.1/.111N

sidered too expensive to run. Youwould need for this approximately800 ohms resistance running atapproximately a quarter of an amp.

A suitable gauge of nickel chrome wire togive a temperature of 400 deg. C. at thisrating would be No. 40, and for the totalresistance mentioned you would need ap-proximately 100 yards. The wire is veryfine, and you should be able to ac-commodate it in the space mentioned, anyexcess space being filled up with asbestosstring as a packing.Increasing the Output

" I built the Wireless League 3 abouteighteen months ago and am very pleasedwith it indeed. The present output is abouthalf a watt, from a Cossor P.T.2 pentode,

r----,-__IMIWO.=41.111=.0411M1.01RULES

We wish to draw the reader's attention to thefact that the Queries Service is intended onlyfor the solution of problems or difficultiesarising from the 'construction . of receiversdescribed In our pages, from articles appearingin our pages, or on general wireless matters.We regret that we cannot, for obvious reasons-

(1) Supply circuit diagrams of completemulti -valve receivers.

(2) Suggest alterations or modifications ofreceivers described in our contem-poraries.

(3) Suggest alterations or modifications tocommercial receivers.

(4) Answer queries over the telephone.(5) Grant interviews to querists.

Please note also, that queries must be limitedto two per reader, and all sketches and draw-ings which are sent to us should bear thename and address of the sender.If a postal reply is desired, a stamped addressed envelopemust be enclosed. Send your queries to the Editor,PRACTICAL AND AMATEUR WIRELESS, GeorgeNewnes, Ltd., 8-11. Southampton Street, Strand,

London, W.C.2.

Si

but I should like about 1 watt from thesame set without adding another valve.My H.T. is obtained from an eliminator,so that I need not worry about that. If youcan tell me of another valve could youalso tell me what value resistance I shallneed, as I have an automatic grid bias ? "-R. B. (Sherborne).

THE P.T.2 is a Marconi-Osram valve,not a Cossor, and we presume you

have simply given the wrong maker's name,and not the wrong reference type numberof the valve. However, an output of1,000 mW (1 watt) is given by the Cossor220PT, and 230PT, the Hivae Z220, theLissen PT240 and PT2A, the Mazda Pen220A, the Mullard PM22C, and the 362Valve Company's ME2 and ME2A. Youcould, therefore, ,use any of these valves,and Will find that the filament consumptionwill vary with different valves from .1 to .3.The bias resistor will also vary with in-dividual valves in view of the differencesin anode current, and, therefore, you shoulddecide upon the valve, and the maker's datasheet will give the anode current and gridbias, from which the value of the resistormay be ascertained by dividing the voltageby the current in milliamps and multi-plying by 1,000.

Break -through" I have a home-made three-valver in

which the majority of the parts have beenmade by hand, and although results are verygood indeed there is one difficulty which Ihave not been able to overcome. At

practically every part of the dial it is possibleto tear the local station faintly, and it doesnot seem as if this will tune out. The tunedcircuits are quite all right, as I can getdozens of foreigners. Is there any reasonwhich you can suggest for the trouble anda suitable cure, or is it some local peculiar-ity ? "-F. C. (Walthamstow).

THERE are one or two suggestions whichwe can make, but we think that the

trouble is quite definitely due to break-through owing to some part of the completeequipment resonating at the particularfrequency of the interfering station. Thismay be the actual aerial -earth system, oneof the coupling coils in the circuit, an H.F.choke, or some similar circuit. If you havewound the tuning coil with an aperiodicaerial coil, or an H.F. transformer with anunlined primary winding, this may be thesolution, and may be verified by connectinga condenser across it so that it may betuned to a high wavelength (together withthe secondary) in order to confirm that thestation is eliminated on that particularwavelength. You can test the chokeseither by removing them entirely andusing resistors in their place, or by substitut-ing different windings.

Faulty Padding Condenser" I have been using the £4 Superhet,

but now cannot get satisfactory results onthe long waves. I have spent hours tryingto get this ganged satisfactorily, and I canget Droitwich, but the padding condenserdoes not make the slightest difference. Isit possible to do this any other way ? "-C. E. (Howgate).

ALTHOUGH there may be a possibilityof faulty matching in the coils or

I.F.s, we note that you have spent hourstrying to gang the receiver, and thereforethere is a possibility that the paddingcondenser has been damaged. These com-ponents function by means of a springyplate which is depressed when the screw istightened, and if you have repeatedlyscrewed and unscrewed this adjustment,the plate may be remaining now in themaximum position and not returning whenthe adjuster is unscrewed. Try anotherpre-set, and if you still cannot gang thecircuit, it would be advisable to have thecoils tested.

The Best Detector" I should like to fit to my receiver the

very best type of detector, and do not knowwhether the diode is best, or the power -grid. Perhaps you can help me to make adecision ? "-P. H. (Crewe).

WHEREVER possible, that is to say,where ample pm -detector amplifica-

tion is available, use a diode detector byreason of its distortionless operation, Ifdiode detection is impracticable, use agood power -grid detector. For maximumresults for a minimum expenditure ofbattery power, use the conventional leaky-grid detector, keeping the anode voltageat the lowest value which provides sufficientreaction, if reaction is used.

The coupon on page 548 must beattached to every query.

1

COPTSTRUCTOR'S ENCYCLOPEDIABy F. J. CAMM 4th /

(Editor of " Prociteal and Amateur UEdition 0/- net.Wireloto)Wireless Construction. Terms and Definitionsexplained and illustrated in concise, clear

language.From all 'Booksellers, or 15 post 516 from GeorgeNewnes, Ltd., 8-11, Southampton Street, Strand.

London. W.C.2.


Miscellaneous AdvertisementsAdvertisements are accepted for thesecolumns at the rate of 3d. per word. Wordsin black face and/or capitals are chargeddouble this rate (minimum charge 3/- perparagraph). Display lines are charged at6/- per line. All advertisements must beprepaid. All communications should beaddressed to the Advertisement Manager." Practical and Amateur Wireless,"8, Southampton Street, Strand, London.



RADIOMART (MUSHORT-WAVE SPECIALISTS


RADIOMART. Utility 2 -gang uniknob and dial,3/11, 1,500 vt. Tubular condensers, 6d. ; Helsby

electrolytics 8 inf. 500, 2/11, 4 x 4 mf., 1/6, 25 mf.,25 v., 1/- etc.

RADDAIART. Smoothing chokes,20 by 120 ma.,3/11 ; 100 ma., 2/11 ; 40 ma., 1/11. Telsen Ace

transformers, 1/11. Radiogrands, 11048, 2/9. BTHspeaker, 2/11.

RADIOMART. Varley Iron -cored, 10/6. Bifocaldual -range coils. Very selective, 2/11 ; matched

pair, 5/3.RADIOMART. Pushbaek wire 6 'yds. 6d heavy

; 2 gross solder tags, Gel. Resincored solder,Oft., Gd.DADIOMART, Centralab pots, all sizes, 1/0;.1.1, switched, 2/-. Tubular glass fuses, 2d.

RADIOMART. Igranic midget jacks, 3d. Minim -meters, 25 ma. upwards, 5/0 ;-super 6/9.

D ADIOMART. Telsen H.F. chokes, 1/11 ; screened11 1/11. Utility 1936 SL wavelength dials, 3/11.

RADIOMART. Lissen 3 -gang superhet kit coils,two I.F.'s ganged condenser, ditto Bandpass,

ditto 2 -gang all wave, 10/- kit.RADIOMART. Traders' monster bargain parcels,

value £4/10/0 for 10/-; also 5/- parcels.RADIOMART. Famous continental A.C. valves,

4/6. American Durtron, etc. All types, 3/6.Battery from 2/3.

RADIOMART. Utility 8/6, microdisc dials, 3/11.Radiophone .00016 short-wave condensers, 3/6.

Series gap twin, 3/9. -

RAMOMART.Ceramic all brass microvarlables,

15 mmfd., 1/4. 40 mmfd., 1/7. 100 mmfd., 1/10.Short-wave MEC., 9d.

ADIOMART. Orders 5/- post free. Get our bar-n, gain catalogues. General, lid. Short-wave, lid.44, Holloway Road, Birmingham. Tel. : MID 3254.

ALL goods previously advertised are standardlines, still available. Post card for list free.

/AUXHALL UTILITIES, 163a, Strand, W.C.2.V Over Denny's the Booksellers. Temple Bar

9338.

CONVERSION UNITS for operating D.C. Receiversfrom A.G. Mains, improved type, 120 watts

output, at £2110/0. Send for our comprehensive list ofspeakers, Resistances and other components.WARD, 46, Farringdon Street, London, E.C.4.

Telephone: Holborn 0703.

ALI, lines advertised last week still available.RADIO CLEARANCE, 63, High Holborn,

W.C.1. Tel.: Holborn 4631.

LOUDSPEAKER REPAIRS

D EPAIRS to Moving Coil Speakers, Cones and Coils11 fitted or rewound. Fields altered. PricesQuoted including Eliminators, Loud -speakers Re-paired, 4/-. L.F. and Speech Transformers, 4/- postFree. Trade Invited. Guaranteed. Satisfaction.Prompt Service. Estimates Free. L.S. Repair Ser-vice, 5, Balham Grove, London, S.W.12. Battersea1321.

NEW RECEIVERS, COMPONENTS,AND ACCESSORIES

ULBERT for Quality Surplus Speakers. AllMusic Lovers should write for List of amazing

bargains. Prices from 8/6 brand new. Made by bestknown British maker.-Hulbert, 6, Conduit Street,W.1.


Brand new stock with six months' guarantee. 2 voltDetector, 2/3, Power 2/9, Screen Grid, Pentode, H.F.Pentode, 5/-. The following American type valves,fully guaranteed, at 5/6 each : No. 80, 42, 43, 57,68, 77, 78, 6C6, 6D6, 25Y5, 25Z5. Write for otherprices to : Dulci Electrical Co., Ltd., 7, Lizard Street,London, E.C.1.



S.W.4. (Macaulay 2381)and 165 and 165a, Fleet St., E.C.4 (next toAndertons

Hotel). (Centra12833.)NOW READY ! Send 4d. in stamps for NEWILLUSTRATED GIANT CATALOGUE AND VALVE

LIST.

SHORT WAVES.SHORT-WAVE COILS 4 to 6 -pin types. 13-26,

22-47, 41-94, 78-170 metres, 1/9 each withcircuit. Special set of 3 S.W. Coils, 14-150 metres,4/- with circuit'. Premier 3 -band S.W. Coil,11-25, 19-43, 38-86 metres. Simplifies S.W. re-ceiver construction, suitable any type circuit, 2/-.

COILFORMERS, in finest plastic materials,

1/in. low -loss ribbed 4- or 6 -phi, 1/- each.nONDENSERS, super ceramic S.L.F. .00016,If .0001, 2/9 each; double-spaced .000015,.000025, .00005, 3/- each. All brass with integralslow-motion .00015 tuning, 3M .00015 reaction,!/S.SHORT-WAVE KIT for 1 valve receiver or

adaptor, complete with chassis, 3 coils 14-150metres, condensers, circuit, and all parts, 12/6.VALVE GIVEN FREE.2 -VALVE S.W. KIT, complete with valves, 19/6.

3VALVES.W. KIT, S.G. Det. and Pen., complete

with valves, 40/-.BAND PASS KIT, 14/8 the lot. Lissen 3 -gang

coil unit. Utility 3 -gang condenser anddisc drive 4 valve -holders, chassis and blue -print..RUPERHET KIT, 15/6 the lot. Telsen Band-

Pass/0 Superhet Coils, I.F.'s, 3 -Gang Condenser,Disc Drive and chassis.SPEAKERS, K.B. 8" P.M.s 9/8, Goodman 7"

P.M.s, 9/6, Rola 7" P.M.s, 10/-.MAINS TRANSFORMERS. Premier wire -end

type with screened primaries.H.T.8 & 9 or H.T.10 with 4v. 4a C.T. and 4v. la.C.T.; 8/6.250-250v. 60 m.a., 4v. la., 4 v. 2a. and 4v. 4a., allC.T., 8/6.350-350v. 120 mac, 4v. la., 4v. 2a. and 4v. 4a.,all C.T., 10/6.500-500v. 150 ma., 4v. 2-3a., 4v. 2-3a., 4v. 2-3a.,4v. 3-4a., all C.T., 19/6.Any of these transformers with engraved paneland N.P. terminals, 1/6 extra.AUTO TRANSFORMERS, step up or down,

00 watts, 7/6, 100 watts, 10/,MAINS VALVES, famous Europa 4v. A.C.

types, 4/6 each. H.L., L., S.G., Var.-Mu-S.G. H.F.-Pens., Var.-Mu.-H.F. Pens, 1, 3,and 4 -watt LC. directly -heated output Pentodes.Full -wave rectifiers, 250 v. 00 ma. A.C./D.C.types, 20 -volt .18 amp. B.G., Var.-Mu-S.G., H.,H.L., and Power.Following Types all 5/6 each. Full -wave rectifiers350v. 120 ma. and 500 v. 120 m.a. 2} watt. In-directly -heated Pentodes. Frequency Changers.Octodes and Heptodes.RATTERY -VALVES. 2 -volts, H.F., L.F., 2/3.B

Power, Super -Power, 2/9. S.G., Var.-Mu-S.G., 4 or 5 -pin Pentodes, H.F. Pens., V. -Mu -11.F. .

Pens., 5/-. Class B, 3/6.AMERICAN VALVES. Genuine American1,1 DUOTRON, all types, 3/6 each. Hytronsuper quality, 3 months' guarantee, all types, 5/5.MILLIAMRETERS, moving -iron flush 21",

all ranges from 0-10, 5/9. Visual tuning,6 or 12 ma., 5/-. Moving coil meters, 21" 0-1 m.a.,18/6; 31" 0.1 ma., 22/8. Multipliers, 1/- each.Westinghouse meter rectifiers, 17/6 each.E LECTROLYTICAL U.S.A. 4, 8 or 12 mfd. 520 v.8. peak, 1/9 each. Miller, 4 or 8 mfd. 500 v.,3/. ; 50 mfd. 50 v., 1/9 ;12 mfd. 20 v.,6d.; 25 mfd.25 v., 1/.. T.C.C. 4 or 8 mfd. 650 v., 4/-; 15 mill.50 or 100 v., 1/-; 50 mfd. 12 v., 1/,Paper Condensers. W.E., 250v. working 4 mfd., 2/-,2 mfd. 1/-, 1 mfd. fid. ; 350 v. working 4 mfd. 2/6.2 mfd. 1/6, Dubilier 500 v. working 4 mfd. 4/-;800 v. 4 mfd. 6/-; 2 mfd. 750 v. 3/-.Wego 450 v. working 1 mfd, 1/-, 2 ntfd. 1/9, 4 mfd.3/- ; 700 v. working 2 mfd. 2/-, 4 mfd. 3/6 ; 1,650 v.working 1 mfd. 3/6, 2 mfd. 5/S.TRANSFORMERS, latest type Telsen R.G.4

(list, 12/6), 2/9. Listen Hypernik Q.P.P.(list, 12/6), 3/8.E LIMINATOR KITS for A.C. mains. 120. v.

20 ma. or 150 v. 25 m.a., 10/-, tappedS.G. dot. and output. Complete Kit with long -lifevalve rectifier (replacement cost only 2/-).I ISSEN ALL -ELECTRIC A.C.4, S. Grid. Det.,

Pen. and Rectifier, M.C. Speaker. (List,£0.9.0.). Our price, 65/-.p.E.c. AC/DC ALL MAINS THREE. Ourga price, 75/-.Potentiometers by well-known makers. All valuesup to 1 meg., 2/- ; with switch, 2/8.



OUTHER RADIO'S WIRELESS BARGAINS.r.3 ALL GOODS GUARANTEED AND SENTPOST PAID.C PEAKERS.-Celestion Soundex Permanent Magnet,

10/-; Telsen Permanent Magnet with ten -ratiotransformer, 12/6; Blue Spot 99P.M. ExtensionSpeaker, 20/-; 45P.M. Extension Speaker, 17/6;Telsen Loud Speaker Unit, 2/6; all new and boxed.

RECEIVERS.-G.E.C. A.C. D.C. Mains Three -valvesets. Complete with 3 Osram Valves, in ex-

quisite Bakelite cabinet with Osram M.C. Speaker.Ready to plug in to any mains. Fully guaranteed.New, in sealed cartons, £3/5 (list £,7/15).

G.E.C. Colpact 3 -valve Battery Sets complete with3 Osram valves, moving coil P.M, Speaker in

attractive Bakelite, cabinet, makers 1936 series inoriginal sealed carton, 50/- (List 15/10/0).

MULLARD M.B.3 three -valve battery sets. Com-plete with batteries, accumulator, M.C.

Speaker. Three Mallard Pentode valves in beautifulwalnut cabinet. Brand new, in sealed cartons, 14/10(List 18/8).

TELSEN A.C. D.C. MULTIMETERS (latest 1031,type). -5 -range for every conceivable test for


W349, midget size, 4/-; type W478 (twin), 9/ -pair; type W477 (triple), 16/-; type W476 (triplesuperhet selector and oscillator), 16/- set. All GangedCoils are Mounted on Base with switch. I.F. Trans-former Coils W482, 5/-; Telsen Dnal Range Coil withvariable series condenser W76, 4/-; Varley SquarePeak Coils BP5, 2/-.

ELIMINATORS.-Regentone (1936) Type. W5awith trickle charger, 37/6; Type WIa (less

trickle charger), 32/6.HOUSE TELEPHONES. A SPECIAL BARGAIN.

BRAND NEW ONE -HAND TELEPHONES.Complete on stand, with or without Automatic Dials.Cost £4 each to manufacture, 10/- each.

MICROPHONES.-Aee (P.O.) Microphones, com-plete with transformer, perfect with any type

of receiver, 4/6.TEU-OHM RESISTANCES. -1 Watt. Wire ends

colour coded and marked ; 36 assorted capacitiesof, card, 6/-.

AMERICAN VALVES.-A full range of valves forall American sets at 7/- each. Brand new,

guaranteed.SOUTHERN RADIO BRANCHES. -271/275, High

Road, Willesden Green, N.W.10 ; 46, Lisle Street,W.C.2. All mall orders to 323, Euston Rd., N.W.1.

SOUTHERN RADIO, 323,. Huston Rd., London,NAVA (near Warren Street Tube). 'Phone:

Museum 6324.

A LCO ELIMINATORS AND CHARGERS. 4 H.T.taps. 120v/150v. 20/30 m.a., 18s., with

charger, 25s. Charger alone, 7s. 6d. 1 amp., lls.Year's guarantee. Details free.-P. & D. Radio,1, Goodinge Road, N.7.

BANKRUPTBargains. List free. G.E.C. battery

B Compact 3v. 42/6d. Alba S.G. 3v. 65/,American 12v. AC/DC superhets 8 -watts output.,all -wave, 14gns. Ecko 15gns., car radios 6v. or 12v.£7.10.0. Many others.-Butlin, 6, Stanford Avenue,Brighton.


21/- B.T.C. SHORT-WAVE GUINEA KIT.Reviewed July 4th issue. Latest design

for CONVERTElt - ADAPTOR ONE - VALVElt,13/52,m. Mains or Battery. No wiring. No soldering.Excellent reception reports. Descriptive Leaflet,11d. stamp. Order your Guinea Kit to -day.

BENNETT TELEVISION CO., REConis.L.

CLARION VALVES.-All brand new, battery types2 -volt, H.2, H.L.2, L.P.2, 1/9; super power

P2, 2/6; screens and L.F. pentodes, 3/9; A.C. mains4 -volt, 1-amp. general purpose, 3/3 ; power, 4/-;screens and L.F. pentodes, 4/6; full wave rectifiers,3/6; postage paid, cash with order, or C.O.D. over10/ -.-Clarion Valves, Dept. 2, 885, Tyburn Road,Erdington, Birmingham.

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August 8th, 1936 PRACTICAL AND AMATEUR WIRELESS

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VOLTAGE and CURRENT TESTSPA551

; Vol, 8. No. 204,August 15th, 1930.

By FRANK BOYCE

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ii PRACTICAL AND AMATEUR WIRELESS August 15th, 1936

Read This ThrillingTrue Story . . .

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RADIOLYMPIA-AUG. 26th SEPT. 5th-OUR STAND, No. 10

Technical Staff:W. J. Delaney, H. J. Barton Chap*, Wh.Sch.,

B.Sc., Frank Preston.

ROUND the WORLDVK6ME Australia

AFAVOURITE amongst short-wavelisteners, this Australian station is

being re -designed and rebuilt. A newtransmitter is to be installed at Perth, andis now undergoing tests at Sydney. Thissink with the Dominions forms a very goodreceiver test for the simple short-wavereceiver, and, no doubt, the new stationwill h even more reliable than the oldone.

America LeadsTHE latest returns from the International

Broadcasting Union show thatAmerica still leads the way so far as thenumber of listeners is concerned. There are,of course, no official records from theU.S.A. owing to the fact that no licences areissued, but the official estimate gives thenumber as 25,632,000 receiving sets. Nextto this total comes Great Britain with atotal of 7,695,452 licences, followed closelyby Germany with 7,599,252. The figuresfor France are 2,929,000, after which comesJapan, with 2,474,413.

Irish Broadcast RecordsAN announcement has been made that

the broadcasting authorities will infuture make sound records of importantevents in Ireland, but that unlike standardtypes of record, these special recordingswill play from the centre ,outwards. Theywill be made only of notable happenings inthe country and will be stored in a specialsound library at Radio Headquarters.

Automatic TuningTHERE have been one or two suggestions

for the automatic selection of a wire-less programme, from the separate time -selector to the automatic -tuning indicator,but from California comes a new suggestion.The device is claimed to be capable ofselecting as many as fourteen stations atfive-minute intervals so that any numberof separate items may be picked up auto-matically during the evening. As so farexplained, the device consists of a roll oftape which may be " punched " by thelistener, the punch marks coinciding withthe times and stations which are required.This roll is then inserted into the receiverand passes through a selector which switchesthe set on or off and tunes to the pre-selected stations.

VOL, VIII. No. 204. August 15th, 1936.4C61111131000.

549

Ground \Floor )

of WIRELESSLiverpool Police RadioFURTHER details have now been re-

ceived concerning the police cycleradio mentioned in our issue dated August1st. Our informant states that the 1924Armstrong super -regenerative circuit isemployed so that the noisy backgroundwhich is heard when no signal is receivedwill enable the policeman to know that theset is still working. This device obviatesthe use of expensive relays and enables the

' NEXT WEEK!i

i

1 ADVANCE OLYMPIA is

SHOW REPORTand

1

IMPORTANTI ANNOUNCEMENT I

concerning our

1 SPECIAL SHOWi NUMBERS I

officer to be released from the task ofswitching on and off and remaining other-wise alert for signals. The carrier fromH.Q. biases the first valve sufficiently tocut out the noises, and this gives the officerthe necessary warning to enable him torecord the message.

Netherlands Indies BroadcastsTHE NIROM started broadcasting

officially in the Netherlands Indies onMarch 31st, 1934, and now have twenty-twostations. Sixteen of them receive theirprogrammes over telephone lines from theBatavian key station, and the remainingsix broadcast local native programmes.The wavelengths used are all below 200metres owing to unfavourable atmosphericconditions, and the power of the mainTandjong station is 10 kW.

Vatican's New QSL CardTHE card sent out by the Vatican to

acknowledge reports of reception hasbeen re -designed, and the new card showstwo different views of the aerial system and.the transmitting gear of the station.

Athlone's Increased PowerTT is hoped that the power of the Athlone1 transmitter will be increased from 60 to100 kW by the end of September. This is,of course, the maximum power allowed byinternational agreement, and will enable thestation to cover a much larger area.

A DemonstrometerAMARCONI recording instrument was

recently described in these pages, anda similar device has also been used recentlyin America. In the case of the Americanapparatus a thermometer -like chart wassuspended in view of everyone, and a micro-phone in a parabolic collector picked upsounds from every part of the auditorium.The sounds were passed through an ampli-fier and caused a rise or fall in the "liquid"in the thermometer, and at the same timemade a permanent record in the form of thestandard graph.

Radiated PowerFROM America again comes news of an

epoch-making invention, this time thewireless transmission of power. Theinvention is attributed to Nikola Testa.the well-known inventor, but the fulldetails of the invention are as yet unknown.One report of the invention states that thetime is now not far distant when cars, trainsand similar machinery will be able tooperate by means of power picked up onmicroscopic aerials, micro waves beingemployed, and the received power beingample for such purposes.

Wails "" WJANS," for those who are anxious,

VV is almost an Irish equivalent of" ain folk." And when oul' besom manMat Mulcaghey from County Tyrone comesto the microphone again on August 24thhe will tell his crony, Sam Sweedlepipe,all about " Mulcaghey's Wans." However,listeners are not likely to take Mat asseriously as Sam Sweedlepipe does . . .

but that is anticipating the programme.

._.550 PRACTICAL AND. AMATEUR WIRELESS _ August 15th, 1936

THE PICK of the PROGRAMMESBaseball in Lancashire

ONEof the most surprising develop-

ments in the world of sport this yearhas been the growth of baseball clubs inthis country, and nowhere has this beenmore marked than in the North. Baseballhas already received notice in the Northernprogramme, but on August 15th listenerswill hear the first Northern runningcommentary on a baseball match.The match will be between RochdaleGreys and Oldham Greyhounds atWillbutts Lane, Rochdale, and thecommentator will be E. LandlessTurner, Secretary of the ManchesterCounty Baseball Association.

" The Bunch of Roses "DIANA MORGAN and Michael

Sayer, who collaborated in themusical play " Bertie " last year,have written another musical showwith a strong note of burlesqueentitled " The Bunch of Roses."The play, which will be produced byCyril Wood in the National andWestern programmes on August12th and repeated in the Nationalprogramme on August 14th, is set inthe West Country, and " The Bunchof Roses " is the name of an innwhere a mixed collection of peoplegather, including commercial travel-lers, an inn -keeper, highway robbers,Surrealists, a detective and a youngwaitress. Two of the songs, " Roses "and " Midnight Magic," were recent-ly broadcast in " Music Into Play."

A Welsh Religious ServiceELFED, the only surviving ex-

Archdruid, will preach at areligious service in Welsh to bebroadcast from Tabernacle Con-gregational Church, Fishguard, onthe Sunday following the NationalEisteddfod. The Rev. H. Elvet ofignattmLewis, who is the minister of King'sCross Church, is well known as apreacher, a hymn -writer, and a poetof no mean ability.


Li).=4141.41.44141-1SH1.101.11.4414.4,000.11.416WOOi,i11-414411.11.

of gramophone records to the boil and then-all this does not sound very palatable,but those who have already had servings ofScotch Broth will know that they are good.

SANDY POWELL AND PYE

Pye's latest release, battery portable type T.61, is here seenproviding Sandy Powell with a little light entertainment in hisdressing room. He is dressed for the r6le of coffee shop proprietor.

Spinnle Climbs His Monkey PuzzleDDEOPLE who are curious about theirr genealogy and have searched therecords do not always return from theirstudy with aglow of pride. That intrepidold gentleman, A. Spinnle Shanks, whobroadcasts his experiences for the benefitof Scottish listeners on August 14th, isunlikely to be more fortunate than the restof us. Indeed, there is a suggestion thathis family tree is of the genus MonkeyPuzzle. Both ascent and descent of thespecies are likely to be amusing to therest of us.

Later in the evening an excerpt fromHarry Kemp's Summer Show will bebroadcast from the Barrfields Pavilion,Largs. Taking part are Dave Bruce, ElsiePrince, Percy Manchester, Jack E. Ray-mond, Ann Doel, The Saxon Girls andHarry Carmichael and his Band.

Hare BrothHOWARD THE HARE, beloved by

listeners to the Aberdeen Children'sHour, will offer another plate of ScotchBroth on August 15th. As may be expectedwhen a hare turns cook, the ingredientsare bound to be unusual. What Howardapparently does is to bring a collection

MINE THIS .1PROBLEM No. 204.

Cousens bought an eliminator for supplyingILL to his S.G.3 receiver, but found that it wasnot provided with an S.G. screen tapping.What method should be adopted for supplyingthe screen ? Three books will be awarded forthe first three correct solutions opened.Address your letters to the Editor, PRACTICALAND AMATEUR WIRELESS, George Newnes,Ltd., 8-11, Southampton Street, Strand,London, W.C.2. Envelopes should be markedProblem No. 204 in the left-hand corner,and should be posted to reach this office

i not later than the first post Monday, August17th, 1936.

I Os Os 41 Oa 8.0. 4. Os 4s v..: 4 Oa

Solution to Problem No. 203.The grid -bias voltage applied to the power pentode

would be approximately 9 volts, and as this would beexcessive for the new economy type pentode signalswould be weakened and quality of reproduction woulddeteriorate.

The following three readers successfully solvedProblem No. 202, and books are accordingly beingforwarded to them : John Surtees, 31, Spencer Street,Heaton, Newcastle -on -Tyne 6 : H. Pegg, 146, LawfordRoad, Rugby : P. G. Skane, Beverley, RoystonAvenue, Prittlewell, Essex.

" Crowded Moments "THE fourth of the series of impressions,

entitled " Crowded Moments," willbe broadcast from the Bridgwater BandFestival at Blake Gardens, Bridgwater,on August 15th (West Regional Programme).After hearing the Massed Bands play,listeners will hear Hedley Goodall introduce

the Mayor of Bridgwater. This willbe followed by a summary of theresults by the adjudicator who willpresent the conductor of the winningband. The conductor will thenconduct his band in the test piece.

" Wings Over Westralia "WINGS Over Westralia " is the

dramatised story of the epicflight of two young German aviatorsin May, 1932, from Cologne to theNorth Coast of Australia. They gotlost over the Timor Sea and landedsome hundreds of miles away fromtheir objective, which was Darwin.They were lost in the bush and verynearly died of starvation, but behavedwith considerable fortitude. Theaction of the play consists largely ofthe search for them.

The author, Gordon Ireland, is anAustralian, and Lance Sieveking has,in order to get the correct accents,cast the play entirely with authenticAustralians with the exception of thetwo Germans themselves, who will beas nearly German as can be managed,the narrator, who will be English, anaboriginal and two Spanish Missionfathers, who will be cast in the usualway. It is hoped that the generaldramatic effect of the whole storywill be much enhanced by the fresh-ness of the unfamiliar cadences andaccents of the cast. It has been avery difficult matter to get hold ofthe requisite number of Australians,because most of those who have livedhere any time have lost their Aus-tralian accent and so are rendered in-eligible. The programme will be heardfrom the National on August 12th.

Concert PartyFROM the Jephson Gardens Pavilion at

Leamington Spa a concert party enter-tainment by the Kit-Kat-Kits, presentedby Bert Brownbill, will be relayed from theMidland on August 21st. This Companyof seven bright young people was foundedin 1931, and in that year began at Newquay,in Cornwall, a series of seaside engagementswhich has extended to many of the mostnoted resorts. Mr. Brownbill, who iscomedian as well as producer, was for a longtime with Julian Wylie productions. Thesoprano, Agnes Hirst, was at the Gaiety andAdelphi in London ; Lena and Follie aredancers and duettists Olaf Kossen is thelight comedian and dancer ; Leslie Childsis the entertainer, mid Jack Lawton thepianist.

Violin and Pianoforte Recital

PAULBEARD, who is to be the violinist

for this recital on August 22, hasrecently been appointed to succeed ArthurCatterall as leader of the B.B.C. Orchestra.His grandfather was a Birmingham singer,his father a violinist and viola player.For several years he was leader of theCity of Birmingham Orchestra. The pianistwill be Margaret Ablethorpe, who is MidlandRegional's accompanist.


Voltage and Current TestsSome Notes on the Use of Meters for Fault-finding and

Receiver Testing and Checking. By FRANK PRESTON

ALTHOUGH it is possible to locate thesource of many forms of troublewithout the use of instruments, the

matter is generally simplified when a goodmulti -range meter is available. !And sincesuch an instrument, of quite good quality, can now be, bought cheaply enough it isworth while for every constructor and

Fig. 1.-The filament voltage of each valve shouldbe checked by connecting the voltmeter as shown

here when the set is switched on.

experimenter to invest the few shillingsrequired. Do not buy an unbranded meter-that might be worse than useless-although it is not necessary for normaltests to spend more than about two pounds,for which price a moving -coil unit withup to ten ranges can be obtained. Itis, of course, possible to buy a meter forlittle more than half this price, but itcould not be relied upon for any other thanvery rough checks. On the other hand,you can spend up to ten pounds for ahigh-grade unit with a guarantee of accuracyof about one per cent. ; that price wouldnot be justified, however, in the case of theusual home constructor.

High -resistance VoltmeterSee that the meter to be bought has a

reasonably high resistance, because other-wise it cannot be accurate for many of themeasurements which it will be requiredto make ; a figure of about 500 ohms pervolt for the voltage scales is reasonable.This means that the meter will not passmore than 2 mA when the voltage of, say,a high-tension battery is being taken.A cheap, low -resistance meter might takeas much as 20 mA, with the result that thevoltage registered might be appreciablyess than that of the battery. Additionally,the meter would soon run down the batteryif used frequently. The milliampereportion should have a low resistance-andall reputable makes of moving -coil metercan be relied on in this respect.

Under " Load"But even the best meter obtainable is

useless if the owner does not know how touse it. Our correspondence shows thatthere are many readers who have boughta meter, or even who have made a multi-purpose one from details published in thesepages, who have no idea how it should beemployed for testing and checking. Letus deal with the principal readings whichhave to be taken when a set is being tested.

First of all we want to know the voltages ofthe high- and low-tension supplies. It seemsquite obvious that all that has to be doneis to connect the two prods or leads of themeter to the positive and negative terminalsrespectively. If this were done withoutthe set being switched on the readingswould probably be entirely false : an H.T.

Fig. 2.-Check anode voltages by connecting themeter as shown here.

battery which was badly in need of replace-ment might show almost full voltage ; arun-down accumulator might register 2

N.T.. r-

Fig. 3.-Besides testing for anode voltage, as shownin Fig. 2, it is often wise to test between earth andthe points marked A, B and C in this skeleton

circuit.

volts ; and the voltage from a 150 -volteliminator might appear to be 250 or more.

tow

Fig. 4.-G.B. voltagecould not be read Zaccurately by joininga meter between pointsX and Y, althougha fairly accurate reading would be obtainedby connecting it to the points Y and Z. This

assumes G.L. to be in good condition.

H r-

The reason is that the voltage varies accord-ing to the "load," and it is only underworking conditions that a useful readingcan be ensured.

L.T. and H.T. VoltagesAfter measuring the voltage at the input

terminals to the set, apply the prods to -thefilament terminals of each valve holder inturn, as shown in Fig. 1. If the voltage atany pair of terminals is less than that atthe mput terminals either the switch isfaulty or there is a bad connection in oneof the leads. Next, after suitably adjustingthe meter, measure the voltage betweenthe anode terminal of each valve holderand earth, as in Fig. 2, In any case thereading will be rather less than the actualvoltage, due to the increased load providedby the meter-which is in parallel withthe valve-but the difference should notbe great except in the case of a detectorvalve passing a very small current andhaving a high value of resistance in itsanode circuit. If any valve does notappear to he receiving its correct voltage,make further tests at the points marked A,B and C in Fig. 3. (Two different circuitsare given, one applying to an H.F. valve,and the other to a detector or L.F.) There

should be a progressive increase inHT* voltage when the positive prod is moved

in turn to these points, although the differ-ence !might be negligible as between thetwo iends of the H.F. choke or primarywinding of an H.F. transformer)

Should it be found that there is no indi-cation of voltage between earth and, say,point A, although a reading is obtained bymoving to B it will he evident that thecomponent situated between these twopoints is defective. In the same way, ifthe voltage difference is very pronouncedit might indicate that the component has ahigher resistance than it should have.

G.B. TestsIt is not always easy to measure the grid -

bias voltage which is being applied to thevalve, for the reason shown in Fig. 4.If the meter were connected between thegrid and filament of the valve it might beimpossible to obtain a reading, whilst- if onewere obtained it would be considerablylower than it should be. This is due to theresistance of the transformer or grid leakwhich would be in series with the C.B.supply, and also due to the fact that themeter partly short-circuits the grid -filament


SET TOvocrs

Acr-

Fig 5.-A fair, though not quite accurate, kit olG.B. voltage is possible as shown here,

552 PRACTICAL' AND AMATEUR WIRELESS August 15th,_ 1936(Continued from previous page)

circuit of the valve. One method ofmeasurement is as shown in Fig. _4, -wherethe meter is connected between earth andthe G.B. negative lead to the transformer,grid leak or coil. The reading obtainedeven in these conditions might not beperfectly accurate when a variable G.B.voltage is being applied to an H.F. valvethrough a potentiometer, but if the voltage

- +-spitr+

Fig. 6.-Total anode current should be checked byconnecting at A and this compared with the sum ofthe readings at the three points marked. A leakyby-pass condenser can be checked by inserting themeter at Z and the current taken by an S.G.

potentiometer by inserting the meter at Y.

varies smoothly as the potentiometer isoperated it will be sufficient evidence thatthe circuit is operating correctly.

In the case of a mains receiver thedifficulty is still greater, because the onlyreally simple method of measurement is byconnecting the meter between the ends ofthe bias resistance, as shown in Fig. 5. Whenthis is done the meter is in parallel with theresistance, so that the effective value of thelatter is reduced. Nevertheless,. providedthat the voltage is rather lower than thatrequired, the test will be sufficient for most

purposes.. The absence of a voltage readingwould show that the resistance was eithershort-circuited by a defective by-passcondenser or open -circuited due to thecomponent being faulty.

Anode CurrentThe anode current passed by all the

valves together, and also by each in-dividually, -should be checked and a com-parison made. That is, if the meter reads20 mA when connected as shown at A inFig. 6, and only 3, 1, and 9 mA when in-serted at the points marked X, it will beclear that there is a partial short-circuitsomewhere. Before concluding that somecomponent or connection is faulty, however,make quite sure that a screening -gridpotentiometer is not used, or if it is thatthis does not account for the extra 7 mA, byinserting the meter at the point marked Yin Fig. 6. In making this test, see that thevariable -mu volume control (where fitted)is set to the same point during the takingof all measurements. Incidentally, the bestmethod of measuring the current to eachvalve is by using a split -anode adapter,as shown in Fig. 7, and by connecting a.1-mfd. fixed condenser in parallel withthe meter, as shown ; this is to preventself -oscillation which might otherwise arisedue to the resistance of the meter.

When any component such as a by-passcondenser is suspected of being faultyso that it passes current, an easy check canbe made by inserting the milliammeter atthe point marked Z in Fig. 6. Thereshould be no reading in this case if thereis the condenser must be at fault, unlessthere is a partial short-circuit between twoleads joined to it.

CautionA warning should be given that the

receiver should be switched off every timethe meter is to be changed from one pointto another. Additionally,it should be made

quite certain that the meter is properlyattached, and that there are no bare leadsor loose wires which might come adrift.Lack of caution in this respect mightresult in the battery or the valves beingpermanently damaged. Still more careshould be taken where a mains receiver isconcerned, because a short-circuit might" blow " a main fuse, and accidentallytouching an H.T. point might result in a

Fig. 7.-This shows how a split -anode adaptercan be used to measure the anode current in

any valve.

severe shock. Remember that it is notalways sufficient to switch off the set,because fixed condensers might storequite enough current to give a nasty" kick " if the terminals are touched. Tobe on the safe side it is well to short-circuit each large -capacity condenser afterswitching off and before connecting themeter. This can be done by holding asmall screwdriver by the wooden handleand simultaneously touching the twoterminals with the bare blade ; no need tobe alarmed if a fat spark is seen when theterminals are bridged.

AUTUMN PROMENADE CONCERTSIT is announced by the B.B.C. that new

English works will be performed forthe first time during the present season

of Promenade concerts, which began atQueen's Hall on Saturday, August 8th.

-On August 13th, there will be a first con-cert performance of " Salute to GustavHoist," by John Greenwood, who i s wellknown as the composer of the music for thefilms " Man of Aran " and " The ConstantNymph." Then on August 29th comes afirst performance in its orchestral dress ofJohn Ireland's " Overture," originallywritten for Brass Band. The theme is amusical version of the word " Piccadilly,"suggested to the composer on hearing abus conductor calling out the word withvarying intensity for the information ofhis passengers.

" Three Scottish Dances"Ian Whyte, whose " Three Scottish

Dances," conducted by the composer,will receive their first concert performanceon August 31st, is the B.B.C. Director ofMusic in the Scottish Region. ProfessorGranville Bantock's new Comedy Overture" The Frogs" will be played for the firsttime on September 9th, the compoierconducting. Apart from the fact that thisOverture contains a brief allusion to Aristo-phanes (The Croaking Chorus), it mightserve, in the words of the composer, as an

introduction to any Greek play. It carriesho special programme, and is a completemusical work in itself.

Five foreign composers will be representedby new works to be performed for the firsttime in a concert hall in England duringthe " Proms " season. One is a Russian(Vladimir Vogel) ; one a Hungarian (Ernstvon Dohnanyi) ; one a Finn (Jan Sibelius) ;one a Frenchman (Jacques Ibert) ; andone a Belgian (Armand Marsick).

Vogel's Ritmica Ostinata," to be playedon August 18th, was broadcast from aB.B.C. studio under Dr. Boult's directionin June of this year ; but the " Proms "will see its first concert performance inEngland. It is one of three studies fororchestra, the other two " Ritmica Funebre"and " Ritmica Scherzosa " having beenperformed at the Oxford -London Festivalof the International Society for Contem-porary Music, in 1931. It is based on amarching song, and was originally composedfor a Brass Band.

The " Minutes Symphoniques " by Doh-nanyi (September 4), whose music is familiarin this country, were also broadcast lastseason, but have never previously beengiven in a concert hall in England. Norhas " The Ferryman's Bride " by Sibelius(September 10), although this is a com-paratively early work, being his Opus 33.It is described as a ," Ballad " for Mezzo-

soprano and Orchestra, and is based on aFinnish legend.

" Concertino "Jacques Ibert, composer of the " Con-

certino " for Saxophone and Orchestra(September 12th), is a contemporary ofMilhaud and Honegger, and one of thebest-known French composers of theirgeneration. Like so many composers hewas once a naval officer, but in 1919 he wonthe Prix de Rome for composition, andsince then has written operas, ballets,concertos for 'cello and flute and muchorchestral and chamber music. While`inRome at the Villa Medicis he 'composedmusic to Oscar Wilde's " Ballad of ReadingGaol." The Saxophone Concertino was first'performed at the International Society forContemporary Music in Barcelona last April.

Armand Marsick whose " TableauxGrecs " will be performed on September29th, is one of the leading figures in con-temporary Belgian music, conductor of theLiege Symphony Orchestra, and Professorof Harmony at the Liege Conservatoire.Marsick was formerly Director of theConservatoires of Athens and Bilbao, andis looked upon as the. Ambassador ofBelgian music abroad. His compositionsinclude " Symphonic Poem, La Source,"and three operas-" L'Anneau Nuptial,"" Lara," and " La Jane."

August 15th, 1936 PP.ACTICAL AND AMATEUR WIRELESS 553


SUBMI

YOURIDEA

READERSCombined U. -S. -W. Valve -holder

and Filament Choke'I LAMENT chokes improve the working

of many ultra -short-wave circuits andare essential for some of those of the" long line " or lecher wire type. To beeffective the chokes must be as close to thevalve as possible.

An efficient combination of U. -S. -W.valve -holder and filament chokes can bemade from a valve-base-one with parallelsides and of good material is required.

The pins are extracted and four valvesockets fitted in their place. The grid andplate sockets have a small strip of brassclamped or (preferably) soldered underthem for the attachment of lecher wires or

- VALVE

SAW-curs

FILAMECHOKE

WINDINGS

CORK. VALVEBASE.

An idea for a combined U. -S. -W.and filament choke.

c,)ils. Two deep saw -cuts are made atright angles to each other and between thesockets to interrupt the leakage path andreduce dielectric hysteresis.

The chokes themselves are wound in" bilitar " manner-i.e. the two wires arewound together, side by side-about fifteendouble turns are suitable for from 2,1i to10 metres. The top ends of the chokes aretaken through a small hole drilled in theside of the valve -base. and of coursesoldered to the filament sockets. Thisbolder may conveniently be mounted bybeing pressed on to a suitable cork screwedto the baseboard.

A further advantage of this arrangement,is that the vale is kept away from thebaseboard, and at- a level suitable for thedirect attachment of coils, etc.-R. H.McCrE (11.11111111i).

A Valve -testerI HAVE seen several valve -testers in

PRAt7IC.1il, AND AMATEUR WIRELESShilly, but none of them will detect high -resistance inter -electrode shorts. whichare serious in 11.F. valves. I think thistester overcomes that difficulty.

valve-hqlder

THAT DODGE OF YOURSEvery Reader of " PRACTICAL AND

AMATEUR WIRELESS" must haveoriginated some little dodge which wouldinterest other readers. Why not pass it onto us ? We pay fl -10-0 for the best wrinklesubmitted, and for every other item publishedon this page we will pay half -a -guinea. Turnthat idea of yours to account by sending itin to us addressed to the Editor, " PRAC-TICAL AND AMATEUR WIRELESS,"George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, W.C.2. Put your name andaddress on every item. Please note that everynotion sent in must be original. Markenvelopes " Radio Wrinkles." Do NOTenclose Queries with your Wrinkle.

iS

Should the note of the oscillator circuitnot be heard when the switches are asshown, the filament is broken. Should itnot be heard when the switches are at P,the tester is not functioning.-R. J. WOOD(Leigh -on -Sea).

An " Economy "SwitchTHIS switch will be

of interest tomany constructorsusing a high -voltageH.T. supply obtainedfrom a directly -heated rectifier, andwho would like toincorporate a thermaldelay switch in theirset but have not sufficient current tooperate it. The fundamental idea in thisswitch is that the S.P.C.O. switch AB, CDcuts out the heater winding on the thermalswitch as soon as H.T. current passesthrough the operating coil, at the same timeshorting out the H.T. contacts of theswitch and allowing the H.T. current toflow r'eirect from the C.T. on the rectifierwinding, via the operating coil, whichkeeps the contacts CD closed whilst thecurrent is flowing through it.

When the set is switched off a weakspring pulls the armature back, joiningcontacts AB and opening CD. Points tonote in the construction of the switch are :

10 EITHER FILAMENTTERMINAL ON RECE-RHOLDER.

SOLDERED

TO THERMALSWITCH HEATER,

SPRINGY BRASSCONTACTS

Ih min,V;.

10 C.T.ON TRANST

PAXOLINSTRIP

TO HT OUTPUT FROMTHERMAL SWITCH.

1, The coilsmust be woundto include op-posite polarityin the polepieces ; 2, Themoving contactsB and D mustnot stick in thefixed contactsA and C ; 3,The strength ofthe electromag-net must besufficient toovercomethe spring,which mustbe able topull back

THE

HALF -GUINEA

PAGE

Mr. R. J. Wood's sugges-tion for a valve -tester.

the armature. An old electric bell will doexcellently but the coils must be rewoundwith about 3,000 turns on each ; any gaugewire may be used, but the finer the wire isthe less current it will carry and the greaterits resistance. Also, a new arm must be fixedto the armature to carry the moving contacts,the leads from which should be attached tothe arm by a few turns ofcotton at various places.-A. M. Wnr..nucc.( Wall asey).1

THERMAL DELAYSWITCH.

A

COILS WOUND INOPPOSITE DIRECTIONS

This economy switch isuseful when the L.T. wind-ing on the transformer is,

fully loaded.


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/ 97/4 P/. 4 997. 11. 49/ /49"I"

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V.Ro 2.21A variable -mu screened H.F..Piht-digle for use in batteryreceivers.The valve is speciaLlytonstruct4 for use under conditionswhere freedom ittlam microphorlic noise is required.The anode -grid -rapacity is only 0.004 Weld.RAT( Ntf;77'

4

Filam6neNts-- - - 2.0 Filcm4t1t Current -Max. Anode_ Volts 150 Max. Sateen Volts

Mutual Conductance 1 4**at Ea120v. Es60v. EgO

v.

- 0.1- 150

The bulb isrmetallised aAd fitted with a 7-pin..,standardbase.

PEN E

PEN. 231A high slope output pentode for use..ifebattery receiverswith a self -biased circuit.RATINGFilament Volts - - .0 Filament Current - 0.3Max. Anode Volts - er' 150 Max. Screen Volts 150

Mutuctr Conductance - 5.3**at Ea100 Es100 EgO.,

TYPICKL. OPERATING CONDITIONS..eetnode Volts - - - - 120 Screen Volts 7 -

Grid Bias - - - - 2.5 Anode CurrentOptimum Load - - 19,000

The valve is fitted with a standard 5 -pin base.

D 'SWAN

- 120- 5.0

Full details these valves and others in the MAZDA range can be obtained on application to the Technical Service Dept.Mazda Radio Valves are manufactured in Great Britain for The British Thomson -Houston Co. Ltd., London and Rugby, and distributed byTHE EDISON SWAN ELECTRIC CO. LTD., 15S CHARING CROSS ROAD, I.ONDON, W.C.2 R.M.292

........

/// Zeor.x7/27/17/17 .e././ AYZ /47 .47./.1 Ar///././177 Z., /Al/ Alt6W1/1/7.117.W/ La/ /44/ /41/7/Y47 /4/174414/ 400744Z/ol447.7244,74401

23 4. 33 3 . .0.7 / / ..,7 : /e/ .e, #.07/.//e/

0 /

0

This is one of the famous Newnes Home

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Is Our Radio Feeble ?ACORRESPONDENT who wishes

to create a modern Tower ofBabel says that the voice of Britainshould be heard all over Europe.He thinks that the low power of ourstations is ridiculous when comparedwith that of Russia, Germany, andFrance. The selectivity problem issufficiently acute in England, he says,!for us to give the foreigners a taste oftheir own medicine. This individualmust live in a detached house sur-rounded by a moat. Like most otherhuman beings, I have neighbours,some of whom like to operate setswith at least 5 watts output, so that Iseldom, have to use my own set.Most people with a good set are veryproud of it, and like to let the neigh-bours hear how loud it is. If theB.B.C. increased the power of thestations this correspondent would bethe first to complain of swamping,

Radioads.

and he would probably write a" snorter " to the B.B.C. asking themto buy him a new set.

Radioadsj NOTICE that a radio feature in a

1 j daily paper is headed " Daily'Double." It deals with a couple ofselected proarammes which it recom-mends to the attention of its readers.Now I think the racing correspon-dents, should retaliate by heading,their dead cert..nap " Short .Waves'from the Course," or " Variety Pro --gramme at 'Epsom."

The boxing correspondent mightIhead his page Round the Dial," andthe tennis correspondent " All forLove." The Rugger writer. wouldWrite under a feature heading en-titled " I've Got a Hunch:"

"Ber-lud and the B.B.C.Pr OD SLAUGHTER likes a spot of

melodrama when he treads thestage. Some few months ago, you

avelengthBy thermion

will remember, he broadcast the" Crimes of Burke and Hare." Atthat time many nice people thoughtit was lacking in good taste to dealwith the famous case of body snatch-ing. Now it appears that when TodSlaughter wished to give " EastLynne " the Empire producer de-manded " horror," and suggested the" Crimes of Burke and Hare." Ap-parently there is still a public for theold style of melodrama in which thered blood flows, like " Maria Marten,or the Murder in the Red Barn."

S eakers and SpeakersAYING a social call, recently, I

was invited into a tastefullyfurnished lounge containing a largeradiogram oozing decibels and phons._There were six or seven other guestspresent and there were three separateand lively conversations being carriedon at the same time. The speakershad to shout in order to make theirvoices heard. No one paid theslightest attention to the "radiogram.This ordeal lasted during the fullperiod of my visit-some thirtyminutes. I wanted to ask my hostthe reason, but I could not summonup the breath necessary for thestentorian bellow required to makemyself heard.

Radio in ShanghaiHAVE received the following most

I interesting letter from 'Mr. G. A.Kemp, of Shanghai :-

" I have often wanted to write toyou, and now, as I am having mysummer holidays, I am getting downto the task of writing you a longscreed. Firstly, allow me to praiseyou for your article which appearseach week under the title of OnYour Wavelength.' I have been aregular subscriber b PRACTICAL ANDAMATEUR WIRELESS for the last yearor so and am of the opinion that itis one of the best papers on wirelessthat can be bought here. Contrastingit with other magazines, I find thatit is vastly better than, for instance,the majority of the American maga-zines which nearly everyone here buyswho is interested in wireless. Your

paper costs me 40 cents a week, andthe American papers are I dollarper month. And are they worth it ?

" Coming to your article again, andnot having had the pleasure of writingto you before, I might say that Iwholly agree with you and what yousay about crooners. In China, wherestations broadcast records most of thetime, we get crooners of every sort. Howdo you like Hawaiian music ? Awful,isn't it ? I'll tell you a whole heapabout local broadcasting right now.

In Shanghai, about two years ago,there were ninety-eight broadcastingstations registered. About fifty of themoperated every day at the same time.There were no laws about overlappingeach other, nor about keeping to anyset frequency. You can imaginewhat it was like. Most of the Chinesestations did not have their signalsmodulated at all, and their great aimwas to get out the rowdiest signal

B.B.C. and Ber-lud.

they possibly could. Now it is better.There are only about thirty-sevenstations on daily between 2o6 and516 metres ; there are seven Euro-pean stations and the rest are Chinese.The strongest are only i kilowatters.You do not have to have such a thingas a licence here, although the Govern-ment tried to get people to registertheir receivers (and this was onlypartly successful), but stations are runon the American system of havingsponsored programmes. As I saidbefore, gramophone records are themainstay, but there are also relaysfrom the local dance -halls, fromchurches, and, very occasionally, fromabroad. It is supposed to be com-pulsory for every station to relay theNanking Government station between8.3o and 9.35 at night, but there wasa row about that. Many stationowners said that this was the mostimportant hour of the day for them,and if they complied with this order


no one would sponsor the hour andthey would go broke pretty quick.The foreign stations did as they weretold, with the exception of one whichcarried on in the same way as before,and said ' So what ! Nothing wasdone about it !

" If you' are a short-wave enthusiastyou may have heard some of thestations at Shanghai which are usedfor telephone work. There is a short-wave station at Nanking on approxi-mately 31.6 metres. He is usually onabout 12-14 hours G.M.T. Hong -Kong (ZCK) is on daily, brit the timesare somewhat bewildering. In G.M.T.they are as follows. Daily, 4.30-6.0o.Mon., Wed., and Friday, 9.00-12.00.Tues., Thur., Sat., Sunday, It .00 -

Speakers and speakers.

3.00. Also on Sundays, 2.30-6.00.Wavelength 34.29 metres. Address :Post Office, Box zoo, Hong -Kong.

" As regards sets and parts here, Iimpart the following. Receivers areabout 95 per cent. American. Thereare many Japanese as well as Chinesesets on the market. A Japanese 5 -valvesuperhet, all -mains, can be boughtnew for as little as 15 dollars, or atthe present rate of exchange about18 shillings. Hold that one ! Thenthere are parts. English parts areexpensive, but they are worth everycent of it. For instance, a Ferrantipush-pull transformer costs 41 dollars.I bought an ordinary Japanese L.F.transformer for 45 cents.

" It works 0,K., but I should be veryinterested to see this thing go througha test that our makes have to gothrough. Resistors can be got for id.Variable direct drive condensers for5d.. Soldering irons for i id., mainstransformers for Jos., 3o -amp. accu-mulators for 2S. 6d., and coils, can bemade for lid. Some of the stuff isnot to be laughed at, although itwould not be of any use in a short-wave set. Recently I went downPeking Road (noted for its rows ofsecond-hand shops) and came acrossa Polar .00025 mfd. condenser. Itwas absolutely new, and, knowingthat they cost 8 dollars here, I askedthe man how much he wanted for it.He said $2.50. I didn't wait long,but snaffled it up, knowing jolly wellit would be years before a Polar wassold at that price again. Either the

S.W. Receivers 4,

THE S.G. valve does not providea very high degree of ampli-

fication below too metres, hut theinclusion of an S.G. H.F. stage in ashort-wave receiver is, nevertheless,an advantage. It smoothes thereaction control considerably andalso improves the selectivity. In aset intended for short-wave receptiononly, it is, therefore, advisable touse a tuned aerial circuit followed byan S.G. H.F. valve coupled by asecond tuned circuit to the detectorvalve. When the set is to be usedfor all -wave reception, however, theuse of two tuned circuits complicatesthe switching and consequently in-troduces instability unless very greatcare is taken with the layout andwiring. The advantages of using atuned aerial circuit are thereforecounterbalanced by disadvantages.This does not mean that it is animpossibility to obtain optimumresults from a receiver using twotuned stages for covering the shortand broadcast bands, but experi-ments indicate that this type ofreceiver is difficult to design. Withan aperiodic aerial circuit in useinstability is not experienced and acertain amount of H.F. amplificationis still obtainable.

Speaker EnergisingMAIM -ENERGISED moving -coil

speakers generally provide betterresults than a permanent -magnet type.This is due to the fact that the fluxdensity in the gap is greater with themains type if the correct value of ener-gising current is used. The expensivepermanent -magnet models have a veryhigh density, of course, and comparefavourably with the mains -energisedtype, but their price is rather morethan most constructors care to expend.If D.C. mains are available a mainstype speaker can be cheaply energisedby connecting its field winding leadsacross the mains leads. Great caremust be taken to choose a componenthaving the correct field resistanceto suit the mains voltage, however.When this is between 220 and 25ovolts a field winding resistance ofbetween 4,50o and 6,500 ohms shouldbe chosen if the speaker is of themedium-priced 5 -to watt type. If aspeaker having a resistance of 2,50oohms is available, the winding may beconnected in series with a 2,500 ohmto watt resistance.

chap stole it from somewhere or etbought it at an auction (even neparts are sold for a mere song)."

Teacher PaysWHERE xvireless sets are install

in schools so that the scholarscan " listen -in " to school broadcastsit is often the teachers themselves whopay for the set and its upkeep.

An investigation just completed bythe Staffordshire County Associationof the National Union of Teachersshows that only 81 out of 490 schoolspossessed wireless sets, and that inonly five cases had the local educationauthority paid for the set.

" Teachers themselves," the -

vestigators report, " have been largely

" Personally. I have neighbours::

responsible for the expense attachedto the provision of a set either byusing funds accumulated from someschool activity, or by providing themoney themselves, or by loaning theset to the school. In a few cases someinterested person outside the imme-diate.school organisation has provideda set."

No Funds for RepairWITH regard to expenditure in-

volved in maintenance of thesets, or in the purchase of a licenceor of pamphlets, the local authoritygave assistance only to half the schoolswhere sets had been bought or lent.

A number of schools where setshad been installed by the teachers orthrough the efforts of scholars hadbeen forced to discontinue broadcasttalks, owing to lack of funds forrepair or the provision of pamphlets.

The threat of the broadcast lessonto the teacher is largely discounte-nanced.

" School broadcasts," the reportstates, " require the active co-opera-tion of the Class teacher and theycannot displace his class -room work."

Mr. I. Badger, of Stourbridge, waschairman of the Inquiry Committee,and Mr. H. H. Cartwright, of Dudley,who is on the N.U.T. executive,was one of the members. Mr. Cart-wright has taken an important partin the development of school broad-casts and is a member of the B.B.C.Central Council for School Broad-casting.

THE amateur and experimenter arealready becoming Olympia con-scious, and not many weeks now

remain before the doors will be opened andthe vast range of new season's goods will beon view. What will be the trend of designthis year ? What new lines shall we seedeveloped for the home -constructor ? Willtelevision components be available for thehome construction of television receivers ?

These are only a few of the many questionswhich constructors are now asking, and it istoo early to answer them all. The informa-tion which has come to hand so far showsseveral interesting developments, and nodoubt one of the most important is theperfection of the single -knob control.There have been many attempts in -the past


Some11111111111111111111111111111111111111111111111

Although Full Details Have

OLYMPIA SecretsRevealed 11111111111111111111111111111111111111111111111

Not Yet Been Released by all the Manufacturers, One or

Been Revealed, by Certain Firms, and Some Details are Given Here

where a singleknob is employedand the rotationof this knob turnsthe pointer withmaximum speed(which is very fastindeed), but assoon as the userarrives at approxi-mately the tuningpoint required, aslight backwardmovement is madeand the drive isthen through areduction gear,which is again -ex -

to reduce the number of controls, butgenerally the reduction simply consisted inthe elimination of one or two controls which,whilst not essential were nevertheless ofgreat value in obtaining maximum perform-ance, or two or more controls were gangedtogether and operated by concentric knobs.

In the Philips receivers will be seen thelatest iruSingle-knolasontrol, where only oneknob is employed, but that knob controlstuning, volume, tone, and selectivity. Theknob may aptly be referred to as a radiojoy -stick, for it consists of a small knurledbakelite knob working in a universal ball-

, joint movement, and through the medium9f bowden leads it actuates the variousseparate controls. The knob itself may berotated, whilst the entire assembly is movedin the ball-and-socket joint, -the rotation ofthe knob effecting the tuning, and thedirection in which the knob is moved con-trolling the remaining effects.

Two -speed TuningIn the Philips receivers, too, will be seen

a novel development of the two -speed drive,

tremely slow.After a few turnsthe gear againpicks up and move-ment may be car-ried out rapidly.

Eliminating theBatteryThe drawback of

the battery user,namely, the con-tinual replacementof the high-tensionbattery is nowclaimed to beremoved entirely,by the adoption ofthe vibratory con-verter or some

On the right is thelatest H.M.V. Auto -radiogram, employingthree loudspeakers.

Above - the controlpanel of the H.M. V.receiver shown below.On the left, a newPhilips receiver show-ing the new " Mono"

knob control.

Two Secrets Have

similar device, which is operated from theL.T. accumulator, and with very little extradrain on the supply will develop thenecessary high-tension voltage. Messrs.Ekco have perfected the device, and it willbe seen fitted to some of their batteryreceivers; how successfully we shall seelater.Good News for D.C. Users

The listener who only has D.C. mainsfacilities has, in the past, been forced to usethe D.C. type of valve or use a Universaltype receiver, but has had the limitationof the mains -supply voltage. Whilst thisis, in the majority of cases, ample to providegood reception under all conditions, the useris debarred from obtaining the same highperformance which is characterised by thebetter type of A.C. mains operated receivers.In these, of course, there is the advantage


SOME OLYMPIA SECRETS REVEALED(Continued from previous page)

of a very high voltage, obtained from asuitable input step-up transformer, and thevalve types available are, in the main,more efficient. Philips have developed aconverter which is now fitted as standardto all their D.C. mains receivers, and itconverts the D.C. into A.C. and thus thereceiver becomes, in effect, an A.C. set.The converter is built in the form of a unitse that it may easily be removed should themains supply be changed.

New Constructor ComponentsMessrs. A. F. Bulgin, the well-known

suppliers of component parts, announcethat over seventy new items will be intro-duced this season. Full details of all ofthem are not yet revealed, but they willinclude clock -face tuning dials with double -ended pointers behind glass fronts, television

The " Electric Eye "-a novel tuning indicatorfitted to an Ekco receiver.

apparatus, including a two-part control knobwhich is designed to prevent the user'sfingers from coming into contact with high -voltage points. Other high -voltage pro-tecting devices will take the form of a specialtop cap for rectifier valves, cathode-ray tubeholders, etc.

In the Wearite range, many of thealready popular components will be reducedin price, the reduction in some cases beingvery .substantial. This, in conjunctionwith the recent reduction in the price ofvalves, will prove of great advantage to thehome -constructor and will enable him toenjoy much greater benefits this winterfrom his hobby. Some new parts are alsoto be introduced to the Wearite range, andsome details of these are given on anotherpage in this issue.

Colvern ComponentsIn addition to Colvern coils of the

Ferrocart type, made in various combina-tions and also as complete tuning units(with the necessary variable condenser,etc.), Messrs. Colvern are introducing somepotentiometers, strip resistances, short-wave coils and short-wave components.For the construction of multi -valve receiverssome special aluminium screens for valvesand coils are also to be introduced,and a special, aerial, to be known as the

" Selectanet Aerial,"designed for indooror outdoor use, willalso be a newline.

Television Com-ponentsTelevision should

soon be an accom-plished fact, althoughthe continued delayshave proved verydisappointing for theconstructor and ex-perimenter, as well asthe general public.However, the possi-bility of buildingtelevision receivers inthe coming season hascreated a demand forspecial components,designed either forhigh -quality recep-tion or for use in high -voltage circuits. TheBulgin componentshave already beenmentioned, and inaddition to these theWestinghouse Com-pany are introducingtwo new rectifiers,types "H " and " J."They are designed for the supply of H.T.and G.B. for cathode-ray tubes and forthe bias in a time base unit, and weunderstand that a typical power packincorporating these devices will be exhibitedat Olympia.

Messrs. Cossor are introducing some

The tuning indicator fitted to the H.M.V.receivers is operated by the cathode-ray tubedevice shown above, and below is seen theactual indicator on the panel, showing the " in

tune" and "o$ tune" indications.I

To enable the tuning indicator to be read easily the Philips receiversemploy this type of adjustable scale. It may be raised and lowered to

the most convenient position.

cathode-ray tubes for television purposes,and, in addition, some test equipment inwhich this type of apparatus forms themajor part. They will include such itemsas a ganging oscillator and a portableoscillograph.

A new twelve -inch cathode-ray tube willalso be introduced by Ediswan, in additionto the present 5in., 7in. and 10in. models..

A Portable AmplifierMessrs. Heayberd, makers of the well-

known mains apparatus, are this yearintroducing a portable amplifier, includingspeaker and microphone. This is a 6 -wattunit, designed for connection to A.C. orD.C. mains without alteration. It isextremely compact and light in weight andis entirely self-contained, including a20 -yard length of mains cable. The inputarrangements allow for the use either ofa pick-up or microphone, and a singlefader control is fitted, with a definitecentre stop, and the only other controls arefor volume and tone. In addition to thisunit, Messrs. Heayberd will show someinteresting developments of the well-knownmains components, including transformers,chokes, condensers, etc.

Noise -free AerialsSeveral firms are specialising in 'the

production of aerial systems designed forthe elimination of man-made static. Theseare now designed for use on all -wavereceivers and are equally effective whetherused on the short waves or on the longwaveband. The Belling -Lee Eliminoiseaerial system will be sold as a complete kitof parts for one receiver, without cable,for 35s. This particular arrangement ishighly suitable for the feeding of a numberof receivers, and from eight to ten receiversmay be satisfactorily fed from it. Addi-tional " Eliminoise ' transformers may beobtained for each receiver for 17s. 6d., andthe special cable is sold at 8d. per yard.With this device each receiver fed fromthe aerial may be tuned to a differentwavelength without any inter -action be-tween the separate receivers.


August 15th, 1936. Vol. 3. No. 15.

Not a Flat FaceSOME readers have asked why it is not

possible to make the screen end of acathode-ray tube a perfectly flat face.

The prime reason for the slight curvaturearises from the bulb shape which has to beadhered to in order to allow the finished tubeto withstand the enormous stresses andstrains which arise as a result of pumpingthe tube interior clear of all traces of gas.The whole bulb has to be specially shapedto prevent the glass cracking and sorendering the tube useless. Another pointto note in this same connection, however,concerns the change of focus which wouldoccur as the spot of light traced out thecomplete raster of lines with a flat facedscreen. The beam ofelectrons emitted fromthe cathode is deflected in the final neckportion of the tube so that it has a combinedhorizontal and vertical motion. The beamis therefore " tied " to some extent at thatportion, and if the screen face was notcurved the length of the beam would alteras it moved from side to side. This wouldalter the focus of the spot and make eachline fan out at the ends if the focus adjust-ment was made to be correct at the centreof the tube. This could be corrected eitherelectrically or magnetically, but onlyintroduces an additional complication inthe initial setting up of the tube in thetelevision receiver.

Terms and DefinitionIt is understood that the British Standards

Institute is engaged on the question offinding satisfactory terms and definitionswhich can be applied to the science oftelevision. This is especially importantnow that receiving equipment is cominginto more common use, and if their recom-mendations are accepted it will do much toremove the confusion that at presentexists among engineers, manufacturers andwriters. For example, with cathode-raytubes the electrode to which a high positivepotential is applied for the purpose ofaccelerating the electrons in a streamtowards the screen so that by their impactthe screen at that point is rendered luin-inous, is referred to as the gun, the anode,the accelerator, etc. Again, the electrodeto which is transferred the modulatingsignal whose characteristic is to be con-verted into terms of light is called Wehneltcylinder, modulator, grid and so on. If atthis early stage in television's developmentit is possible to secure unanimity in theindustry insofar as terms and definitionsare concerned it will eradicate much of thedifficulty which was experienced undersimilar conditions with radio.

On the Programme SideIt is, known that the programme and

production side of the B.B.C.'s tele-vision staff have been in residence at theAlexandra Palace as from the early part ofAugust. This may be the signal for thecompletion of the first section of the pro-gramme arrangements which have been inthe planning process for some time. Oneimportant factor which needs carefulstudy is the question of make-up and

clothes. This is due to the colour sensitivityof the different types of scanners whichwill be employed, with the result thatcertain colours, particularly red, appear aswhite on the television screen showing thereproduced pictures. It is conceivable thatin time this factor will be remedied, but atpresent precautions are necessary in orderto counter the effect. It is certain thatfeature or interest items will figure largelyin the programmes, especially when relatedto topical items. Furthermore, talks willtake on an added interest, for the lecturerwill be able to illustrate his remarks withmodels or sketches. This is rather reminis-cent of several of the low -definition pro-grammes. With 'the high-definition spot-light scanner which the B.B.C. will use,similar studio scenes will be enacted ex-cept that the scanner will be in a separateroom with the " flying spot " projectedthrough a suitably positioned window.It is understood that dancing, fashionparades, lessons in various forms of sportsuch as tennis, golf, cricket, etc., people inthe news, physical exercises, and so on,will all be featured, this being quite dis-tinct from the entertainment side in whichfilms, cabaret shows, vaudeville and shortplaylets will be shown.

A Pioneer's DeathNearly forty years ago Mr. Will Day

gave public shows of the first ani-mated pictures, as they were then called.A pioneer in the film world, he becameinterested also in the early televisionexperiments and assisted Mr. Baird bothfinancially and technically with his firstexperiments. Unfortunately, lie withdrewhis support before developments hadmaterialised to a substantial stage, butlived long enough to see the birth of reallyhigh -quality television pictures which con-trasted greatly with the postage stampefforts of ten years ago. His recent deathat the age of sixty-three removes yetanother pioneer to whose efforts thiscountry owes much for its technicalprogress in many directions.

Another German EffortA few days ago the Telefunken Company

staged an important demonstration at aBerlin Exhibition. This was a projectiontelevision receiver capable of reproducingpictures on a screen four feet wide by threefeet high. The German standard of 180 -linedefinition was employed, and the pictureswere sufficiently large and bright to en-able an audience of three -hundred people towatch in comfort. Good quality pictureswere claimed to be obtained, but thedistance of the nearest observer wastwenty feet from the screen. Not onlyis this screen to be used for showing thepublic the television bibadcasts from theWitzleben station, but the events televisedfrom the big stadium at the OlympicGames were also shown on this sameequipment.

Aerial ImportanceAlthough no data is yet available

concerning the field strength of the

Alexandra Palace ultra -short-wave radiotransmitter for the vision signals, it isknown that this will vary very considerablyover the area which can be regarded as theextent of the service. Within a few miles,the strength of the received signal is likelyto be so high that a relatively inefficientaerial and feeder system will suffice forconnecting to the set itself. Anyonesituated near the border of the service area,however, is likely to have to pay morecareful attention to his installation. Anyloss of signal strength in the aerial equip-.ment will be reflected in the quality of thereproduced picture, for instead of thesignal to interference ratio being high thereverse will be the case. It is certain thatquite efficient aerial systems will be designedand made available to purchasers orconstructors of television sets, but if theinstallation is an amateur one certainprecautions must be taken. Height aboveground level is one factor coupled with themaximum distance from any source ofinterference such as the ignition systems ofmotor -cars on a main road. Whereas aninside aerial of approximately half thewavelength of the vision station connecteddirect to the aerial terminal of the set, ora simple doublet, may suffice for those closeto the Alexandra Palace, an outside aerialwould seem to be necessary in other cases.The mast itself, when possible, can bepositioned on the house roof clear ofobstruction. To the lower end of theaerial a two -wire feeder should bejoined, but only one wire is connectedelectrically to the aerial end. The secondone is left quite free and yuns parallel to thefeeder wire over the whole of its length.The distance between the wires must bekept approximately the same-about twoinches is quite satisfactory-and to ensurea parallel run over the whole length it isnecessary to insert insulating distance piecesat regular intervals. Keep this doublefeeder as clear as possible from buildings,and, furthermore, the feeder must be tuned,a process effected very simply by lengthen-ing or shortening the feeder at the setend where it joinsto the input ter-minals of the set.A little patientexperiment willb e necessary inorder to determinethe optimum con-ditions for lengthand position, butonce this has beendone the resultsfrom the point ofview of maximumsignal strengthpicked up shouldbe highly satis-factory.

A typical commer-cial Television Aerialshowing the twin

wire feeders.


Bridge MeasurementsNkeen experimenter would thinkof carrying out any detailed experi-ments or tests without the use of

some kind of measuring instrument, andin these days of low-priced test equipmentevery worth -while amateur has at least onetype of meter. We have often describedthe construction of measuring devices in

' which the main item is a milliammeter, andthis is employed in conjunction withresistors to enable various measurements

1NPUT

Fig. 1.-The fundamental arrangement of thebridge circuit.

and calculations to be made. But there isanother type of measuring device whichis very cheap to construct, and whichenables some important tests to be carriedout, and the results of the tests may be usedto operate either a visual or an audibleindicator. The basis of this type of deviceis the Wheatstdhe Bridge, but there are anumber of modern modifications which areactually only elaborations of the device,introduced to simplify certain laboratorycalculations, and they will not interest theordinary amateur. In its simplest formthe bridge will be found of the utmostsimplicity to operate, and the basis of thearrangement is shown in Fig. 1.

How it WorksIt will be seen that there are four arms,

as they are called, represented by thepoints A, B, C and D. Across two of thearms is the input circuit, and across the othertwo there is the output circuit. The fulltheory concerning the currents present inthese four arms and the method of workingout the various values will not be dealtwith in this article, but it will be sufficientto state that when the four arms,' are" balanced," and a voltage is applied tothe input circuit, no current will flow inthe output circuit. But the moment thearms are " unbalanced," a current will flowin this circuit, and this may be .used tooperate the indicating device. -

Across the points A, B, C and D theknown and the unknown components areconnected, but if the instrument' is to beused for very accurate measurements,reliable and tested comparators must beemployed. The component for measurementis connected at point A, and the remainingcomponents adjusted until the device isbalanced, when the value of the unknowncomponent is_ read off from the calibratedscales attached to the comparators, or other-wise calculated from the known values.

Input DevicesThe input supply is known as the power

source, and the output arrangement isknown as the null indicator. From thelatter Aerm it will be obvious that whenbalanced nothing will be present at the

I A Bridge -measuring Device En-

ables Capacities, Resistances andI Inductances to be Measured with j

a High Degree of Accuracy, and jI the Principle is Explained in this j

Article - - - By W. J. DELANEYL41.41.0.1M0101=M11.01110411.(1411.0.100.1.1=INAMN ANON

output, although this ideal may not bereached by the home-made apparatus.For certain measurements special impedancematching transformers will be required inorder that the power source and nullindicators may be accurately matched,and these must obviously be well screenedand prevented from affecting the balanceof the arms.

A standard L.F. oscillator may be usedat the input, a buzzer may be employed, or asimple dry battery, the exact sourcedepending upon the component beingmeasured. Such items as a beat -frequencyoscillator will only be needed for valvetests and similar high-class arrangements.

Output DevicesFor the output (when a D.C. input is

employed) the simplest device is a gal-vanometer, but when an A.C. input is used,

Fig. 2.-A simple bridge for resistancein theoretical form.

a pair of ordinary headphones may beemployed, connected through a suitabletransformer, or the two output terminalsmay be joined to a valve amplifier to operatea loudspeaker' or other powerful indicator.It will generally be found that headphonesform the most reliable form of indicatorbecause the ear is so sensitive to slightchanges and to the differentiation between

ASU DE WIRE

fundamental tones and their harmonics.A'valve voltmeter may also be employed,

but is not so sensitive.Standards or Comparators

For standards by which the unkpowncomponents are measured, ordinary com-mercial components may be used, and thenormal standard of accuracy of moderncomponents will be found suitable for allordinary purposes. Where a higher degreeof accuracy is required the makers ofresistors, condensers, etc., will supplycomponents guaranteed to '1 per cent. plusor minus at a slight extra cost. The keenexperimenter will obtain a few resistances oflow values and build up a decade or similarbox with a ten -point switch such as theBulgin component reviewed last week, sothat the required values may easily beascertained. A high-class variable condenserwith a 0 to 100 scale firmly attached to thespindle will serve for condenser measure-ments, and a suitable laboratory type instru-ment may \be obtained at a very reasonablefigure from Electradix Radios. This firmcan also supply ex -Government resistanceboxes which will enable various rangesto be obtained very simply.

Standard inductances are not so easy toobtain in the smaller ranges, but a series ofsmall plug-in coils may be built, and thestandard formulm will enable the desiredranges to be obtained, although for

this type of measurement it willgenerally be found that ordinarycommercial components may be used,as exact inductances values are notusually required by the ordinaryexperimenter.

measurements

AccuracyThe accuracy of the bridge de-

pends, of course, upon the accuracyof the standards which are used, andif the three arms, -and the input andoutput circuits are so arranged thatno interaction takes place a mostefficient test instrument will be ob-tained.

A simple Bridge for resistancemeasurements is shown in Figs. 2 and 3,and the balance is obtained when R1over R2 equals R3 over R4. A length ofresistance wire is stretched between

points A and B with a metre rule alongside.The values of the resistances R3 and R4 willbe proportional to the points A C and C Band thus may easily be calculated. By insert-ing the unknown resistance between pointsR1 and G and a known resistance betweenG and R2 the value of the unknown resist-ance may be calculated from the formulamentioned above.

METRE RULE.,

WOODEN BASEBOARD

R

l'

-,.... -

--............S.-..

-..-- r A.,

--, .-')/a 0000000 . ttttt 1 lllllll filial .1,11111111 E01111iIIII llllll 110111111 lllll 111111111111111111110 Mt ,mm .m in RIM 1111.11101

- - ...=,,...METRE RULE -

Fig. 3. -The practical arrangement of Fig. 2.

B.

August 15th, 1936 PRACTICAL AND AMATEUR WIRELESS561

=1=14,0571.1II

Od111111111111144

o "\\ '111// 0

IT is now generally understood by listenersthat the average domestic receivercannot reproduce programmes exactly

as transmitted. This is due partly to thefact that in order to achieve the necessarydegree of selectivity the sidebands have tobe more or less severely cut, thus producingattenuation of the treble response, andpartly because certain components, forexample, loudspeakers, do' not have a trulylinear response to all frequencies in the

When using aconverter-thebroadcast re-ceiver mustreceive atten-tion to improve

quality.

audible range. It is also realised that inmany receivers, mainly of the commercialtype, these deficiencies are compensatedfor in a greater or less degree by " tonecorrectors," whereby the parts of theregister which are below par are boosted,or those which are too prominent are toneddown.

The normal problem, then, for the listenerwho wishes to doctor his set with the objectof obtaining better reproduction, is to devisea form of synthetic qtality on these lines,in order to undo some of the harm done byexcessive selectivity and the lack ofunif comity in audio -response in variouspartrof the set,

But, as has been explained in previousarticles, the ultra-short-wave sound accom-paniment to the television programmes will,

in due course, provide opportunities forthose possessing the necessary equipmentto receive sound broadcasts under con-ditions which do not necessitate unduecutting of the sidebands in the cause ofselectivity, and in consequence will offergreat possibilities for real quality repro-duction.

It is not really. difficult to design andbuild a quality receiver when receptionconditions do not impose the need for a highdegree of selectivity, and success in thisdirection depends almost entirely upon

/NO

SHORT AVESECTION

Artificial Aids to Quality on the U.S. Waves-Part 1

This Article makes Special Reference to Ultra -Short-wave Reception

Using a Home Set in Conjunction With an U.S.W. Adapter or Converter

By .H. J. BARTON CHAPPLE, B.Sc.

correct proportioning of the circuits and the

use of a really good speaker. No doubt,large numbers of enthusiasts will produce

ultra -short-wave sets of this type during the

coming season.In General Terms

But for every amateur who builds aspecial ultra -short-wave quality set therewill be many who, at first, will_ contentthemselves with an ultra -short-wave adaptor

or converter connected on to the normalhome set. This set may not be a qualityreceiver in the true sense of the word, butrather one designed to reproduce a reason-ably, large number of medium -wave and

long -wave stations.It would be a great

pity if such listeners were debarred from

testing the joys of good quality reproductionas made possible by the ultra -short -waves,

and it is therefore desirable to examinethe question with a view to suggestingmeans whereby the home set can be adapted

for quality reception in connection with

an U.S.W. adaptor or converter. The

number of different types of set is so greatthat explicit instructions which are of

universal application cannot be given, butby discussing typical examples it will bepossible to show the owner of any set of

average type how he can approach theproblem.

There are really two main types of

problem to be discussed, the first being thatconfronting the listener who intends using

an ultra -short-wave adaptor, and the

second that which faces the user of a con-verter. The former, being thesimpler, and being also applicableto the owner of a converter, will betackled first. As most amateursare aware, a short-wave or ultra -short -wave adaptor is a radio -frequency unit, either a simpledetector or a high-frequency anddetector combination, operatingat short or ultra -short wavelengths,the output of whichisintended to beapplied to thedetector output ofa domestic radioset, so that onlythe low -frequencyamplifying sectionof the domestic setis used for ultra -short -wave repro-duction. Since thedesign of the ultra -short -wave unit isnot within the scopeof this article, itwill be assumed

A standard all -wave receiver-theGraham Farish. Multiwave Three.

that the adaptor to be used is such thatthe sidebands are not suppressed, to adegree which will mar reproduction so that,other things being e,pial, the qualityobtained will depend entirely upon thedesign of the L.F. side of the domestic setand upon the eharacteristics of the speaker.

On the L.F. SideThe problem, therefore, resolves itself

into deciding what improvements the -

listener should make in the L.F. section ofhis receiver in order to permit it to takeadvantage of the quality possibilities ofultra -short waves. Generally speaking, thelow -frequency stages of domestic receivershave little wrong with them from the pointof view of design. The main. Point toconsider is-does the set, as at presentconstituted, give really good quality ongramophone reproduction ? If the answeris in the affirmative then apart from one ortwo small details the user should be content. .

In the first place it is necessary to dis-connect any device, such as needle scratchfilter which may have been embodied inthe L.F. side, as the presence of this willdeprive reproduction of part of the all-important upper register. Then, if a tonecontrol, consisting of a conde,nser andvariable resistor is connected across theoutput; this should be turned to full" brilliant," i.e., with the resistance portionall" out." It is not wise to remove thiscontrol entirely, as the presence of thecondenser is a safeguard against highvoltage surges in the pentode circuit in the


562 PRACTICAL AND AMATEUR WIRELESS August 15th, 19 36

in the vicinity of 12R0 Rome (25.4 m.)consists of four notes (G, B, D, G), and whichrepeated ad lib. may last some five or tenminutes before speech is picked up. Itemanates from PPQ, Sepetiba (Brazil), on25.71 m. (11,670 kc/s), working a radio -

SHORT WAVE SECTION(Continued from previous page)

event of the speaker being inadvertentlydiscomiected. Another point which wouldmilitate against good quality is small out-put, and this applies more particularly tobattery sets where economy in H.T. supplyis important.

In this connection, it would be a goodplan to replace an ordinary power triode orpentode with one of the new high -sensitivitypentodes which, while giving a much greateroutput for a given signal, are particularlyeconomical. In any case, for qualityreception it is recommended that the H.T.voltage to the output be raised to themaximum rating of the valve, making surethat the grid -bias is adjusted to suit, andto be fairly liberal in the matter of anodecurrent. Remember that this not onlyimproves the quality of the output, but thatmost speakers give better reproduction onfairly large outputs than when starved ofoperating power.The Speaker

This brings us to the speaker itself, andwhatever adjustments are made to the set

itself the final result is often limited to theperformance characteristics of the speaker.The average small speaker built into thecabinet of a receiver gives very littleresponse above 5,000 cycles, while itscramped position usually means poor bassreproduction and the substitution of truebass by box resonances. If a good qualityspeaker is available, connect it to theextension terminals of the set and mount itin a good baffle not less than three feetsquare or a properly -designed cabinet withnarrow sides. If no extension circuit isfitted to the set, now is the time to arrangeone, and when doing so it is as well to fit aswitch to enable the internal speaker to becut out of circuit.

If, however, in spite of these things, theL.F. side of your set is not really satisfac-tory, it is advisable to go over the circuitto see where improvements can be made.It may be assumed that a straightforwardlow -frequency amplifier, using good com-ponents of the correct values, introducesvery little distortion. Without knowingwhat the actual circuit happens to be, full

'instructions cannot be given, but thefollowing few hints may help. A small L.F.

transformer, especially if of old type, shouldbe resistance -fed. R.C. coupling should bechecked to see that the anode resistance is ofthe correct value-say, three times theimpedance of the previous valve. Tryvarying the value of the coupling con-denser in such stages. In some commercialbattery sets the L.F. stages are deliberatelysomewhat overbiased in order to reduceH.T. consumption, and the adjustmentsmentioned above will produce considerableimprovement. Distortion is sometimesintroduced by the presence of high -fre-quency currents in the L.F. side of the set,and an H.F.filter or a grid -stopper resistancebetween the detector and the output stagewill probably make a lot of difference.

Finally, the best quality input and thebest quality output will be spoiled if thereare unwanted noises superimposed, and inthe interest of quality any measures whichyou had promised yourself to apply to avoidelectrical interference should be appliednow, and in addition the receiver should begiven an overhaul to discover any badjoints or other small defects liable tointroduce noise.

(To be concluded)

WITH the civil war raging ....4.0..............0.0........in Spain, the posses-sion of radio stations

is a valuable asset to both parties,and much use is made of them. Leaves from aTune in to the short waves afterB.S.T. 21.00 and you will pick upone or two broadcasts on un-familiar

Short wave Logwavelengths over and L.

above those to which we have -

been accustomed on the regular channels.On about 31 metres I have heard a newsbulletin given out in English, Spanish andPortuguese, and from the announcementI gathered that the Radio Club of Tenerife(Las Palmas), previously working on41.61 m., has adopted a more favourablewavelength. This station is on the airnightly at G.M.T. 23.00. If you want allthe news every night-although, as youwill see, you will get different versions ofthe same incidents-tune in Moscow (25 m.)CT1AA, Lisbon (31.09 m.), and EAQ,Madrid (30.43 m.). Both Moscow andMadrid give you English translations oftheir news bulletins, as does Tenerife.

Listeners now report the reception ofbroadcasts from Addis Ababa (Ethiopia).I doubt very much whether they are beingpicked up direct, although as the stationis now in Italian hands and has beenentirely reconstructed to give it a powerof 10 kilowatts, there is always this pos-sibility. Of the four transmitters, twohave been converted for both radio tele-graphy and telephony. You may care tonote particulars-namely, ETA, 25.09 m.(11,955 kc/s) now IUC and ETA, 39.37 in.(7,620 kc/s), bearing the call -sign IUB.Tests have been recently made in bothspeech and music with a view to a relayof native entertainments for rebroadcastby Rome and other Italian medium -wavestations. Possibly they have been heardthrough IBR, San Paolo (Rome) on20.89 in. (14,360 kc/s), 15 kw., which isthe channel used for the wireless link.The call heard was " Addis Ababa perRadio San Paolo," and the tests werepreceded by a series of notes on oscillatingvalves, a signal which is now being adopted

telephony service with Europe. A simul-taneous transmission is made throughPPU, on 15.58 m. (19,260 kc/s), wherethe same interval signal is heard. Whencalling, the woman operator informs youthat it is RIO (de Janeiro).

Radio Podebrady (OLR) is on the air.If the name sounds mysterious, let me tellyou that it is the Prague short-wave trans-mitter to which many references have beenmade during the past few months. Thestation is a 34-kilowatter capable of beingboosted up to 56 kilowatts, and destinedto relay the main Czech programmes foroverseas listeners. So far tests of speechand gramophone records only have beencarried out on 19.58 in. (15,320 kc/s) ;25.54 m. (11,740 kc/s) and 49.06 m.(6,115 kc/s), but the station is also author-ised to use 13.99 in. (21,450 kc/s), 19.70 m.(15,230 kc/s) ; 25.26 in. (11,875 kc/s) ;25.51 m. (11,760 kc/s) ; and 31.57 m.(9,504 kc/s), so you may occasionally pickup trial broadcasts on these channels.The announcements are made in severallanguages, including English, and the

quality of the transmissions isexcellent.

Another newcomer recentlylogged is Batavia (Java), on 19.80m. (15,150 kc/s) ; it is a trans-mitter owned and operated bythe N.I.R.O.M., which runs thePMN and other regular Nether-lands East Indies short-wave andmedium -wave broadcasters.

From Geneva comes good news for bothmedium- and short-wave listeners, to theeffect that the first all -world concertarranged by the U.I.R. will be furnishedby the United States of America onSeptember 20th at G.M.T. 21.00. It isto be a star programme to which both theN.B.C. and C.B.S. organisations jointlycontribute. On this occasion, as an intro-ductory note, I understand, Europeanlisteners will be given an opportunity ofhearing the roar of the Niagara Falls.The entertainment which follows is to berelayed to a number of Old World stations.

In this connection, as regards the servicefor overseas listeners, it is interesting tolearn that a new method of recording wire-less programmes was recently demonstratedat Washington (U.S.A.). Although thesystem used is one which employs a speciesof sound -film, it is claimed by the inventorsthat an entire day's programme from abroadcasting station can be recorded on areel the size of an ordinary spool of thread,and that the cost is an exceptionally lowone.

041 *** oiBRITISH LONG-DISTANCE LISTENERS' CLUB

ENROLMENT FORM (See announcement on page 563).Iwish to enrol my name as member of the British Long-distance Listeners'iClub, it being clearly understoodthat no financial obligation is thus incurred. I am interested in long-distancelist ening and have* a short -

have notwave receiver at present in use. I am especially(medium -wave*

interested in {short-wave; listening.ultra -short-wave

Full Name (Block letters)

Address

by a number of commercial transmitters. ; *Strike out words not needed.One of this kidney which may puzzle you Optional

Please forward me pads of 50 log -book sheets price ls. 6d.

badge price 1.. each

pads of 50 verification forms pr:ce Is. W.cheque forfor which I enclose postal order . ..... s No. 60. .0 0. 0. *0. Or *0 .10. Oa


The British Long-

Distance Listeners' ClubThis handsome Badge, inred, blue, and gold, may beobtained by Members for

Is. post free.

563

AN IMPORTANT ANNOUNCEMENTTO EVERY READER

In the interests of long-distance listening, and especially for the development of short-wave

world-wide reception, we are taking over the British Long-distance Listeners' Club which

was inaugurated by the Wireless Magazine. The following details concerning this club

are given for- the benefit of those new readers and others who are not already familiar with

this great community of long-distance listeners, and all who find enjoyment and thrills in

the searching out and reception of long-distance transmitters should join the club and take

advantages of the many benefits which form part of the scheme.

THE purpose of the Club is solely to bring togetherall those listeners who specialise in the reception

of stations situated in distant parts of the world.

It is intended to form a community of kindred minds ;

and its aims are the encouragement of DX reception,mutual help, and comradeship.

The B.L.D.L.C. has no commercial aims. Membership

is free. Members can, therefore, still belong to allother similar associations with similar aims withoutincurring any additional financial responsibilities through

their membership of the B.L.D.L.C. In order to give

members the opportunity of exchanging ideas,

the services of the entire technical staff of

PRACTICAL AND AMATEUR WIRELESS are placed

at the service of every member. PRACTICAL AND

AMATEUR WIRELESS, furthermore, will set aside in

this periodical a special section in which, besides

reports of reception, instructive articles, informa-

tion, etc., the internal affairs of the Club willbe discussed.

To enable listenersto make systematicrecords of theirlistening hours, theClub has had speciallog -book formsprinted. These con-tain spaces for alldetails necessary for

serious receptionand will provide thelistener in afteryears with a veryvaluable record.Furthermore, to aidClub members in

No enrolment or member-

ship fees.Organisation centred inGreat Britain.Standardised log -books andverification sheets and

badges available for mem-bers at reasonable prices.Regular report in "Practicaland Amateur Wireless."Interchange of ideas with

fellow members:

O. NO 0.

the compilation of their verification reports and toenable comprehensive records of such reports to bekept, special forms have been designed for the

purpose.

Useful StationeryIn addition to these two forms, the publishers are

also issuing stationery which, like the log -book andverification report forms, can be obtained at a verylow cost.

If you are keen on short-wave searching, or evenif you only listen on the medium -wave band andare interested in the reception of long-distance

stations, you should join the Long-distance Listeners'Club and take advantage of all its benefits. By

wearing the neat badge you will be able to recogniseother members, and this will afford its own intro-duction and enable you to discuss matters to yourmutual advantage.

All readers interested should fill in immediately theapplication form onpage 562 of this issueand post it to us. Wewould point out onceagain that member-ship of this Clubis entirely free. Ad-dress your lettersto:-

$

Advantages of Membership(6)

(7)

(8)

(9)

Members in same district

placed in touch with one

another when desired.

Special meetings and visits

to be arranged.

Regular problems for short-

wave listeners.

Members' competitions and

numerous other advantagesto be announced.

... 4444444 ... ..... .1

The Secretary,British Long-distance

Listeners' Club,8-i 1, Southampton

Street, London,W.C.2.

564 PRACTICAL AND AMATEUR WIRELESS August 15th, 1936Fo041=11.0411110.04=.11-.Mlitl.111irtHEMK

O

HIGH -FREQUENCY AMPLIFICATIONAn Explanation of the Purpose of Ian H.F. Amplifier and

of Inter -valve Coupling.

IN dealing with low -frequency trans-formers last week it was explainedthat wireless valves are voltage -

opefated devices, their purpose being toincrease the voltage of the signals received.In doing, this, they amplify the signal.But whereas the low -frequency stagesamplify the low -frequency voltage which

Fig. l.-Diagrammatic circuit showing theH.F. coupling.

comprises the actual sound impulses, theH.F. stages amplify the combined low andhigh -frequency voltage in the form inwhich it strikes the receiving aerial. Forpresent purposes it can be considered thatthe impulses " handled " by the H.F.valves are of high frequency only, since thelow -frequency (or modulation component)is so completely and thoroughly mixedwith the so-called carrier wave.Extending the Range

The L.F. section of the receiver servesto increase the volume of reproduction bymagnifying the low -frequency voltage,but the H.F. amplifier does not necessarilyprovide greater volume, but increases therange of the set. The reason for this is thatthe detector cannot operate at fullefficiency unless the signal voltages fed toit exceed a certain minimum figure. Thus,

a if the input to the detector were below that; minimum, satisfactory reproduction couldI not be obtained however much Iow-a frequency amplification were provided.

It is for this reason that the high -fre-quency amplifier is so useful in extendingthe range of the receiver ; it increases the

; strength of weak or distant signals to suchan extent that they can allow the detector

a to function. Of course, in the case ofsignals which are above the minimum

I required by the detector and below thea maximum handling capacity " of the

detector, H.F. amplification does providea certain increase in signal strength. This

a is a point which is not always fullyappreciated.

of the Systems

The Inter -valve CouplingLet us consider the circuit arrangement

of an H.F. amplifying valve, such as thatshown in Fig. 1. It can be seen that atuning circuit is connected between theaerial and earth, and that a lead from thisis taken to the grid of the screen -grid valveshown. In the anode circuit of the valveis shown a simple rectangle, this represent-ing the coupling between the first andsecond valves. Before dealing with theform which this coupling can take, let usconsider its purpose. In the first place itmust offer a very high impedance to thesignal, because if it did not signal currentswould simply pass through it, through thehigh-tension supply, and back to ear th

H C .

0111111.114MINNEINHNIMIO.M1111111.1.111M-1,41.1111N

being received, and is at a maximum onlyat one particular wavelength or frequency. aIt is for this reason that so-called aperiodicor untuned coupling is not very efficient, Ialthough it can be used with moderate asuccess, especially when it is not requiredto apply reaction.

A Tuned CircuitThe tuned circuit, shown in Fig. 4, is

theoretically ideal, because its impedance $

I

is practically constant at all wavelengthsto which it is tuned. Moreover, the im-pedance of a high -frequency circuit isalmost infinity to the frequency to whichit is tuned. This is the basis of most high -

frequency coupling circuits, although theactual connections shown in Fig 4 aremodified in the practical arrangement.The most important alteration concernsthe connections to the tuning condenser,which is joined between the anode of thevalve and earth, instead of to H.T.+.By using these connections it is possibleto employ a gang condenser of which allthe moving vanes are earth connected.The alteration does not affect thebehaviour of the tuned circuit in mostcases because there is a complete circuitfrom the earth line through to the H.T.-1-end of the tuned -anode coil by way of thehigh-tension supply. In many instancesthis circuit is made to have a still lowerresistance due to the connection of a large -

1

1

IHT+ i

I

0002MFD.

H.T*

GR/0

0005

GR/t)

-0002MFD.

I

E. HT- E HT- E.Figs. 2, 3 and 4 (left to right).-Resistance-capacity, choke -capacity, and tuned -anode

couplings.

In other words, they would be " lost " andwould not be passed on to the secondvalve. The coupling must also provideanother function-that of preventing thehigh-tension voltage from being applied tothe grid of the following valve in the formof a very high bias voltage.

Forms of CouplingThe coupling can comprise a fixed

resistance, an H.F. choke or a tuned cir-cuit, as well as a condenser and grid leakas shown in Figs. 2, 3 and 4. it will beseen that all of these are very similar, butthey produce different effects. In thefirst place, the resistance causes a pro-nounced voltage drop, especially if it hasa sufficiently high value to provide abarrier to the H.F. currents, and, there-fore, it is impracticable. The choke ismuch better, because it provides therequired impedance to H.F. currents,whilst offering a resistance of only 100ohms or so to the direct, or high-tension,current. But it is by no means perfect,due to the fact that its impedance variesaccording to the wavelength of the signal

1011.141.111.41,10111.4=1,0111.04111114EN14 ..114.(14mei

H. r -

capacity fixed condenser between earthand H.T. , as shown in Fig. 5.

Tuned GridA modification of the Fig. 5 circuit is

shown in Fig. 6, where the choke couplingis combined with a tuning circuit joinedbetween the grid of the following valveand earth. This arrangement is known as

E

.0002MR).

IF). GRID

.0005Agra

1/.1"-Fig. 5.-A practical modification of the

tuned anode circuit shown in Fig. 4.

August 15th,. 1936 PRACTICAL AND AMATEUR WIRELESS

ir.o................,.........,.,.................-......,..,......................,....-"....................,-.I tuned -grid coupling, due to the fact that winding is included in the anode circuit

the tuning coil and condenser are actually of the valve. The secondary circuit is I

1 in the grid circuit. The H.F. choke acts tuned by means of one section of the gang

I as a barrier to high -frequency currents, condenser and feeds into the grid of the 1

i thus diverting them to the tuning circuit. following valve. It will be clear that byIj

Theoretically, this niethod of coupling having a greater number of turns on the

is not quite as efficient as the tuned -anode secondary than on the primary winding, 1

1

- a step-up effect would be produced. And jHTi since the secondary must be of such a size I

that it tunes to the wavelength of the 1signal being received, the number of turns 1

i1

I1 design a small extra degree of amplifica- jcan be obtained, although by careful

::

00 is a limit to the degree of step-up which I2

0005

MFD

MED.tion can be obtained by using fewer turnson the primary than on the secondary 1

a=

is definitely regulated. Thus, the step-up I

1_1..... GRID

effect must be secured by reducing thesize of the primary. Because of this there j

0

I

winding. The difference in results which jcan be obtained in this manner is small, I

Iand there is little practical difference in fefficiency between the amplification j

I Fig. 6.- The popular tuned -grid circuit,

1which is a combination of the arrangements 1

shown in Figs. 3 and 5.H.T+

1 system, but it has the practical advantage -:-

of being more stable that is, unwanted1 pscillation is not as readily provoked. In -0002 Mr' D. I

i this case it must be observed that when the 1

following valve is a leaky -grid detector, 1

1 two fixed condensers are required : onej between the anode of the H.F. valve and-1- the end of the tuning coil, and another 00172 GRID :

I between the coil and the grid of the MFD.

1 detectorI

i! The High -Frequency Transformer1 Another modification of the basic I

I circuit is shown in Fig. 7. Here the choke /

,..! and tuning coil are replaced by a double -1 wound coil, or high -frequency transformer. E Hx- i

j In many respects this behaves like thelow -frequency transformer which was Fig. 7.-Tuned H.F. transformer

I described last week, and the primary coupling. I

LI 1.m.11-010.0....111104.0.01410141011=0.-011.10.0411110-04=0.1140MHNMPO.01.1..1141M.04.1.11004=1.0411NNun. NJ

obtained when using tuned -grid, tuned- -anode, or tuned -transformer coupling.

0005MFD.

PROGRAMME NOTES" Filmusic "

THE fifth in the series of six gramophonerecitals featuring the best-known

tunes from films of the past seven yearswill be broadcast on August 21st.

" The Tune You Heard "MARTYN C. WEBSTER will present a

Programme under this title for theNatribnal programme on August 18th. Itwill consist of a selection of original tunesfrom recent Midland productions. Thevocalists will be Marjery Wyni, WebsterBooth and the Southern Sisters, withReginald Burston conducting the RevueOrchestra. The Southern Sisters had theirfirst broadcast in a Martyn Webster pro-duction from London.

Broadcast from the ZooIT is Scotland's turn on August 22nd to

entertain all listeners to the Children'sHour in Scotland, England. and XortliernIreland. A'number of microphones will beset up in the Zoological Park, Corsthrphine,Edinburgh, to receive the familiar voices

and strange language of Sundra, theelephant ; Meek and Mild, the hyenas ;Susan, the seal ; a regiment of penguins ;the Ape Family, and a chorus from thelions' den.

Ulster Grand Prix

AS inpast years, this thrilling race,

which is the grand finale of theBritish Motor Cycle racing season, and oneof the most important events in the calendarof sport, will form the subject of a broadcastcommentary on August 22nd. The race isrun over the famous Clady Circuit, whichis 201 miles in length, and must be coveredtwelve times by the 500 c.c. machines,eleven times by the 350 c.c's and ten timesby the 250 c.c's.

From the start the course is slightlydownhill and practically straight for sixmiles ; then comes a right-angle bend atThorn Cottage, followed by a left -and -right at Aldergrove. Three miles of fastbends lead to the most difficult corner onthe course-at Greenmount, where ridersenter an extremely narrow and somewhatrough road.

565

BRAND NEW GOODSNOT SURPLUS

NEW TIMES SALES Co. offer the following at an extremely lowprice. Each is entirely brand new or shop soileB only. We guaran-tee that every component is a genuine condtructor's componentand must not be confused with the multitude of manufacturers'surplus or rejects which are at Present on the market. Orders

over 5)- Carriage Paid. C.O.D. fee extra.

N.T.S. ALL WAVE 3 KITRecommended by Mr. F. J. CAMM

WAVERANGD 12.2,000 metres. This Kit will enable you tobuild a set that will receive the whole wide world direct, for a very

small outlay. Includes everything for Immediate assembly,including 1 Slow Motion Dial ; 3 6 -pin Coils, 12/26, 260/910, and1,000/2,000 metres t 1 6 -pin coil base ; 3 9 -pin baseboard mountingvalveholders ; 1 short-wave HIP Choke; 3 variable condensers,.0001, .0002, and .00016 MFD ; 2 Terminal mounts ; 4 terminals ;2 L.P. Transformers; 2 Bred resistances; 3 fixed condensers;3 component brackets ; 1 switch, 1 metal -sprayed baseboard ;1 coil connecting wire ; 1 wiring diagram.

CASH or C.O.D.CARRIAGE PAID

Less ValvesSet of 3 recommended British valves, 10/-. Recommended full-size permanent magnet M/O speaker, 10(-. Extra coils for inter-mediate wavelengths, as follows : 9/14, 22(27, 41/94, 76j170 metres.2/- each. 150(325, 490/1,000 metres, 2(6 each.

N.T.S. SHORT WAVEUP-TO-DATE ADAPTOR KIT

CIRCUITListen to America and all the World

DIRECT for only 15/-.,COVERS 12-94 METRES. Complete Kit of parts tobuild a reliable short-wave (adaptor for use with

any BATTERY set.Kit comprises all parts for instant assembly. Includingmetal -sprayed baseboard, 2 variable condensers, .00016, .0001

MFD, 2 baseboard mounting 4 -pin holders. short-wave H.F.choke, grid leak, fixed condenser, adaptor

tig-in coils, 12/20, 22/47, and 41(94 metres,plug, terminal mount, two terminal,, 3-4 pinpi

151 component bracket, Slow motion drive,Trimming condenser, connecting wire and Cash or C.O.D.wiring diagram. Built in one evening. Carriage paid.

1.

N.T.S. MARVEL S.G. 3 KITSIMPLICITY

EFFICIENCYComprises a newly -developed air.cult, modem to the minute andusing tested and matched com-ponents, each specially selectedfor efficient performance.The Kit includes 2 -gang air -spaced condenser of advanceddesign; Knob dial; wavewound coils on bakelisedformers; super L.F. Trane-former ; solid dielectric re-action condenser ; completewith ready -drilled chassis and alt necessary valve-

print showing How to Built the Marvel 0.0.3holders, small condensers and resistances- (Blue -

716eupplled FREE with each Kit)Set of three British valves, H.F. Pentode, Det., Super Power, 20/0Recommended full-size permanent magnet T6/0 Speaker, 110/-.

(11P.M. M.C. SPEAKEROBARGAIN at 716

Manufacturers' stock of BRAND NEW PermanentMagnet Moving -Coll Speakers at less than cost. 0 -in. -Cone. Large magnet and complete with input trans-former suitable for Power, Super -Power or Pentode.State which type required when ordering. Cash orC.O.D. 7/6 Carriage 6d. extra).

66 (Pr. W.15), LUDGATE HILL, LONDON, B.C.&Please send full details of

together with complete lists Of N.T.S.and accessories.

I NAME

EST. 1924

Kite, components I

. .

ADDRESS


Let Us Send You


It gives full information regarding variousI.C.S. Courses of Instruction in Radio work.I The Radio industry is progressing with

amazing rapidity. Only by knowing thoroughlythe basic principles can pace be kept with it.,I.C.S, Instruction includes American broad-,psting as well as British wireless practice. Itis a modern education, covering every depart-ment of the industry.


dealing with the Installing of radio sets and,an particular, with their Servicing, which to -dayintimately concerns every wireless dealer andthis employees. The Equipment Course givessound instruction in radio principles and'practice.' There is also a Course for the WirelessSalesman. This, in addition to inculcating the,art of salesmanship, provides- that knowledge.which enables the salesman to hold his ownwith the most technical of his customers.


We will be pleased to send you details andfree advice on any or all of these subjects.'Just fill in, and post the coupon, or write inany other way.

4.11mi onm. .2 vs. am, Imm. mom mim. sal Nom ma= =NI IMP



Without cost, or obligation, please send me your" Radio " booklet of information about the CoursesI have marked X

COMPLETE RADIOn RADIO SERVICINGj:( RADIO EQUIPMENT

{ RADIO SERVICING AND SALESMANSHIPf WIRELESS ENGINEERING

L1 EXAMINATION (state which)

Name Age

Add- ecs

11.MIHNI414., .,=141.4MEN.II04.11.1.41.111=.0.=.43.0

RE,PLIES IN BRIEFThe following replies to queries are given in

abbreviated form either because of non-compliance= with our rules, or because the point raised is not ofIgeneral interest.LICro.ffspettoIni

D. B. (Mill Hill). The receiver is of American originand we do not know of any firm who can supply a blueprint in this country.

J. H. (Marsh). Your earth connection is probablyinefficient. Experiment with different earths in anendeavour to improve conditions.

A. W. (Slaithwaite). We cannot understand why youexperienced the difficulty mentioned, unless you selectedthe wrong type of valve. ;You must make certain thatthe different makes of valve have exactly the samecharacteristics, and your guide in the particular casementioned is the Mutual Conductance.

A. T. A. D. (Weimer). The valve is an obsoletetype. At 150 volts on anode and screen and with 15volts grid bias, the anode current is 14 mA and thescreen current 2.7 mA. The A.C. power output isonly 400 mllliwatts, and the optimum load is 10,000ohms. Is your 22D valve overloaded ? This wouldaccount for the other trouble mentioned.

D. E. (No address). No, you should certainly includethe Driver valve for best results. The circuit is other-wise quite in order.

G. H. (Norwich). We regret that we cannot followyour remarks, and should be glad to receive a wiringdiagram or theoretical circuit, together with yourcomplaints.

J. A. (Dublin). Any flex may be used, but thematerial usually fitted by the makers is made up of ametal foil interwoven with cotton threads. You shouldat least hear two stations on the set referred to, Dublinand Cork. Belfast and other stations may be heardunder favourable conditions.

G. H. (Dorking). If the eliminator will deliver 30 mAit is suitable. A similar output would be requiredfor the push-pull circuit mentioned.

D. G. B. (Berkhamsted). Generally speaking thedevice is not very efficient. If a good coil is obtainedquite good results may be obtained provided that therequired current is of a low order. Otherwise, a specialinduction coil must be used, and these are not obtain-able. In the case referred to a special unit has beenmade for the purpose.

P, T. B. (Cefferd). We do not recommend the pro-cedure outlined by you. The difficulties of runningfrom one cell on the accumulator may be overcome byusing a series resistance from the entire battery, or byusing each cell in turn to level up the discharge rate.

J. McC. (Lurgan). The valve may be used andfollows normal practice. The additional pins are forconnection to the suppressor grid and the metallisedsurface, and these should be joined direct to earth.

R. C. (Belfast). The volume control may have avalue of .25 or .5 megohms.

J. G. R. (Ipswich). We have no blueprints of such areceiver in a modern form. The four -valve midgetpublished last week may prove suitable, or the MidgetClass B Portable, Blueprint AW. 389, which employsa class B stage, may prove suitable. The latter is notso compact as the latest receiver, but there is no blue-print for this particular set.

J. F. (Cardiff). We cannot suggest improvementsfor a commercial receiver, and if it proves unsuitableand is not up to specification, you should communicatewith the makers.

F. G. S. (Rubery). We have several circuits of thetype mentioned, but none with] the particular conden-ser, and coil named. You may be able to select a suit-able circuit from our blueprint list and incorporateyour own coils, but we cannot give you instructionsfor carrying out such modification.

D. O'C. (Twickenham). The coils used in the LeaderThree were two Universal (Wearite) components, andthe condenser was a double Nugang, Type A, made byJackson Bros.

G. R. (King's Lynn). It is possible to use certainrectifiers in the manner outlined, but this is not inaccordance with the 'recommendations of the I.E.E.The output from the set in question (when the outputvalve is fully loaded) is 3 watts.

E. G. C. (N.W.2). In view of your proximity to theLondon transmitters we suggest a superhet. As yourpresent components would not then be suitable weadvise you to dispose of the present receiver and obtainthe new parts for a modern superhet such as the £4Superhet, for either battery or mains operation.

J. A. (Gwernymynydd). The trouble is fairly commonand is known as L.F. instability. A reversal of theconnections to either the primary or secondary gener-ally cures the trouble by making the two signals out ofphase. It is, of course, better to prevent the troubleby correct design and operation than to cure it by thisdevice.


Club Reports should not exceed 200 words in lengthand should be received First Post each Mondaymaiming for publication in the following week's issue.

The West London Radio SocietyAT the committee meeting held on

July 24th it was decided that nofurther meetings should be held by theSociety until a later date in August, as theattendance at such meetings would probablynot be as good as it has been up till theend of July.

It was also agreed that in future morefield days should be held on land, than onthe river, as they have been during Juneand July.

Any communication should be addressedto the hon. sec., H. A. Williamson, 22, Cam -bourne Avenue, West Ealing, W.13.

ATALOCUESEC EIVED

To save readers trouble, we undertake to send oncatalogues of any of our advertisers. Merely state, ona postcard, the names of the firms from whom yourequire catalogues, and address it to "Catalogue."PRACTICAL AND AMATEUR WIIIELEsS, Geo. Newnes,Ltd., 8-11, Southampton St., Strand, London, 1V.C.2.Where advertisers make a charge, or require postage.this should be enclosed with applications for catalogues,No other correspondence whatsoever should be enclosed.FERRANTI RADIO VALVESTHE latest copy of the Ferranti valve list, No. R.115,

is just to hand. Twenty-seven pages (91n. by6in.) are devoted to the various types issued byFerranti, and in addition to the essential character-istics of the various types, typical circuits are givenfor every individual valve. Characteristic curves areincluded, and in the case of the output valves thedynamic characteristics are shown. The catalogueincludes a diagram of base connections, table of pinconnections, complete list of the valves and prices, anda table of valve equivalents. The catalogue may beobtained free on application either direct to Messrs.Ferranti or to us.COSSOR RECEIVERS

BOOKLET B.30 has just been issued by Messrs.A. C. Cossor, and gives all details of the new

range of receivers. These range from the popularMelody Maker, a battery three-valver at £5 19s. 6d.,to Model 537, a console radiogram at 16 gus. There aretable radiograms, superhets and straight sets in variouscabinet types to suit all requirements, and sepia -tonedillustration?; of each model are given iu the catalogue.I.S.W. CLUB NEWS LETTERTHE International Short Wave Club, London

Chapter, have sent us a copy of their monthlypublication the News Letter. This gives variousdetails of the forthcoming club features, late stationnews, and a short-wave review. The July issue containsan article on the Frequency Monitor, in the series" How to become an Amateur Transmitter." A copyof the News Letter will be sent to readers on applica-tion to the secretary, A. E. Bear, 10, St. Mary's Place,Rotherhithe, London, S.E.16, if they will enclose ld.stamp.

A FINE BOOK FORTHE BEGINNER!

AND A USEFUL PRESENT

EVERYMAN'SWIRELESS

BOOK(2nd Edition)

By

F. J. CAMM3/6 or 3/10 by post from Geo. Newnes,Ltd., 811 Southampton Street, Strand,

London, W.C.2.


LETTERS FROMThe Editor does notnecessarily agree withopinions expressed by his

correspondence..

" Sound Recording for the Amateur "SIR,-The article by L. Ormond Sparks

on " Sound Recording for theAmateur" in the August 1st, 1936, issuemust have been welcomed by many experi-menters in this work, which in recentmonths has experienced a great revival ofinterest.

As one who is devoting much of his titheto the subject, may I offer a few miscel-laneous hints, and a correction of a slighterror ?

It is usual to make first test recordingson aluminium, or aluminium -alloy blanks,as they are cheap and easy to obtain, butit is advisable to cover the blanks with alubricant. This can be, say, paraffin oil,shoe cream or a good wax polish, and athin layer should be smeared over theblank before cutting. The object is to fillin the " pores " of the blank, thus makingthe surface more homogeneous and alsoreducing the frictional resistance to therecording stylus. In the article referred toone particular blank is recommended but,in addition, I would like to draw readers'attention to the " Simplot " blanks of theV.G. Manufacturing Co., Ltd., and a flexibletype invented by Dr. C. G. Lemon. Theformer consist of a glass base, with a blacksurface coating of a gelatinous compositionwhich, after cutting, is hardened andpolished by fluids. The latter are made ofa cellulose material, which is thin andtransparent, and are softened, hardenedand polished with fluids. These blanks arenot yet marketed, but will shortly beavailable at an inexpensive price.

Another serious difficulty that will bemet with is fluctuation in recording turn-table speed ; this trouble must be avoidedas it will introduce objectionable " wows "into the reproduction. An electric motorwith a high torque is necessary, and asuitable model just released is the SimpsonHeavy Duty Electric Turntable, which is

a synchronous type, priced at five guineas.Remember that a stroboscope, or strobo-scopically marked turntable rim, whenilluminated by a neon lamp working offA.C., will enable the speed constancy, orotherwise, to be checked.

Finally, regarding the error. On page 513,column 3, paragraph 3, line 6, the term" positive counterpart " should read " nega-tive counterpart.' This will be realised, aswhen the copper " master " is stripped offthe recorded wax blank, which is positive,the grooves appear as ridges, or, one mightsoy, in. relief. The, correct order in pro-cessing is as follows ; recorded wax blank,or " filled blank " (-1- ), copper " master "(-), series of copper " mothers " (+ ), andrequired number of stompers, workingmatrices or dies (-), and the presseddisc (+ ).-DONALD W. ALDOUS, M.Inst.E.(Ilford, Essex).

SIR,-I was very interested to read thearticle by L. Ormond Sparks on

" Sound Recording for the Amateur,"having studied the subject for, some years,but I feel I must question the statementconcerning the distancebetween groovewalls being governed by frequency.

Surely:the amount of s* swing of the

READERSAll letters must be accom-panied by the name andaddress of the sender (notnecessarily for publica-

tion). _

stylus is dependent upon amplitude and ?totfrequency, which only governs the shape andnumber of fluctuations per given distance.

Admittedly, with most amateur recordingsystems, if there is any tendency to " overmodulate," and consequently cut throughthe walls of the groove, it is at the lowerfrequencies that this occurs.

There is a reason for this inasmuch asthe popular cutting head or, in manycases, a converted pick-up has a markedrising bass characteristic.

Wishing continued success to yoursplendid paper.-Cucu, L. APPLEBY (Short -

lands, Kent).

Modifying Coil ConnectionsSIR,-Wanting to try the 2 -valve circuit

on page 445 of PRACTICAL ANDAMATEUR WrRELtss dated July 11th, andhaving no six -pin coils, I hit on the followingdodge. The low potential ends of all threecoils are connected to one pin, on a 4 -pinformer, and the other three pins take thehigh potential ends, thereby doing awaywith both 6 -pin former, and the base. Theuse of such a coil has one snag, viz., thereaction condenser has to be placed at thelive end of the coil ; it also nebessitatesbushing the panel if it is a metal one.

There is no disadvantage in having oneend of the aerial in common with oneend of the grid coil, as both would normallygo to earth, and leave the reaction windingto connect in the normal manner. In thatcase the aerial would go to the loose endof the aerial coil.-H. FIELDING (Oldham).

CUT THIS OUT EACH WEEK

-THAT in a modern testing laboratory theindividual circuits of a receiver are ganged bymeans of cathode-ray tube indicators.-THAT an ordinary A.C. voltmeter may beused to measure the audible output of a re-ceiver and may be calibrated to show the gainor loss in decibels.-THAT the maximum theoretical amplifica-tion of an H.F. stage cannot be obtained asinstability occurs before the maximum gainis reached.-THAT special valveholder spacing is adoptedfor high -voltage power -output valves, and aspecial base is employed.-THAT although the core of the moderntransformer is extremely small compared witholder models, the inductance is Just as highowing to the use of special metals for the core.-THAT high -efficiency coils in some modernreceivers are wound on glass formers, and litzwire is employed for the winding.

The Editor will be pleased to consider articles of apractical nature suitable for publication in PRACTICALAND AMATEUR WIRELESS. Such articles should bewritten on one side of the paper only, and should containthe name and address of the sender. Whilst the Editordoes not hold himself responsible for manuscripts, everyeffort will be made to return them if a stamped andaddressed envelope is enclosed. - All correspondenceintended for the Editor should be addressed : The Editor,PRACTICAL AND AMATEUR WIRELESS, George Newnes,Ltd., 8-11, Southampton Street, Strand, 0%0.2.

Owing to the rapid progress in the design of wirelessapparatus and to our efforts to keep our readers in touchwith the latest developments, we give no warranty thatapparatus described in our columns is not the subject ofletters patent.

PETO-SCOTTComponents, Kits, Receivers or Accessories for Cash or C.O.D. as

on our own system of Easy Payments. C.O.D. Orders value eve,10/- sent carriage and post charges paid (OT. BRITAIN ONLY).

THE NOVEL MIDGETKIT if A SP Cash or £3 . 6 . 6

Carriage PaidAuthor's lEt of first speeiBed parts, less valves, headphones, speaker,

batteries, and ease.or 12 monthly payments of ob.. 4 specified valves £2. 7, 6.

fto-Scoc6 1937 ALL -WAVE S.G.3

for £7 . 15 . 0 4 WAVEBANDS14-31, 28-62, 200-550and 900-2,100 Metres.Variable -Mu H.F. Pentode,High Efficiency Detector.Harries High Efficiency Dia-tortionless output PentodeValves, Double Ratio slow-motion self indicatingcolour coded AirplaneDial, Sin. Tone CorrectedM.O. Speaker. Latest typelow - capacity switch withsilver - plated self - cleaningcontacts. Ganged flail -BearingSbic'cled Condensers. Combined

Volume Control, On -Off Switch. 11.T.001131111 p(lon 10 in/a, H.T.i 1..T. andG.B. Batteries.. Waltalt veneeredcabinet (illustrated). Aerial eluipment.READY TO PLAY. post Couponfor Free Illustrated Folder.Cash or C.O.D. Carr, Paid, ,E7/15.Balance in 18 monthly payments

of 9/6.RADIO FOR THE MILLION, "NEW

MASTER THREE," 3 -valuer. CompleteKit of components with Mullard valves. Cash Wilgior C.O.D. Carriage Paid, £111713.Balance in 10 monthly payments of 4/.. Only

1936 STENTORIAN SPEAKERSModel 362. P2.1. Speaker. Cash or C.O.D.Carr. Paid 22/210, or 2/6 down and11 monthly payments of 41-. -

Model 361 Cash or C.O.D. Carr. Paid.51/12/6, or 2/8 down and 11 monthlypayments of 8/ -

Any W.B. Model on similar Easy 'Forms.

Send

2/6DOWN

PETO-SCOTT Co. Ltd 77 (E4.W.16)City Rd., London,BC.1(Clerkentrell 9406)

a711tiorielvn.

Many of the mostrevolutionar changesin condenser designhave first seen thelight of day in ourlaboratories.

Therefore every 'con-structor who buysJ. B. does so withthe assurance that heis buying an articlewhich has incorporatedevery modern deviceas well as one whichwill give untiringservice for many years.

JACKSON BROTHERS(LONDON) LIMITED,73, BT. THOMAS STREET,

LONDON, S.E.1.

Telephone : Hop 1837


Radio inItaly

DURING the next`Fiera delLevante," the greatRadio Exhibition willbe inaugurated, in a

special stand of enormous proportions. Themost important Italian firms will be repre-sented and will exhibit their latest models.

The firm Allocchio and Bacchini has con-structed a portable carbon microphone(model 1864), fitted with a holding device orhandle, cord and plug connection, destinedto all uses which call for a high output whilstavoiding great amplification, and for whicha very critical response curve is not abso-lutely indispensable.

The " Soc. Scientifica Radio BrevettiDucati " has presented a complete series ofapplicances for the elimination of radionoises, both at the receiver and in theappliances. This is claimed to be the firstseries of such silencing devices which hasbeen produced in Europe.

The latest novelties in sound -film tech-nique will be demonstrated in the Open AirCinema installed in the " Giardino delleFontane Luminose," at the fourth CinemaExhibition at Venice, which is beingheld from August 10th to August 31st.The most interesting exhibit will be cine-matographic stereophony, i.e., the per-spective reproduction of sounds, which'gives the impression of listening to musicperformed by a large orchestra. Thisdiffers, in its Italian realisation, from whathas been done until now abroad. In the Open Air Cinema some ten loud -speakerswill be employed, four large -cone giantdynamics, for the reproduction of low notes,two snail -shaped giant exponential hornsfor the reproduction of the central scale,and, lastly, four direct special type exponen-tial horns for the reproduction of highnotes (up to 12,000 cycles). This tri-phonicensemble, based on the three wave scales(low, medium, high), includes three ampli-fiers (one for each scale), which allows of thecomplete selecting and amplifying in-dependence of each scale. In the threeamplifiers, a special tone control allows ofcontrolling the breadth of the three acousticbands transmitted to the three groups ofloud -speakers, and this follows exactly thephonic characteristics of the film in con-nection with the ambient sterophonic effects.

Shrewsbury Floral FeteTHE Shropshire Horticultural Society is

in its sixty-second year and the Showit will hold in the beautiful Severnsidepark known as " The Quarry " will be itsfifty-sixth (there was a gap during theWar years and 1919). In that period thetotal takings have been £353,851, anddonations totalling £25,639 have been madeto various societies, chiefly concerned withthe beautification of the town of Shrews-bury, and for the purchase of the old Castle.There are one hundred and seventy-fiveclasses and a number of valuable cups,'including the £100 Perpetual ChallengeTrophy, presented by Alderman Charles'Aveling, of Southport, in recognition of helpreceived by Southport Show from theShropshire Society. C. H. Harvey, a formerMayor of Leominster, and Honorary

By JACE

Secretary of the Horticultural Section of theold Leominster Show, will give an eye-witness account of the Shrewsbury Fête onits first day, relayed from the Midlandtransmitter, August 19th. On the secondday (August 20th) the concert by theMassed Bands of the Irish Guards, theWelsh Guards, and the Royal Air Force willbe broadcast in the National programme.the conducting being shared by Flight-Lieut. R. P. O'Donnell, M.V.O. ; Lieut.J. L. T. Hurd ; and Major Andrew Harris,M.V.O. (Senior Director of Music of theBrigade of Guards). For nearly forty yearsMassed Bands have been the distinctivefeature of the musical entertainment atShrewsbury Fête.

in a raised box on the inside of the bend.He will be able to see the machinesapproaching the corner down a gentleincline at very .high speeds, rounding thecorner, and roaring away past the aero-dromes. Aldergrove Corner is one of theparticularly exciting points of the course,and Graham Walker will have plenty ofmaterial on which to exercise his powers ofgraphic description. Raymond Glendenningwill give the commentary from the GrandStand near the famous hairpin bend atClady Corner. From this point he willdescribe the general scene, the start, and thefinish, as well as the passage of machinesduring the race.

The commentary is to be broadcast onthe National as well as the Norelitrn rfelandwavelength, from 1.45 to 2.30 and againfrom 4.15 to 5.15. Listeners will also beinterested to know that on the Fridayevening before the race-that is August 21st-D. A. Boyd is to give a short talk," Ulster Grand Prix Prospects."

Yehudi Menuhin, the brilliant young violinist, is now away in Cali-fornia and will not be heard again for two years. The only music whichyou can hear, therefore, is from gramophone records, the latest of which is

" SchOn Rosmarin" and " Tambourin Chinois."'

Ulster Grand PrixONCE more the time of the Ulster Grand

Prix is coming round ; the timewhen Northern Ireland is for a few days themotor cyclists' Mecca. It was in 1928 thatthe Ulster Grand Prix was won at anaverage speed of more than eighty miles anhour, and it then sprang into fame as theworld's fastest motor -cycle race. It beganin 1922 as a small amateur affair and it hashad a romantic rise to fame during the lastfourteen years, until to -day it is an excitingand thrilling event in which the whole ofUlster seems to take a keen, almost personalinterest. From Belfast, as from othercentres in Northern Ireland, there willagain be a great exodus of people in almostevery kind of conveyance, all bound for thecourse on August 22nd.

The B.B.C. arrangdments for broad-casting of running commentaries on therace are now almost complete. This yearthere will again be two commentators, butthe second commentary point is to bemoved from Muckamore to Aldergrovecorner, a sharp bend just before the coursepasses the Royal Air Force station. HereGraham Walker, himself a former well-known Grand Prix rider, and winner ofmany motor -cycle events, will be stationed

PromenadeConcerts, 1936REFERENCES

have been madein the Daily Pressto the collectivesubscription s y s -tern, or season -ticket pool, whichenables a group ofpeople to club to-gether to buy aseason - ticket forthe PromenadeConcerts. This sys-tem has met withuniversal approval,which is not sur--prising when onereflects that aseason - ticket forforty-nine concertscosts only £117s.6d.-(i.e. 9d. per concert,instead of 2s.) sothat six people shar-ing, and dividingthe ticket amongthem selves, caneach go to one con-

cert a week throughout the season at a totalindividual cost of 6s. 3d.

It is incorrect to say that the B.B.C.looks upon the scheme with disfavour ;on the contrary, on the principle of " themore the merrier," it welcomes it as beingcalculated to increase considerably the saleof season -tickets.

THE NORTHERN POLYTECHNIC!

)THE next session at this institute opens

on September 7th, and in the latestprospectus received from the institute wenote that the Radio Technology sectionmay be attended both by day students andevening students. This section works inconjunction with the Music IndustriesCouncil, the Wireless Retailers' Association,and other influential musical and associatedbodies, and provides a very complete seriesof lectures covering all branches of radioand television. Students are prepared forthe diplomas of the Music Industries Counciland the Institute of Wireless Technology.

Full particulars of the course, fees, etc.,'may be obtained on application to thePolytechnic, Holloway, London, N.7.

August 15th; 1936 PRACTICAL AND AMATEUR. WIRELESS 569

COMPONENTS TESTED IN OUR NEW LABORATORY

New Goltone LinesMESSRS. WARD & GOLDSTONE an-

nounce some interesting new lineafor the coming season, several of which willappeal particularly to the home con-structor. ,Wel,have already reviewed theBulldog connectors (see our issue datedNovember 16th last), and although thesehave universal application for the experi-menter, when being used in high -voltagecircuits such as may become quite commonwhen television apparatus is being dealtwith, there will be a risk of severe shocksbeing felt unless the clip is protected. Smallrubber cowls are therefore being produced,designed especially to fit over the threesizes of clip. They slide over the body ofthe connector, are flexible, and respond tothe movement of the springs and thus actas a protection not only against shock butalso against corrosion. A hole is providedfor the entry of the cable or connectinglead. Prices range from 2d. to 40.

Another interesting item is the double -pole 2 -pin fused plug designed for any smallelectrical appliance such as a wirelessreceiver, electric clock, etc. These plugs areinterchangeable with B.E.S.A. standard5 -amp. 2 -pin plug bases, and incorporate acartridge fuse in each pole. These blow atapproximately 2 amps., thus saving thehouse fuse and avoiding a sudden plungeinto darkness in the event of a breakdownduring the evening. The plugs are availablein round or oblong patterns, the price ofeach type being respectively Is. 4d. andls. Spare fuses cost 3d. only.

Electro-dynamic ConvertersTHE Electro Dynamic Construction Co.

announce that they have carriedout much research with a view to findingsuitable anti -interference filters for usewith converters and the new ultra -sensitiveshort-wave sets. As a result they haveproduced a filter which is satisfactory forall wavebands from 10 to 2,000 metres.In future this filter will be fitted as standardto all their converters without extra charge,and the machines will be designed so thatthey will be suitable for tropical use.

Magnum Multi -contact SwitchesTHE range of Magnum silver -contact

multi -point switches has now beenextended 'and includes eleven standardtypes, having from 2 to 12 pairs of contacts.These are available with two, three, four,five or six positions and the prices rangefrom 2s. 6d. to 6s. Special short-wavemodels are available at slightly increasedprices, varying from 3d. in the case of thesmall model to ls. for the large model.In addition to these standard lines, theswitches may be obtained in any desiredcombination to order, and double -sidedswitches are available at an extra cost of10 per cent. on the above prices. For specialcombinations a chart is available on requestand the user may indicate the detailsrequired in an unmistakable manner. Themakers are Messrs. Burne-Jones & Co.,Ltd., Magnum House, 309-317, BoroughHigh Street, S.E.1.

Marconiphone 3 -Valve Battery SetANEW 3 -valve battery receiver was

released on the 4th of this month byMarconiphone, and the model will be knownas Model." 294." This is of the T.R.F.type, similar in many ways to Model" 282," but has a much greater measure ofefficiency and incorporates a very greatlyimproved cabinet. The appearance of thisreceiver leaves nothing to be desired andreveals a further development of the metalframe wooden cabinet which has provedso popular of late. The list price of thereceiver is 7i guineas and it may be obtainedon convenient hire purchase terms.

The main circuit details are as follows :S.G. H.F. valve transformer-coupled to atriode detector, auto -transformer coupledto a high -efficiency pentode valve, with aspecial tone -correcting circuit. Threecontrols -tuning, volume and masterswitch, with a supplementary sensitivitycontrol. Tuning scale marked in wave-lengths in metres, provision for extraspeaker and pick-up. Maximum undis-torted output 400 mW., with a H.T. andL.T. consumption of 8 mA and .4 amps.respectively.

New Mazda PentodeMESSRS. EDISON SWAN announce a

new battery valve to be included inthe Mazda range. This is a battery pentodeof the high -slope type, with a 2 volt .3 amp.filament. The maximum anode and screenvoltage is 150, and the normal workingvalues are 120 volts for anode and screen,2.5 volts grid bias, anode current 5 mA.The optimum load is 19,000 ohms, and theprice is I ls. The base is of the standard5 -pin type.

The new Goltone plug and rubber cowl forthe Bulldog connectors.

New Polar ComponentsSOME new lines are to be included in the

Polar range of components, and anew type of ganged condenser has beentested by us. This is known as the " Bar "type, and is much smaller than the usualganged unit. It is not entirely enclosed,but is fitted with end plates and a solidbar running through the unit at top andbottom. The entire framework is of steel,but the vanes are of aluminium. Theminimum capacity is very low, and it wasfound that when the unit was screweddown, even when the screw holes weredeliberately made out of line, the structure

did not pull out of truth and thus causefouling of the vanes. The sections werefound to be very accurately matched, andthe trimmers are conveniently placed ontop. In the standard models bakeliteinsulation- is provided, but when desiredspecial models may be supplied withceramic insulation. The prices for a two -gang straight or superhet standard modelis 12s., and for a three -gang straight orsuperhet 17s. 6d. The prices for the specialceramic model are 14s. and 20s. respec-tively.

The remaining new lines include a single -type ball -bearing condenser, a mica -dielectric trimmer and midget condensersin the ordinary and compax types.

New Ferranti ValvesTO the Ferranti range two new mains

valves are now to be added. Oneis a double -diode triode of the universal(A.C.-D.C.) type, with a 5 volt .3 amp.heater, type SD, and the other an A.C.variable -mu pentode, type VPT4B. Thedouble -diode is intended, of course, foruse as a combined detector and automaticvolume control valve, the separate typeof valve providing an undistorted signalfree from interaction with the L.F. section,and permits the use of a high delay voltagewithout a reduction of the available anodevoltage at the output valve which occurswhen the diodes are operated from theoutput valve cathode.

The VPT4B has a 4 volt 1 amp. heater,and is rated for 250 volts on the anodeand screen voltage up to 100 volts. It hasa higher slope than the VPT4 valve anda shorter grid base. The price is 12s. 6d.

The Fuller AccumulatorFULLER Accumulators announce

high -capacity accumulator of the2 volt type, rated at 24 A.H. at the 20 -hourrate. This is of the standard Fuller type,having dimensions of gins. by gins. andis pins. high. The type reference is FMG,and the price is 10s. The range of H.T.dry batteries made by this firm is to begreatly extended for the coming season,and a number of special models intendedas replacements in standard receivers willbe included.Wearite Components

ANEW volume control potentiometeris announced by Messrs. Wright and

Weaire, and some of the older componentshave now been improved and modified.The new volume control is of the carbonelement type, and is available in variousvalues from 5,000 ohms to 2 megohms.It may be obtained with or without aswitch, and the price is 4s. or 5s. The coilstypes P, Q, R, S and T, are also improvedand reduced in price, costing only 7s.now. Short-wave coils, types A, B and C,are reduced to 2s. 6d., and a new model,type D, covering from 97 to 200 metres,is now introduced. The H.F. choke, typeHFJ, is now available with a pig -tailconnection and costs 2s. 6d., whilst type11F0 is reduced from 4s. 6d. to 3s. 6d.Short-wave choke, type is alsoreduced in price, and now costs only2s. 6d. The remainder of the popularcoils, transformer switches, etc., arc stillcontinued, and in the range of test in-struments a new signal generator is to beintroduced, but at the moment of goingto press no details are available. No doubtthis unit will be produced in time for theRadio Exhibition.

THE BEST WEEKLY FOR CYCLISTSTHE CYCLIST

2d. WEEKLY


All -Wave Unipen (pentode) ..Two -valve : Blueprints, Is. each.Four -range Super Mag Two (D,

Pen) .. 11.8.84

Three -valve : Blueprints, 1s. each.Selectone Battery Three (D, 2 LF

(trans.)) ..Sixty -Shilling Three (I), 2 LF

(LC. & trans.)) 2.12.33Leader Three (SG, D, Pow.) ..Summit Three (11F Pen, D, Pen) 18.8.34All -Pentode Three (HF Pen, D

(pen.), Pen) .. . 22.9.34Hall -Mark Three (SG, D, Pow.)Hall -Mark Cadet (D, LF Pen

(R.C.)) .. 10.3.35F. J. Camm's Silver Souvenir (HF

Pen, D (pen), Pen) (All -WaveThree) . .. 13.4.35

Genet Midget (D, 2*LF (trans.)). .June '35Cameo Midget Three (ll, 2 LF

(trans.)) .. 8.0.351936 Sonotone Three -Four (HI

Pen, HF Pen, Westector,Pen) .. 17.8.35

Battery All -Wave Three (n, 2 LF(11.0.)) . .. 31.8.35

The Monitor (HF Pen, 1), Pon) .. 8.2.86The Tutor Three (HF Pen, D, Pen) 21,3.36The Centaur Three (SG, D, P)

Four -valve Blueprints, Is. each.Fury Four (2 SG, D, Pen)Beta Universal Four (SG, D, LIP,

Cl. B) _ 15.4.33Nucleon Class B Four *iSG, D

(SG), LFS,

CI. B)Fury Four uper (SG, SG, D, Pen)

6.1.34

Battery Hall -Mark 4 (HF Pen, D,Push -Pull)

Mains Operated.Two -valve : Blueprints, 1s. each.A.C. Twin (D (pen), Pen)A.C.-D.C. Two (SG, Power) .. 7.10.33Selectone A.C. Radiogram Two

(D, Pow.)

Three -valve : Blueprints, 1s. each.Double -Diode -Triode Three (11F

Pen, D.D.T., Pen) .. .. 10.6.33D.C. Ace (SG, D, Pen) .. 15.7.33A.C. Three (SG, D, Pen) ..A.C. Leader (HF Pen, D, Power) 7.4.34D.C. Premier (HF Pen, D, Pen) 31.3.34Ubique (HF Pen, I) (Pen), Pen) .. 28.7.34Armada Mains Three (111' Pen, lb,

Pen) .. 18.8.34F. J. Camm's A.C. All -Wave Silver

Souvenir Three (HF Pen, D,Pen) .. . . 11.5.35

"All Wave" A.C. Three (D, 2LF(R.C.)) .. 17.8.35

A.C. 1936 Sonotone (HF Pen, HFPen, Westector, Pen) .. 31.8,35

Four -valve : Blueprints, Is. each.A.C. Fury Four (SG, SG, D, Pen)A.C. Fury Four Super (SG, SG, D,

Pen) .. . -A.C. Hall -Mark (H Pen, D, Push -

Pull)Universal Hall -Mark (HF, Pen, D,

Push-pull) 9.2.35

SUPERHETS.Battery Sets : Blueprints, 1s. each.£5 Superhet (Three valve)F. J. Carom's 2 -valve Superhet

(two -valve) .. .. 13.7,35F. J. Camm's £4 Superhet .

Mains Sets : Blueprints, Is. each.A.C. £5 Superhet (three -valve)D.C. £5 Superhet (three valve) 1.12.34Universal £5 Superhet (three


hot 4 . 11.1.36


Three -valve : Blueprints, Is. each.Experimenter's Short-wave Three

(SG, D, Power) . . The Prefect 3 (D, S LF, 110 and

Trans.) ..

15.9.34

8.2.36

Practical and Amateur WirelessBLUEPRINT SERVICE

PRACTICAL WIRELESSSTRAIGHT SETS. Battery Operated.

One -valve : Blueprints, 1s. each.Date of Issue. No. of

BlueprintPW31A

PW3613

PWIO

PW34APW35PW37

PW30PW41

PW48

PW49.PM2

PW51

PW53

PW55PW61PW62PW64

PW11

PW17

PW34BPW34C

PW46

PW18PW31

PWIO

PW23PW25PW29

PW35CPW35BPW30.4.

PW38

PW50

PW54

PW56

PW20

PW34D

PW45

PIV47

PW40

PW52PW58

PW 43PW42

PW44PW59

PW60

PW38A

PW30A

PW63

PORTABLES.Three -valve : Blueprints, is. each.I'. J. Camm's ELF Three -valve

Portable (HF Pen, D, Pen)


D, LF, Cl. B)

MISCELLANEOUS.S.W. Converter -Adapter (1 valve)

16.5.36 PW65

PW12

PW48A


Blueprints, 6d. each.Four -station Crystal Set .. , . - AW4271934 Crystal Set .. .. .. AW444150 -mile Crystal Set .. .. - AW450

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, ls. each.B.B.C. Special One-valverTwenty -station Loud -speaker


Two -valve : Blueprints, is. each.Melody Ranger Two (D. Trans)Full -volume Two (SG., Dot., Pen)B.B.C. National Two with Lucerne

Coil (D. Trans)Big -power Melody Two with

Lucerne Coil (SG, Trans) .. -Lucerne Minor (D. Pen) .. . , -A Modern Two-Valver July '36

Three -valve : Blueprints, ls. each.Class -B Three (D, Trans, Class B)New Britain's Favourite Three

(D, Trans, Class B)Horne -Built Coil Three (80,

Trans) ..Fan and Family Three (D, Trans,

Class B) . ,

£5. Ss. S.G.3 (SG, D, Trans) .1934 Ether Searcher : Baseboard

Model (SG, D, Pen) ..1934 Ether Searcher Chassis

Model (SG, D, Pen)Lucerne Ranger (SG, I), Trans)Cossor Melody Maker with Lucerne

Coils ..P.W.H. Mascot with Lucerne Coils

(D, RC, Trans) ..Mullard Master Three with

Lucerne Coils .. .

£5 6s. Three : De Luxe Version(SG, D, Trans) .. .

Lucerne Straight Three 011,Trans) ..

All Britain Three (HF Pen, D,Pen)" Wireless League " Three (IIF

Pen, Pen) ..Transportable Three (SG, D, Pen)£6 6s. Radiogram (D, RC, Trans) -Simple tune Three (SG, I), Pen) Juno '33Economy -pentode Three (SG, D,

Pen) .. Oct. '33" W.M." 1934. Standard Three

(SG, D, Pen) -£3 3s. Three (SO, -D, Trans) .. Mar. '34Iron -core Band-pass Three (SG, D,

QP21) Juno '341935 £6 Os. Battery Three (SG, I),

Pen) .. -P.T.P. Three (Pen, D, Pen) . June '35Certainty Three (SG, D, Pen) . Sept. '35Minitube Three (SG, D, Trans) .. Oct. '35All -wave Winning Three ($G, 'D,

Pen) Dec. '35

22.4.33

15.7,33

25.11.332.12.33

20.1.34

19.5.34

3.11.34

AW387

AW449,

AW388AW392

AW3 77 A

AW338AA W420WM409

AW386

AW394

AW404

AW410AW412

AW417

AW419AW422

AW423

AW337A

AW424

'AW435

AW437AW44S

AW451\VM271WM318WM327

WM337

WM351WM354

WM362

WM371WM389\VM393WM390

WM400

Four -value : Blueprints, 1s. 6d. each.65/- Four (SG, D, RC, Trans) .. AW370' A.W." Ideal four (2SG, D, Pen) 16.9.33 AW402

2 H.F. Four (2SG, D, Pen) . - A W421Crusaders' A.V.C. 4 (2HF, 0.,

QP21) .. . .. .. 18.8.34 AW445(Pentode and Class -13 Outputs for

above : blueprints 6d. each) . 25.8.34 AW445..trSelf-contained Four SG, I), LIP,

Class B) '33 W11331Lucerne Straight

.........Aug.iour(SG, D, LP,

Trans) .. .. .. - - W51350£5 Ss. Battery Four (IF, 0,

2LF) . , . Feb. '35 WM381The H.K. Four _ .. - Mar. '63 WM384The Auto -Straight Four .. .. April '36 WM404The Request All -Waver .. June '36 W61407

Five -valve :.Blueprints, Is. 6d. each.Super -quality Five (211F,

Trans) May '33New Class -B Five (280, *D,

Class B) . Nov. '33Class -B Quadradyne (260, D, LF,

Class B) Dec. '331035 Super Five (Battery Super -

het) .. -

WM320

WM340

W51344

W111373

These blueprints are full size. Copies of appro-priate issues containing descriptions of these setscan in most cases be obtained as follows :-" Practical Wireless " at 4d., " Amateur Wire-less " at 4d., " Practical Mechanics " at 70., and" Wireless Magazine " at 1/3d., post paid. Indexletters " P.W." refer to " Practical Wireless "sets, !! P.M." to " Practical Mechanics " sets," A.W." refer to " Amateur Wireless" sets, and" W.M." to " Wireless Magazine " sets. Send(preferably) a postal order (stamps over sixpenceunacceptable) to " Practical and Amateur 'Wire-less " Blueprint Dept., Geo. Newnes, Ltd., 8-11,


Mains Operated.Two -valve : Blueprints, 1s. each.Consoelectric Two (D, Pen) A.C. 23.9.33Economy A.C. Two (D, Trans) A.C. -Unicorn A.C./D.C. Two (D, Pen) Sept. '35Three -valve : Blueprints, 1s. each.Horne -lover's New All-eleetrie

Three (SG, D, Trans) A.C. . ,S.G. Three (SG, D, Pen) A.C. -A.C. Triodyne (SG, D, Pen) A.C. 19.8.33A.C. Pentaquester (111? Pen, D,

Pen) A.C. 23.6.34Mantovani A.C. Three (HF Pen,

D, Pen) A.C. -£15 15s. 1930 A.C. Radiogram

(HF, D, Pen) .. .. Jan. '30

AW403WM286W61394

AW383AW390A W399

AW43O

W112374

W11401Four -valve : Blueprints, 1s. 6d. each.All Metal Four (2 SG, D, Pen) , July '33 WM329Harris Jubilee Radiogram .. May '35 WM386

SUPERHETS.Battery Sets : Blueprints, ls. 6d. each.Modern Super Senior WM375Varsity Four .. Oct. '35 WM395Mains Sets : Blueprints, 1s. 611. each.1934 A.C. Century Super A.C. .. 10.3,34 AW425Fleptode Super Three A.C. .. May '34 NW313035:" W.111." Radiogram Super A.C... -1935 A.C. Stenode _ Apt. '35 WM385

PORTABLES.Four -valve : Blueprints 1s. 6d. each.Midget Class B Portable (SO, D,

LF Class B) . 20.5,33 A W380Holiday Portable (SG, D, LF,Class B) 1.7.33 AW393

Family Portable (HF, D, RC,Trans) .. . 22.9.34 AW447Two H.F. Portable (2 SG,QP21) . June '34 W111303

Tyers Portable (SG, D, 2 Trans) Aug. '34 WM367SHORT -WAVERS -Battery Operated.

One -valve : Blueprints, 1s. each.S.W . One -valve converter (price 6d.) - AW329S.W. One -valve for America . - AW429Roma Short -waver AW452Two -valve : Blueprints, 1s. each.Ultra -short Battery Two (SG det,

Pen) Feb. '36 WM402Home-made Coil Two (D, Pen) - AW440Three -valve : Blueprints, 1s. each.World -ranger Short-wave 3 (D,

110, Trans) .. -W3

Experimenter's 5 -metre Bet (D,Trans, Super-regcn) 30.6.34 AW438A55

Experimenter's Short -waver . . Jan. 19,'35 A W403The Carrier Short -waver July '35 WM390Four -valve : Blueprints, 1s. Gd. each.A.W. Short-wave World Beater

(BF, Pen, D, RC, Trans) . -Empire Short -waver (SO, D,

Tram) .. -Standard Four -valve Short -waver Mar. '35 W613133Superhet Blueprint, Is. Gd.Simplified Short-wave Super Nov. '35 WM317

Mains Operated.Two -valve : Blueprints, 1s. each.Two -valve Mains Short -waver (D,

Pen) A.C. -" W.M." Band -spread Short -waver AW453

(D, Pen) A.C./D.C. . Aug. '34 W111308"W.31." Long -wave Converter - WM380Three -valve : Blueprint, 1s.Emigrator (SG, ll, Pen) A.C. ,,WM352.Four -valve : Blueprint, Is. Gd.Standard Four -valve A.C. Short-

waver (SG, D, It0, Trans) ,Aug. '35 WM301MISCELLANEOUS.

gnthuslast's Power Amplifier (cloy June '35 WM337Listener's 6 -watt A.C. Amplifier(1/6) . , Sept. '35 WM302

Radio Unit (2v.) for WM392 (Is.) Nov. '83 W61398Harris Electrogram (battery am-plifier) . .

De -Luxe C*o*ncert A.C.Electio*- De °, '15 WM311gram Mar. '38 W51403New style Short-wave Adapter(1s.) . .. June '35 WM388Trickle Charger (6d.) .. Jan. 5, '35 AW462Short-wave Adapter .. .. Dec. 1, '84 AW456Superhet Converter

B.L.D. L.C. Short -Wave Converterpea* 1,'34 AW457

(1s.) .. /If ' 3 6 WM405Wilson Tone Master -(1s.) June '86 WM406The W.M. A.C. Short -Wave Con-

vertor (1.s.) .. July '30 WM4.08

August 15th, 193 6 PRACTICAL AND_ AMATEUR WIRELESS 571

All -wave Set" I have a commercial all -wave set

(6 -valve superhet) which works perfectlyon M.W. and L.W. On the short waves,however, it will work perfectly ua to about35 metres, and then the remainder of thisband is absolutely silent. The 48 to 150metre band works perfectly up to about110 metres. The silence does not alwaysoccur from 35 metres upwards. Sometimesit starts at 45 metres and at the oppositepoint on the 135 metre band. If the needleis rotated into the silent area, the set turnedoff for a while and then turned on again,sound is heard for a moment and almostimmediately dies away. I wonder if youcan suggest the cause of the trouble."-S. B. (Stamford Hill).

WE do not as a rule like to suggest thecauses of faults in commercial

receivers, as this generally leads the user toattempt to cure the trouble and, if un-successful, the set is then returned to themakers and the result is that they do notcare to undertake the work after the sethas been tampered with. Furthermore, thecost of repairs will be increased as damagemay be done through ignorance of theexact circuit details. It is always desirablein the case of a commercial receiver toreturn it to the makers or take it to theirnearest service agent so that it may beattended to. In this particular. case, how-ever, the fault is an interesting one and it isinteresting to note that the trouble can beremoved by switching off. As signals areheard for only a very short time the inferenceis that either a resistance is faulty andvaries in value when a certain current ispassed, and this results in a voltage droppreventing oscillation at a certain point ;that a leaky condenser forms a similarloss, or, what is more probable, that theoscillator fails to function at a certaintemperature due to faulty windings on thecoils. However, it would be preferable tohave the set tested by a good serviceagent if you cannot approach the makersdirect.

Mains Breakdown" My three -valve A.C. set has broken

down and I am at a loss as to the cause.When I switch on there is a hum from thespeaker, not so loud as it used to be. All thevalves get hot, the rectifier unusually so.I only have a small two -range voltmeter, butwhen I put this to the terminals of theheaters on any valve in the set the needlevibrates. Is this A.C. ? When I put it fromearth to any of the H.T. positive points itjumps a very little bit but comes back to 0.Is it possible to make any suggestion tolocate the trouble?"-S. W. (Hampstead).

AS hum is heard from the speaker andthe needle of your meter vibrates

or quivers on all heater terminals, theindication may be regarded as acquittingthe heater winding on the transformer.The slight flick when the H.T. circuit ismeasured may be due to condenser dis-charges, but some indication should begiven of the approximate voltage even

with your cheap meter, and thefairure to obtain this, together withthe failure of signals would indicatean interrupted H.T. circuit. This

may be due to the transformer winding,the choke, the rectifying valve, or a by-pass condenser which has broken downand is short-circuiting the H.T. sup-ply. If the transformer winding failedthe rectifier would only receive the normalheater voltage supply and would not,therefore, get very hot. If the H.T. wasapplied to the valve and it was in order,but the choke had broken down, the valvewould still only rise to a temperatureslightly above normal. Similarly, if theH.T. negative return was interrupted noundue rise should be observed. Therefore,the fact that the rectifier gets unusuallyhot would indicate that it is being seriouslyoverrun, and as no H.T. can be detectedin the receiver the H.T. must be short-circuited in the mains unit. The smoothingcondensers should therefore be removedone at a time, when signals will be restored

ri.0410.1).MNMO041MINIIIIIP0411M1)01.0.1..,4111,41/10=1.04.2

I RULES!

i fact that the Queries Service is intended only iWe wish to draw the reader's attention to the1

for the solution of problems or difficultiesarising from the construction of receiversdescribed in our pages, from articles appearingin our pages, or, on general wireless matters. 1

We regret that we cannot, for obvious reasons-! (3) Supply circuit diagrams of complete I

multi -valve receivers.(2) Suggest alterations or modifications of I

ireceivers described in our contem-poraries.

i(3) Suggest alterations or modifications to

commercial receivers. 1

(5) Grant interviews to querists.(4) Answer queries over the telephone.

iIPlease note also, that queries must be limitedto two per reader, and all sketches and draw- Iings which are sent to us should bear the

1 name and address of the sender.If a postal reply is desired, a stamped addressed envelope

must be enclosed. Send your queries to the Editor,

1

PRACTICAL AND AMATEUR WIRELESS, GeorgeNewnes, Ltd., S-11, Southampton Street, Strand,

London, W.C.2.

41100.0.0.10410111,011111.11.1Milin.1104M1.1.10.0041141401

as soon as the defective condenser is re-moved, although hum will, of course, beexperienced. Alternatively, you can removethe condensers and test them in the usualway, although in the case of electrolytics itis rather difficult to locate an excessiveleakage of current which may cause abreakdown of the type mentioned in yourcase.

Making a Superhet" I am rather keen to build a superhet,

but as expense is an important point I wantto cut down to the very minimum the partsneeded. 'I have several odds and ends athome, but I should like a really efficientcircuit. What may be regarded as theminimum number of valves to build a super -


ENCYCLOPEDIABy F. J. CAMM II attihon

(Editor of Practical and AmateurWireless'') 'I net

Wireless Construction, Terms and Definitionsexplained and illustrated in concise, clear

language.From all Booksellers, or by post 516 from GeorgeNewnes, Ltd., 8-11, Southampton Street, Strand,

London, W.C.2.

het of the type I require ? Is your. £4 Superhet4 the best in this respect ? "-I. L. A.(Hampton).

THE minimum number .of valves toemploy the superhet feature is one,

and a circuit showing the arrangement wasgiven in our issue dated. February 8th last.We have also described a two and a three -valve superhet. None of these employedA.V.C., however, and as you are anxiousto build the most efficient type of circuityou may wish to include this feature. Inthat case three valves could be used, andthe first could be the frequency changerand mixer (using either a pentagrid ortriode -pentode or similar type of valve)and the intermediate -frequency stage couldutilise a pentode. You could then utiliseWestectors for 2nd detector and A.V.C.,followed by a pentode output valve, or adouble -diode -pentode for these three pur-poses.

Short-wave Damping" I have built a home -designed two -

valve short-wave set, in which I am usingcoils wound on comraereial coil formers.I find, however, that when I tune to 20metres I seem to have reached the 'lowerlimit of working on this set as nothing ofany kind can be heard below this, no matterwhat coil I plug in. The aerial is 20ft.,horizontal, seven -strand cable, thoroughlyinsulated, and the earth wire is 5ft. long,joined to a four -by -two sheet of coppergauze. I do not know how to improve this,but should like to get lower down the scale.Can you help me, please ? "-B. R. (Salis-bury).

THE trouble may be, due to the designof the tuning coils you are using. No

matter how efficient the aerial -earth system,the damping imposed on the grid coil mayeasily prevent the valve from oscillating.Even when a pre-set condenser is joined inseries this may not prove effective, and aloose -coupled aerial coil winding should beadopted. Even a single turn may proveeffective and will enable the valve to oscil-late and thus produce the desired result.Try different types of winding, arranged indifferent positions on your coil until youobtain the desired result, but generallyspeaking the coupling should be quiteloose.

Control Knobs" I have built your £4 Superhet and am

delighted with the performance, but notwith the appearance. The componentswhich were specified and which are mountedon the panel are all supplied with differentknobs, and in one ease I have a walnutcolour and in the others they are black.'Is it not possible to standardise these partsor can I get new knobs so as to make theset look neat from the panel ? "-D. G. F.(Perth).

is not possible to standardise control1 knobs as various people have differentideas as to the best type. However, yourdifficulty may be overcome quite easily, byobtaining replacement knobs from Messrs.Bulgin. If you obtain a copy of theircatalogue you will see reproductions oftwenty-eight different knobs and will nodoubt find a pattern which will suit yourparticular cabinet or other furnishings. Theknobs range from simple walnut roundmodels to black and chromium domedtypes.

The coupon on cover iii must beattached to every query.

MMINIMIN).

572 PRACTICAL AND AMATEUR WIRELESS August 15th, 1936.

Miscellaneous AdvertisementsAdvertisements are accepted for thesecolumns at the rate of 3d. per word. Wordsin black face and/or capitals are chargeddouble this rate (minimum charge 3/- perparagraph). Display lines are charged at6/- per line. All advertisements must beprepaid. All communications should beaddressed to the Advertisement Manager," Practical and. Amateur Wireless,"8, Southampton Street, Strand. London.

RECEIVERS, COMPONENTS ANDt" ACCESSORIES


RADIOIVIART (G5111)SHORT-WAVE SPECIALISTS



electrolytics 8 mf. 500, 2/11, 4 x 4 mf.. 1/0, 25 mf.,25 v., 1/-, etc.

RADIOMART. Smoothing chokes, 20 by 120 ma.,3/11 ; 100 ma., 2/11 ; 40 ins., 1/11. Telsen Ace

transformers, 1/11. Radiogrands, RG48, 2/9. BTHSpeaker, 2/11.

RADIOMART. Varley iron -cored, 10/6. Bifocaldual-range coils. Very selective, 2/11 ; matched

pair, 5/3.

RADIOMART.Pushback wire 6 yds. W., heavy

9d. ; 2 gross solder tags, 6d. Resincored solder,9ft., 6d.

RADIOMART,Centralab pots, all sizes, 1/0 ;

switched, 2/-. Tubular glass fuses, 2d.RADIOMART. Igranic midget jacks, 3d.. Milliam-

meters, 25 ma. upwards, 5/9 ; super 6/9.RADIOMART. Telsen H.F. chokes, 1/11 screened

1/11. Utility 1036 SL wavelength dials, 3/11.RADIOMART. Lissen 3 -gang superhet kit coils,

two I.F.'s ganged condenser, ditto Bandpass,ditto 2 -gang all wave, 10/- kit.

RADJOMART.Traders' monster bargain parcels,

value £4/10/0 for 10/- ; also 5/- parcels.ADIOMA1tT. Famous continental A.C. valves,R 4/6. American Dutton, etc. All types, 3/0.

Battery from 2/3.RADIOMART. Utility 8/6, microdise dials, 3/11.

Radiophone .00016 short-wave condensers, 3/6.Series gap twin, 3/9.

RAD1OMART. Ceramic all brass mierovariables,15 mmfd., 1/4. 40 inmfd., 1/7. 100 msnfd., 1/10.

Short-wave HFC., Od.RADIOMART. Orders 5/- post free. Oct our bar-

gain catalogues. General, lid. 'Short-wave, 114.44, Holloway Road, Birmingham. Tel.: MID 3254.


VAUXHALL. UTILITIES, 163a, Strand, W.C.2.Over Denny's the Booksellers. Temple Bar

9338.

CONVERSION UNITS for operating D.C. Receivers160 from A.C. Mains, improved type, 120 wattsoutput, at £2/10/0. Send for our comprehensive list ofspeakers, Resistances and other components.WARD, 40, Farringdon Street, London, E.C.4.

Telephone Holborn 9703.

ALL lines advertised last week still available.RADIO CLEARANCE, 63, High Holborn,

W.C.I. Tel. : Holborn 4631.


HULBERT for Quality Surplus Speakers. AllMusic Lovers should write for List of amazing

bargains. Prices from 8/6 brand new. Made by bestknown British maker.-Hulbert, 0, Conduit Street,


Brand new stock with six months' guarantee. 2 vo,tDetector, 2/3, Power 2/9, Screen Grid, Pentode, H.F.Pentode, 5/-. -The, following American typo valves,fully guaranteed, at 5/6 each: No. 80, 42, 43, 57,58, 77, 78, 6C6, 0D6, 25Y5, 25Z5. Write for otherprices to: Dulci Electrical Co., Ltd., 7, LizardStreet, London; E.C.1.

LOUDSPEAKER REPAIRS

REPAIRS to Moving Coil Speakers, Cones and Coilsfitted or rewound. Fields altered. Prices

Quoted including Eliminators, Loud -speakers Re-paired, 4/, L.F. and Speech Transformers, 4/- postFree. Trade invited. Guaranteed. Satisfaction.Prompt Service. Estimates Free. L. S, Repair Ser-vice, 5, Balham Grove, London, S.W.12. ' Battersea1321.



S.W.4. (Macaulay 2381)and 165 and 165a, Fleet St., E.C.4 (next toAndertons

Hotel). (Central 2833.)NOW READY ! Send 4d. in stamps for NEWILLUSTRATED GIANT CATALOGUE AND VALVE

LIST.

SHORT WAVES.S HORT-WAVE COILS 4 to 6 -pin types. 13-2G,

22-47, 41-94, 78-170 metres, 1/9 each withcircuit. Special set of 3 S.W. Coils, 14-150 metres,4/-, with circuit. Premier 3 -band S.W. Coil,11-25, 19.43, 38-86 metres. Simplifies S.W. re-ceiver construction, suitable any type circuit, 2/-.COIL FORMERS, In finest plastic materials,

11in. low -loss ribbed 4- or 6 -pin, 11- each.eONDENSERS, super ceramic S.L.F. .00016,I/ .0001, 2/9 each; double-spaced .000015,.000025, .00005, 3/- each. All brass with integralslow-motion .00015 tuning, 3/9; .00015 res,ctien,2/9.SHORT-WAVE KIT for 1 valve receiver or

adaptor, complete with chassis, 3 coils 14-150metres, condensers, circuit, and all parts, 12/6.VALVE GIVEN FREE.2 -VALVE S.W. KIT, complete with valves, 19/6.

2 -VALVE S.W. KIT, S.G. Det. and Pen., completew with valves, 40/-.skAND PASS KIT, 14/6 the lot. Lissen 3 -gang00 coil unit. Utility 3-gang condenser anddisc drive 4 valve -holders, chassis and blue -print.QUPERH ET KIT, 15/6 the lot. Telsen

Superhet Coils, I.F.'s, 3 -Gang Condenser,Disc Drive and chassis.SPEAKERS, K.B. 8" P.M.s 9/6, Goodman 7"

P.M.s, 9/6, Rola 7" P.M.s, 10/-.MAINS TRANSFORMERS. Premier wire -end

type with screened primaries.H.T.8 & 9 or H.T.10 with 4v. 4a. C.T. and 4v. la.C.T., 8/6.250-250v. 60 m.a., 4v. la., 4v. 2a. and 4v. 4a., allC.T., 8/6.350-350v. 120 m.a., 4v. la., 4v. 2a. and 4v. 4a.,all C.T., 10/6.500-500v. 150 m.a., 4v. 2-3a., 4v. 2-3a., 4v. 2-3a.,4v. 3-4a., all C.T., 19/6.Any of those transformers with engraved paneland N.P. terminals, 1/6 extra.AUTO TRANSFORMERS, step up or down,

60 watts, 7/6, 100 watts, 10/-.MAIRS VALVES, famous Europa 4v. A.C.,

types, 4/6 each. H.L., L., S.G., Var.-Mu-S.G., H.F.-Pens., Var.-Mu.-H.F. Pens, 1, 3,and 4 -watt A.C. directly -heated output Pentodes.Full -wave rectifiers, 250 v. 60 m.a. A.C./D.C.types, 20 -volt .18 amp. S.G., Var.-Mu-S.G., H.,H.L., and Power.Following Types all 5/6 each. Full -wave rectifiers359v. 120 m.a. and 600 v. 120 m.a. 21- watt in-directly -heated Pentodes. Frequency Changers.Octodes and Heptodes.D ATTERY VALVES. 2 -volts, H.F., L.F., 2/3.B

Power, Super -Power, 2/9. S.G., Var.-Mu-S.G., 4 or 5 -pin Pentodes, H.F. Pens., V.-Mu-H.F.Pens., 5/-. Class B, 3/6.AMERICAN VALVES. Genuine American

DUOTRON, all types, 3/6 each. Hytronsuper quality, 3 months' guarantee, all types, 6/6.RAI L LI AM M ET E RS, moving -iron flush 21",

all ranges from 0-10, 5/9. Visual tuning,6 or 12 m.a., 5/-. Moving coil meters, 21" 0-1 m.a.,18/6 ; 3r 0-1 m.a., 22/6. Multipliers, 1/- each.Westinghouse meter rectifiers, 17/6 each.E LECTROLYTICS. U.S.A. 4, 8 or 12 mfd. 520 v.

peak, 1/9 each. Dubilier, 4 or 8 mfd. 500 v.,3/- ; 50 mfd. 50 v., 1/9 ; 25 mfd. 25 v., 1/-. T.C.C.4 or 8 mfd. 050 v., 4/- ; 15 mfd. 50 or 100 v., 1/-;50 mfd. 12 v., 1/-.Paper Condensers. W.D., 250v. working 4 mfd.,2 mfd. 1/-, 1 mfd. 6d. ; 350 v. working 4 mfd. 2/6.2 mfd. 1/6, Dubilier 500 v. working 4 mfd. 4/-;800 v. 4 mfd. 6/- ; 2 mfd. 750 v. 3/-

.Wego 450 v. working 1 mfd. 1/-, 2 mfd. 1/9, 4 mfd.3/- ; 700 v. working 2 mfd. 2/-, 4 mfd. 3/6 ; 1,650 v.working 1 mfd. 3/6, 2 mfd. 5/6.TRANSFORMERS, latest type Telsen R.G.4

(list, 12/6), 2/9. Lissen Hypernik Q.P.P.(list, 12/6), 3/6.ELIMINATOR KITS for A.C. mains. 1.20 v.

20 m.a. )r 150 v. 25 m.a., 10/-, tappedS.G. det. and output. Complete Kit with long -lifevalve rectifier (replacement cost only 2/-).ftISSEN ALL -ELECTRIC A.C.4, S. Grid. Det.,

Pen. and Rectifier, M.C. Speaker. (List,£9.9.0.). Our price, 65/-.n.E.C. AC/DC ALL MAINS THREE. Our40 price, 75/-.Potentiometers by well-known makers. All valisesup to 1 meg., 2/- ; with switch, 2/6.

0RECEIVERS, COMPONENTS AND

ACCESSORIESSurplus, Clearance, or Secondhand, etc.

SOUTHERN RADIO'S WIRELESS BARGAINS.L.3 ALL GOODS GUARANTEED AND SENTPOST PAID.

SPEAKERS.-Celestion Soundex Permanent Magnet,10/-; Telsen Permanent Magnet with ten -ratio

transformer, 12/6; Blue Spot 99P.M. ExtensionSpeaker, 20/-; 45P.M. Extension Speaker, 17/6;Telsen Loud Speaker Unit, 2/6; all new and boxed.


quisite Bakelite cabinet with Osram M.C. Speaker.Ready to plug in to any mains. Fully guaranteed.New, in sealed cartons, £3/5 (list £7/15).

Colpact 3 -valve Battery Sets complete with3 Osram valves, moving coil P.M. Speaker in

attractive Bakelite cabinet, makers' 1936 series inoriginal sealed carton, 50/- (List £5/10/0).

MULLAKD M.B.3 three -valve battery sets. Com-plete with v, batteries, accumulator, M.C.

Speaker. Three Milliard Pentode valVes in beautifulwalnut cabinet. Brand new, in sealed cartons, £4110(List £8/8).

TELSEN A.C. D.C. MULTIMETERS (latest 1930type). -5 -range for every conceivable test for


W349, midget size, 4/-; type W478 (twin), 9/ -pair; type W477 (triple), 16/.; type W476 (triplesuperhet selector and oscillator), 16/- set. All GangedCoils are Mounted on Base with -switch. I.F. Trans-former Coils W482, 5/-; Telsen Dual Range Coil withvariable series condenser W76, 4/ -; Varley SquarePeak Coils BP5, 2/,

ELIMINATORS.-3tegentone (1936) Type. W5awith trickle charger, 37/6; Type WIa (less

trickle charger), 32/6.HOUSE TELEPHONES. A SPECIAL BARGAIN.

BRAND NEW ONE -HAND TELEPHONES.Complete on stand, with or without Automatic Dials.Cost £4 each to manufacture, 10/ -each.

MICROPHONES.-Ace (P.O.) Microphones, com-plete with transformer, perfect with any type

of receiver, 4/6.TRU-OH31 RESISTANCES. -1 Watt. Wire ends

colour coded and marked ; 36 assorted capacitieson card, 6/-.

AMERICAN VALVES.-A full range of valves forall American sets at 7/- each. Brand new,guaranteed.

SOUTHERN RADIO BRANCHES. -271/275, HighRoad, Willesden Green, N.W.10 ; 46, Lisle Street,

W.C.2. All mail orders to 323, Euston Rd., N.W.1.SOUTHERN RADIO, 323, Euston Rd., London,


MISCELLANEOUS

SHORT WAVE on a crystal set. Full buildinginstructions and crystal, 1/2 post paid.-Radiomail,Tanworth-in-Arden, Warwickshire.

ALCO ELIMINATORS & CHARGERS. 4 H.T. taps.120V/150V. 20/30 m.a. 18/-, with charger 25/-.

Charger alone 7/6. 1- amp. 11/-. Year's guarantee.Details free. P. & D. RADIO, 1, Goodinge Rd., N.7.

3S.EACH any popular type of 'American valves.

90 days guarantee. Orders 10/- or over CarriagePaid. Satisfaction or Money Refunded immediately.RADIOGRAPHIC LIMITED, 66, OSBORNESTREET, GLASGOW, CA.

IRELESS FOR THE MAN -IN -THE -MOON,"by Coulumbus and Decibel, 2s. 6d.' net.-

Writing about the book the "Midland Daily Tele-graph "says : " It is both good fun and sound theory."-At all Booksellers and Libraries, or from GeorgeNewnes, Ltd., 8-11, Southampton Street, Strand,London, W.C.2.

"THE OUTLINE OF WIRELESS," by Ralph1 Stranger. Fifth edition, 8s. 6d. net.-This

book, which covers the subject from A to Z,.,ia to berecommended to all who desire to master the thedryof Modern Wireless. At all Booksellers and News-agents.-George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2.

ADICTIONARY OF WIRELESS TERMS, byRalph Stranger. A Wireless Work of Reference

that should be on the bookshelf of every keen amateur.Compiled by a master of lucidity, it gives the meaningsof all Technical terms in general use. Price 2s, 6d.from all Booksellers and Newsagents.- George Newnes,Ltd., 8-11, Southampton Street,Strand, London, W.C.2.

FOR THE RADIO ENTHUSIAST-"The WirelessConstructor's Encyclopaedia," by F. J. Camm

(Editor of " Practical and Amateur Wireless "),third edition. Compiled by one of the most accom-plished designers and writers on the practical side ofWireless, it covers the whole field. A veritable Treasuryof Wireless Knowledge. Price 5s., from all Booksellersand Newsagents.-George Newnes, Ltd., 8-11, South-ampton Street, Strand, London, W.C.2.


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PARTS FOR ANY SET. ANY MAKE OF SPEAKER.New goods obtained for every order.

Send 21,8 a fist of parts or calves you require or any speakeryou may select and we will forward you a definite

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101 BARGAINSROME RECORDING-Amplifiers--Mikes, etc.

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This coupon is available until August 22,1030, and must be attached to all letters con- 1

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MISCELLANEOUS

FIFTY TESTED WIRELESS CIRCUITS, by F. J.Camm, 2s. 6d.-This handbook contains every

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PERPLEXITIESand TANTALISERS.-"The

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EVERYMAN'S WIRELESS BOOK, by F. J. Camm,3s. Od. net. An invaluable book of reference

explaining the operation, upkeep and overhaul of alltypes of wireless receiver. 200 illustrations. Fromall Booksellers and Newsagents.-George Newnes,Ltd., 8-11, Southampton Street, Strand, London,W.C.2.

TELEVISION.-NewnesTelevision and Short-

wave Handbook, by F, J, Camm, deals authori-tatively with Scanning Systems (Drums, MirrorScrews, Discs, etc.), Neon Lamps, The Cathode -RayOscillograph, How to Build Short-wave and Ultra -short -wave Receivers. Fully illustrated. Is. 6d. net.From your bookseller.-George Newncs, Ltd., 8-11,Southampton Street, Strand, London, W.C.2.

TM PRACTICAL MOTORIST'S ENCYCLOPZ-DIA, by F. J. Camm, 35. 6d. net. A lucid

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& Son, Ltd., 120 pages of fully coloured contour mapsfor the whole of England, Scotland, Ireland andChannel Islands, with Index to the principal Motoringand Cycling centres and distances, 2s. lid. from allBooksellers.-George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2.-

VISITORS TO LONDON should get Newnes HandyPocket Atlas and Street Guide to London. Edited

by John Bartholomew & Son, Ltd., 18 coloured Maps,General Index to Streets and Railway Stations. 2s.

from all booksellers.-George Newnes, Ltd., 8.11,Southampton Street, Strand, London, W.C.2.

"WORKING MODELS and How to Make Them."

Edited by F. J. Camm, Is. 6d.-This Bookwill appeal to all who are handy with tools. Containscomplete instructions for the making of every kind ofworking model. Each model has been actually con-structed in accordance with the details given andsubjected to stringent tests. The instructions anddiagrams are so clear that even the most elaboratemodel can be built without fear of failure. Obtainableat all Booksellers and Newsagents.-Geo. Newnes,Ltd., 8-11, Southampton Street, Strand, London,W.C.2.

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iv PRACTICAL AND AMATEUR WIRELESS, August 15th, 1936

MODERN MOTOR REPAIRAND OVERHAULING

A Practical Work on Motor.Car Maintenance and Repair.

Compiled by Practical Men for the Use of theMechanic, Garage Proprietor and Motor Owner

1, 5 6 8 Pages2,500 Illustrations

3 ChartsIn four Volumes, strongly boundin Cloth, lettered 2z -carat gold.

4,30Eati hODEOS

MOTOR MOTOR

%EWA itSPAtitaborotr.:3 entottadk

Why this Work willInterest YOU

i. Because experienced men inthe Garage Industry consider it tobe the best book of its kind yetpublished.

2. Because it contains no frills andno padding. The language is straight-forward and clear. The articlestell you exactly how to start anyparticular job, how to proceed andhow to finish in a workmanlikemanner.

3. Because the information issound and authoritative, havingbeen supplied by men who havemany years' experience in motorrepair work.

4. Because it places the advice of35 experts at your service.

5. Because whether you wish toreline the clutch of an Austin" Twelve -Six," to rewind the arma-ture of a burnt -out starting -motor,or to overhaul an A.E.C. Ignition-Compression engine, you will find inthis work just the information yourequire to enable you to do the jobin the shortest possible time con-sistent with good and reliable work-manship.

6. Because to the motor mechanic" MODERN MOTOR REPAIR"is worth many times its cost.

Use Coupon below for FREE illustrated descriptive Brochure. It will be, arevelation to you. By writing you place yourself under no obligation.

To THE HOME LIBRARY BOOK CO.,, George Newnes, Ltd.,

8-11, Southampton Street, Strand, London, W.C.2Please send me FREE copy of your illustrated Brochure giving full particularsof " MODERN MOTOR REPAIR." This places me under no obligationwhatever.

Address

P.W. 15836. if yoq do not erish to cut your copy, r fl a postcard mention " Practiral If iralexs" to address above.

Published every Wednesday b:* GEORGE NEWNES, LIMITED, 8-11, Southampton Street, Grand, London, W.C.2, and Printed In Great Britain by TEE NEWNES &PEARSON PRINTING CO., LTD., Exmoor Street, London, W.10. Sole Agents for Austral.. and New Zealand : GORDON & GOTOH, LTD. South Africa : CENTRALNEWS AGENCY, LTD, Practical and Amateur Wireless can be sent to any part of the World, post free, for 17s. 8d. per annum; six months, 8s. 104Registered at the General Post Office as a newspaper and for the Canadian Magazine Post.

Practical and Amateur Wireleje, Auo.st 22nd, 1936.

ORDER NEXT WEEK'S SHOW NUMBER NOW !

"GEORGEN EWNESPat/calla/

Vol. 8. No. 205.August 22nd, 1933.

Riiiedey F. J . CAM M

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EXHIBITION

"HOME PORTRAITURE with the MINIATURE CAMERA"

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3/6 net or 3/0 post free from Book Dept.. GEORGE NETVNES, LIMITED, 8.11, Southampton Street, Strand, London, W.C.2. Out.ADvT.

PRACTICAL AND AMATEUR WIRELESS August 22nd, 1936

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There are those who think that to paint the garden gate all one has to do isto buy a pot of paint and a brush. Only when they try do they find out how muchmore there is to it.

Disasters that have befallen the unwary white -washing ceilings would filltwo volumes of Punch.

But there is no reason why one should not save time and money and developa fascinating hobby in home decorating and painting with the help of this modernand practical little volume. Each section has been carefully thought out andarranged by an expert, from the initial choice of colours to the mixing of thepaints, from the buying of the brushes and other materials to the final application.It is expounded in the simplest and most detailed language, so that the merestnovice should produce a workmanlike job.

The illustrations are not mere decorations, but an essential amplification ofthe instructions of the text.- The book is the most comprehensive on the subjectat the modest price of Is. and is a triumph of compact compilation. Each para-graph and section is clearly " indexed ' for quick and easy reference. It isonly one of the famous Newnes' Home Mechanic books.

Here are some others in theseriesTHE HOME WOODWORKERMODEL BOAT BUILDINGTHE HANDYMAN'S

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August 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 573

NEXT WEEK: COMPLETE GUIDE TO THE SHOW.

r a i aTechnical Staff:

W. J. Delaney, H. J. Berton Chapple, Wh.$ch.,B.Sc., A.M.I.E.E., Frank Preston.

VOL: VW. Ito. 205, August 22nd, 1936.

ROUND the WORLD of WIRELESSTelevision Sound Transmissions

HAVE you heard the television soundbroadcasts yet ? These may be

heard at odd times during the day on awavelength of 7.23 metres, various musicaland speech items being used. Although asyet only experimental, it will be found thatthe musical quality is distinctly differentfrom the normal broadcast items. When asimple straight circuit is employed the itemswill appear more brilliant, but if a reallywell -designed " quality " circuit is usedthese items take on a completely differentair. At the time of writing no vision trans-missions have been picked up.

Belfast Radio ShowTHE date of the Belfast Radio Show has

now been fixed, and it will be held atthe Plaza, Chichester Street, Belfast, fromSeptember 9th to 16th inclusive. In viewof this new selection of dates the exhibitionwill overlap the Dublin Radio Show.

All -language News BulletinsWHAT station holds the record for the

largest number of languages usedfor its news broadcasts ? The Belgradeshort-wave station, on 49.17 metres,probably heads the list as it broadcasts anews bulletin in French, Italian, German,Turkish, Greek, Magyar and Albanian, aswell as in English. The station closes downat midnight with good -night greetings inpractically every tongue.

Television in S. AfricaTHE forthcoming Johannesburg Empire

Exhibition will feature television; forwhich purpose a private order has beenplaced in this country for the supply of atransmitter and five receivers. A standardof 90 lines will be used and a picture size8in. by 7in. In addition to a demonstrationof modern television broadcasts, visitorsto the show will be able to have their facestelevised and viewed in another part of theexhibition by their friends. .

B.B.C. Empire TransmissionsMR. HOWARD ROSE has been

appointed Empire Production Direc-tor, and it is proposed to improve the short-wave transmissions for Empire listeners.The Government has not authorised the useof foreign languages in B.B.C. broadcasts,and, therefore, the standard of Empirebroadcasts is to be raised. Mr. Rose is thesenior dramatic producer at the B.B.C.,

and has produced at least 600 radio plays,including " Dr. Abernethy," " The Schoolfor Scandal " and " Bulldog Drummond."

NEXT WEEKFully illustrated

Guide to theRadio Show

ORDER YOURCOPY NOW !

OUR STAND No. 10,GROUND FLOOR

From the U.S.A.ANOTHER unusual application of radio

comes to hand from U.S.A., this timein connection with the death of an Americancitizen who wishes to safeguard himselfagainst burial alive. He had ordered thata microphone be installed in the coffin,connected to an amplifier and loudspeakerinstalled in the cemetery guardian's house.

Editorial and Achiertisement Offices :" Practical and Amateur Wireless," GeorgeNewnes, Ltd., 8-11, Southampton Street, Strand, i

W.C.2.'Phone : Temple Bar 4363.

Telegrams : Wireless, Newnes, Rand, London. ,

; Registered at the G.P.O. as a newspaper and for Itransmission by Canadian Magazine Post.

The Editor will be pleased to consider articles ofi a practical nature suitable for publication in

PRACTICAL AND AMATEUR WIRELESS. Such Iarticles should be written on one side of the paper

; only, and should contain the name and address of 1'the sender. Whilst the Editor does not hold himselfresponsible for manuscripts, every effort will bemade to return them if a stamped and addressedenvelope is enclosed. All correspondence intendedfor the Editor should be addressed : The Editor,PRACTICAL AND AMATEUR WIRELESS, Geo. Newnes,Ltd., 8-11, Southampton Street, Strand. W.C.2. ;

Owing to the rapid progress in the design of ;; wireless apparatus and to our efforts to keep our

readers in touch with the latest developments, we It give no warranty that apparatus described in our

columns is not the subject of letters patent.

The apparatus is to be supplied with powercontinuously for a year so that should herevive he can immediately call for assistance.To test the apparatus during the year asmall bell is to be installed in the coffin.

Radio on the Coffee PlantationsIN certain colonies where large plantations

are cultivated, such as the coffee plan-tations in Kenya, etc., telephones, andsometimes primitive native signals havebeen used for communications between theoverseer and head office or between variousworking parties on the plantation. Portableshort-wave transmitters and receivers arenow being employed for this purpose, how-ever, and more reliable working andreduced costs are claimed to be effected bythis modern method of communication.

S.W. Equipment for FinlandTHE Public Schools Expedition to Fin-

land is being equipped with somespecial short-wave gear made by the Short -Wave Radio Society of Cambridge with theassistance of Pye Radio. The equipmentincludes six two -valve battery receivers,each weighing 1911bs. with batteries. Thewavebands covered are 20, 40, 80 and 600metres, and the expedition will keep intouch with the Admiralty on 8,630 kc/s.The transmitters are of the crystal -con-trolled type for telegraphy only and aredesigned for the 20, 40 and 80 -metres bands.The call -sign of the Short -Wave Society'sstation is G5JO.

Indian BroadcastingAS we go to press it is announced that

Mr. C. W. Goyder has been appointedEngineer -in -Charge of All -India radio.Experimenters will remember that Mr.C. W. Goyder was the first amateur tohold two-way radio conversations betweenEngland and New Zealand, and he followedthis feat by several other short-waveachievements, and all whilst he was stillattending school.

All -Wave SetsIT is interesting to note, after our recent

comment regarding the short-waveranges covered. by " all -wave " receivers,that at Radiolympia for the first time thistype of receiver will be on view coveringthe short-wave ranges down to 7 metres.These are H.M.V. products, and are thefirst British or American all -wave receiversto cover such a low wave -range.

574 PRACTICAL AND AMATEUR WIRELESS August 22nd, 1936

THE PICK of the PROGRAMMESB.B.C. Midland Orchestra

THE guest conductor for the concert onAugust 21st is to be Anthony Bernard,

who is music director at the Stratford-upon-Avon Memorial Theatre. He is in chargeof the music during the ShakespeareFestival there, and broadcast in the recentproduction of " MuchAdo About Nothing,"for which he wrotethe incidental music.

Concert from Tor-quayWALTER

GLYNNE(tenor) will be thevocalist at the Concertby the TorquayMunicipal Orchestra,conducted by ErnestW. Goss, to be broad-cast from The Pavilion,Torquay, on August25th.

A TangoProgramme

HARRY ENGLE-MAN'S QUIN-

TET have with" -themSchofield Earl (pianoaccordion) for t hetango programme fromthe Midland Regionalon August 24th. HarryEngleman is the sonof Joseph Engleman,the composer.

Florence Oldham


;11,41=11.411!114111114 1.mmIN10.1).N.

A Pianoforte TrioTHE Stephen Wearing Piano Trio is to

broadcast Schubert's "Trio in BRADIO IN THE KITCHEN

4esetr...;...sesesseaussa...Cookery talks on the radio are invaluable to the modern housewife. Here is the new McMichael light-

weight portable all handy for the morning's work.

The Elite Dance BandTHE St. George's Hotel Elite Dance

Band, led by. T. W. Robinson, willgive a short- programme of dance musicfrom the St. George's Hotel, Llandudno, onAugust 28th. The Elite Band are the pre-sent holders of the North Wales Dance

Band Chtmpionship.

" Up North ThisWeek "DOROTHY STAN -

TON, the well-known soprano, , isreturning to her nativeNewcastle on August26th when, as an " UpNorth this Week "artist, she will broad-cast a recital froth thelocal studios. MissStanton was a pianistbefore she took upsinging ; in the lattercapacity she made herdebut with Sir Hamil-ton Harty and theHalle Orchestra.

MISS OLDHAM has been a Midlandradio favourite since the early days

of broadcasting. She is to give a fifteen -minute programme of songs at the pianoon August 25th.

Autumn Dance Band ProgrammesGERALDO and his Orchestra will be

heard in a new type of programmeevery other week starting in the week ofOctober, 5th.

Jack Payne with his Band will broadcaston September 29th, and on October 1, 2,8 and 9.

Once a week for thirteen weeks fromSeptember 28th, Van Phillips will bring aspecial orchestra of picked musicians tothe studio for a programme lasting half anhour.

With the title " Evergreens of Jazz,"George Scott -Wood and his Orchestra willpresent three programmes, the first onAugust 25th, the second on September 10th,and the third in the week of September 20th.

Carroll Gibbons and his Orchestra willbroadcast every other week from the weekcommencing October 5th, and Peter Yorkeand his Band will be heard on November18, 20 and 21.

Arctic Explorer's TalkON August 21st, in the Midland Regional

programme, A. W. Moore, of Lough-borough, who was in the Oxford UniversityArctic Expedition with Edward Shackleton,will give a talk in the " Seeing Life " serieson a winter spent in the far North. He hasalso had experience of tropical exploring,for he was a member of an expedition toSarawak, Borneo.

flat " from a Manchester studio on August23rd. The Trio consists of Stephen Wearing(piano), of Liverpool, Leonard Hirsch(violin), of Manchester, and Haydn Roger-son ('cello), also of Manchester. Messrs.Hirsch and Rogerson are both prominentmembers of the Halle Orchestra ; Mr.Hirsch is also the leader of the well-knownHirsch Quartet, of which Mr. Rogersonwas formerly a member. The Trio is not anew combination, but it has never broadcastbefore.

& Entertainment from PaigntonL

THE ADELPHI REVELS, presented byGeorge Hay and Gordon Lane, will

broadcast from the Adelphi Gardens,Paignton, on August 25th.

Military Band ConcertAMONG the bands which have engage-

ments at the Jephson Gardens,Leamington Spa, is that of the 9th Queen'sRoyal Lancers. A. J. F. Allen will conducta popular programme on August 27th,closing with the Regimental Slow March" Men of Harlech "-adopted because theregiment was raised in 1715 by GeneralOwen Wynne, who was Welsh.

Concert Party from TroonANOTHER excerpt from Harry Kemp's

Show will be broadcast from theConcert Hall, Troon, on August 27th. Theartists will include Pete Martin and CharlieHolbein ; Ina Harris ; Donald Reid ; AlexFinlay and Rita Andree ; Jack Rowlands ;Wilson, Rogers and Taylor ; and LouisFreeman's Band, conductor, Jack Ansell.The production is by Julian Rose.

Summer Revue fromNewquay

"WHITE NOTES,"

a SummerRevue presented bySimrose and Watney,will be broadcast fromthe Summer Theatre,Newquay, on August20th. The guest artistof the evening will beRenara.

Gilbert and Sullivan ConcertCONDUCTED by Alfred Barker, the

B.B.C. Northern Orchestra will broad-cast a Gilbert and Sullivan concert onAugust 21st. The programme will includeselections from " The Mikado," " Patience "and " The Pirates of Penzance." AlfredBarker is normally the leader of thisorchestra.

STORE THIS°PROBLEM No. 205.

Bowen bought a kit of parts for a mainsthree -valve receiver, but after wiring had beencommenced -he found that the heater windingsof his mains transformer were not providedwith centre taps. What was the easiestmethod of providing the required centre taps ?Three books will be awarded for the first threecorrect solutions opened. Address your lettersto the Editor, PRACTICAL AND AMATEUR WIRE-LESS, Geo. Newnes, Ltd., 8-11, SouthamptonSt., Strand, London, W.C.2. Envelopes mustbe marked Problem No. 205 in the bottomleft-hand corner, and must be posted to reachthis once not later than the first post Monday,August 24th, 1936.

Solution to Problem No. 204.Cousens should have obtained a fixed resistance of

approximately 30,000 ohms and a variable potentio-meter of approximately 50,000 ohms. One end of thefixed resistance should be connected to the H.T. 120/150terminal of the eliminator, the other end to one of theend terminals of the potentiometer, the other endterminal of the latter to H.T.- of the eliminator, andthe centre terminal to the screening grid lead of theS.G. valve.

The following three readers successfully solvedProblem No. 203, and books are accordingly beingforwarded to them : G. Weldon, Hillside, Upper EastHayes, Bath ; J. W. Wilson, 36, Cardiff St., Man-chester 9; A. L. Aylmer, Croy House, Croy, Ayrshire.


ADVANCE SHOW

4 new note in cabinet design. The ivory andblack Ekco model.

AN analysis of the information so farreceived from the various exhibitorsat Olympia this year shows that

there is to be a. marked increase in thedevelopment of short-wave apparatus.This is due partly to the forthcomingtelevision transmissions (which are to becarried out in the ultra -short wavelengths)and also to the increased entertainmentwhich listeners are finding on the short-wave bands. Here, in addition to the enjoy-ment afforded by the actual broadcasts,

An aerial system designed to avoid man-madestatic-the Belling -Lee Eliminoise Aerial Kit.

there is the added pleasure of stationhunting, and until one has tried out ashort-wave receiver, one does not realisethe thrill which is experienced when a long-distance short-wave station is logged. True,

!,,,,,.,,,DF,TAILSSome Notes of Interest Regarding a Few of the Exhibits which will

be Seen at Radiolympia, which Opens Next Week.

many of the stations fadeinterfered with by localference, but there are nowfor overcoming these defect

In the latter connection,year at Olym-pia severalnoise -freeaerial equip-ment a, de-veloped b yvarious firmsbut all havingin common thesame aim andmethod ofdevelopment.In certaindistricts trol-ley buses,

electric signs,and otherequipment isfound withina short dis-tance of thelisteners' aer-ial, and conse-quently thisgives rise tointerference. On the ordinary broadcastwaveband the trouble is not always suffici-ently bad to warrant the attempt at itselimination. On the short -waves, however,it will be found that many signals are un-readable unless some form of interference -eliminating device is fitted, and one simplescheme is to erect the aerial right away fromthe source of interference. This wouldobviously lead to an excessive length ofleading -in cable and would thereby give riseto losses. The trouble is overcome by utilis-ing a special matching transformer attachedto the aerial, with a similar componentattached to the wireless receiver, and thetwo linked together by a length of specialscreened cable. One such aerial system isillustrated in the first column on this page.and is a Belling -Lee product. Messrs. Wardand Goldstone, B.T.S., and many other firmswill be showing a similar arrangement, L.with their own development of the trans- '

former, the screened lead or both.

Gramophone Attach-mentsAnother aspect 'of 'radio

entertainment which is prov-ing of increased popularityis gramophone record repro-duction, but there are still anumber of receivers in usein which no provision hasbeen made for the use of thopick-up. Even when amodern table -model radio setis in use the pick-up may beattached, but there is noconvenient method of arrang-ing the actual turntable andpick-un. Many listeners will

The Vidor Port-able, whichpossesses someinteresting fea-

tures.

severely, or areelectrical inter -various schemess.we shall see this

construct their own gramophone motor -board, but the apparatus may be builtup in a more tidy manner if one of thespecial " add-on " turntable units is em-ployed. A well-known unit of this type,

For the measurement of capacities this new Avo Capacity Meter will be foundideal.

which has now been on the market for someconsiderable time, but which will, appearthis year in a new design, is shown on thenext page, and is the well-known Cosmo-cord Unigram Playing Desk, Model 84.This may be obtained in a figured walnutcabinet and a powerful induction -motor isfitted, together with the latest type Cosmo-cord pick-up, volume control and speed

(Continued on next page)

576 PRACTICAL AND AMATEUR- WIRELESS August- 22nd, 1936

ADVANCE SHOW. DETAILS(Continued from previous page)

regulator. It is obviously only suitable foruse on A.C. mains (50 cycles), and theprice is 4 guineas.

Double SpeakersLast year we saw some attempts at

improving reproduction by the fitting oftwo or more speakers, and the R.G.D. wasthe most ambitious of these receivers,utilising in the larger models three separatespeakers. ' This year the H.M.V. companywill be showing an entirely new design ofcabinet, in the Model 801 auto -radiogramin which three of the new elliptical speakersare 'employed. Amongst other firms whoare utilising multi -loud -speaker reproducer

A Portable Auto -radiogram in a real leather case.This is a product of the Self -changing Gramophone

Company.

are Burndept, and their Model 201 is shownat the foot of this page. This has twinspeakers arranged to direct the sound at anangle from each side and provides, inaddition to a high quality of reproduction,a neat appearance in the cabinet. A specialstool is provided for this particular re-ceiver and enables it to take its place inthe home in a neat and orderly manner.Cabinet Design

In the range of cabinet designs we shallsee some more startling changes from cus-tomary practice, the H.M.V. receiversprobably providing the most interestingexamples. One particular model wasshown in our issue last week, and, inaddition to this, they will be exhibiting areceiver designed on the lines of a writingbureau, and the method of curving the" silk " covering for the loud -speakeropening presents an entirely new note andlends to the complete apparatus a muchmore tasteful aspect. It is very pleasing tonotice this complete departure from the" fretwork and silk " which so oftenadorns the loud -speaker opening, and thenew material used by H.M.V. adds itsquota in improving reproduction. In theEkco designs the receivers are now followinga new design, although bakelite is stillgmployed in place of the customarytimber. On page 575 the latest black andivory model is shown and it is noted thatthis design is the work of Serge Chermayeff.The importance of the tuning scale, withoutdetracting from the appearance of thecabinet, is very noticeable in this particularmodel, and practically the entire top of thecabinet, is occupied by the scale.

The other Ekco cabinet at the top of thispage is designed to provide very high-

class reproduction.and it will be noted t4atthe sides of the cabinet are cut. away andprovided with gauze, whilst the loud-speaker is of the wide -range exponentialtype, claimed to provide an extendedfrequency range of 30 to 10,000 cycles,with level response from 50 to 8,000 cycles.This model is a nine -stage superhet with allrefinements, such as tone -compensatedvolume control, etc., and costs 22 gns.

Measuring InstrumentsMuch more space will be devoted this

year, too, to measuring instruments of alltypes, and every, constructor and serviceengineer will find this side of the hobby ofabsorbing interest. A new capacity meteris to be shown by the makers of the popularAvo range of instruments, and this par-ticular model is shown on page 575. Thisinstrument measures all capacities from 0to .1 mfds. in six separate steps, the actualcapacity being shown on the scale in thebottom right-hand corner of the instru-ment. No external standards are required,and the accuracy is of a very high order.The only additional power required for themeasurements is a 45-60 volt H.T. batteryand a 2 -volt accumulator.

Weston Electrical Instruments will in-clude a new output meter having A.C.voltage ranges of 2, 10 and 50, and a self-contained condenser for output measure-ments. The price of this component is£5 15s.

PortablesPortable receivers this year are stilt

smaller and the Burndept is a remarkably

The new Cosmocord Playing Desk, Model 84.

good illustration of the compactness whichmay be obtained in an instrument of thisnature. Some of the principal new features

For better reproduction. This Ekco cabinetcontains an exponential loudspeaker, giving very

realistic results.

in this section of receiver design are theincorporation of new Midget componentsand valves, and the cutting away of thelid of the containing case in order to permitthe sound to issue from both sides and thusavoid " boxiness " and to enable the pro-gramme to be heard when the recsiver isclosed up. A portable radio -gramophoneon new lines will be shown by Self -changingGramophones, Ltd., and on this page is areproduction of it. The case is of 'realleather, and an automatic record changer,playing from 1 to 8 10in. records with rejects at will, is incorporated. The price is28 guineas for the Universal mains model(190-250 volts) and 29 guineas for the D.C.model (190-250 volts). A separate double -pole mains switch is fitted to this particularinstrument so that it is rendered completely" dead " no matter to what type of mainssupply it is connected.

An interesting novelty is incorporated inthe Lissen portable, where the loudspeakeris mounted in a separate section of thecabinet (which is of the standard " suit-case " type), and this separate section isconnected to the lid by means of metalarms. When the lid is raised the speaker isbrought into a semi -raised position and thesound is thus directed in a more convenientmanner towards the listener. This methodof construction enables the case to be madeneater, as the lid then only contains theframe aerial.

At least one transportable will be onview, and this takes the form of a standardconsole model, fitted with a substantialcarrying strap so that it may be con-veniently carried from one room to another.It is not, of course, intended for use in theopen air in the same manner as a portable.

Messrs. Burndept have produced this model, in which twa loakeakers are incorporated.

August 22ncl, 1936 PRACTICAL AND AMATEUR WIRELESS

GAIN CONTROL577

In this Article the Various Kinds of Gain Control and Their Application are Dealt With. By C. V. COLLE

IN a recent article in this journal thewriter made a' -statement to the effectthat a " gain " control was one which

allowed for bas -frequency compensation,and the information given might lead oneincorrectly to assume that gain control hasapplication only to L.F. circuits. Whereasits chief use is in audio -frequency (A.F.)amplifiers, it is, nevertheless, employed inR.F. and I.F. systems, although to a smallerextent.

To avoid ambiguity, let us analyse theword " gain." A literal translation wouldbe "to increase " or " to add." In thestrictest sense of the word, therefore, a

gain " control could easily be called" volume " control !

Those receivers which incorporate a gaincontrol invariably include a volume controlof some description, hence, unless the formerfinds duplication in the latter, which is mostunlikely, the gain adjustment can be con-sidered to fulfil a different function of whichwe, are as yet unaware.

Before we proceed to analyse the varioustypes it would be as well to explain thatsome considerable looseness exists in thenaming of gain controls. The Americansappear to. be both the originators andviolaters of the terms, although some slightjustification would appear to exist fornaming a control " gain in sets in whichthe term does not strictly apply, but whichcannot be confused with a similar device inthe same receiver.

Various Types of ControlAn " I.F. gain " control has application

to a superhet, and obviously covers theintermediate -frequency gain or amplifica-tion. It is equally obvious that this controlis manually operated. In early superhets,and long before the word " gain " wasapplied to radio -set adjustments, theamplification of the I.F. valves was con-trolled by means of a wire -wound poten-

/-/T1-225vFOR AN Exisr/NG TUNER

ANODE OF TkODE DE rOR D.D.TRJODE

24.1FD.inifo

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000 OHMS

tiometer connected across the H.T. supply,the slider feeding the screen -grid circuits.

For numerous technical reasons whichneed to be enlarged upon here, control ofthe screen -grid voltage was rejected infavour of variable grid -bias. No doubt theadoption of variable -mu H.F. screen -gridand pentode valves was responsible for thechange, but the fact remains that thesevalves cover present-day practice. Forthe most part I.F. valves are now controlledautomatically with a grid -biasing voltagewhich is generated at the second detectorand which varies with the carrier -wavestrength of the received transmission.

Superficially, the use of an I.F. gaincontrol would seem to be a retrograde step,in as much as the idea of A.V.C. was to dis-pense with unnecessary knobs. Actuallythe I.F. manual -gain control is, in those setsin which it is fitted, augmented by theusual A.V.C. action, one or the other beingemployed by the movement of a switch.Even so, these refinements will not be foundin inexpensive sets, but in the more am-bitious all -wave outfits, such as large radio-grams and professional receivers in theRothermel-Hammarlund " Super -Pro "category.

Manual ControlReverting to the action of the manual

I.F. gain control, it is feasible that readersof an inquiring turn of mind will want toknow why it cannot be classed as a volumecontrol in view of its action in adjusting theI.F. valve amplification. The explanationis that as the second detector, usually adiode, is arranged to have a limited action,rotating the I.F. gain control to maximumwill not allow the volume to increasebeyond a defined limit. There is, of course,the possibility of the I.F. valves becomingunstable due to excessive amplification,but ruling out that effect, there must bea recognised high second -detector input,

0.s.

which will be just or slightly more thansufficient to load the output valves when thetrue L.F. volume control is at " maximum."

Justification for the manual control canbe discovered in the tendency for thesensitivity of the signal -tuned circuits andvalves to drop on the ultra -short wave-bands. The gain control allows the lastounce to be extracted from the valves(within the limits of stability), not only tomake up for the loss of sensitivity due tothe fall in amplification, but to receiveany weak transmission above the prevailingnoise level.

Gain Control in a SuperhetA similar R.F. (radio - frequency) gain

control as an alternative to an A.V.C.action (on a superhet the switch men-tioned above would control the I.F. stagessimultaneously) in the signal tuned circuitsallows the operator to demonstrate in con-vincing fashion the advantages of a highsignal-to-noise ratio. In other words, it isa desirable feature in a .superhet to providea good measure of amplification before thefirst detector, so that the following I.F. andL.F. stages may not be called upon to work" all out " and thereby create a noisybackground due to valve hiss. VariableR.F. and I.F. controls provide that flexi-bility of adjustment by which, at all times,the background noises may be reduced toa minimum consistent with the desiredprogramme volume, especially from weaktransmissions.

In the hands of a beginner the additionof these controls is apt to defeat theirpurpose. There is no reason, on the otherhand, why one experienced member of thehousehold should be' debarred from theirdefinite advantages provided A.V.C. isfitted as an alternative, and the extracontrols relegated to a part of the set whichis close at hand.

(Continued on next page)

5MFO.L.S.

FIELD7.500

1

ONN15 5A1F0

c),

04v/

104

200V

20 V

20v

Fig. 1.-A fixed form of L.F. gain contra! as used in a super -quality 14 -watt amplifier. The gain control is shown at "b" and a tone correctionresistance -condenser system at " a."

578

(Continued from previous page)

Whether gain control for the R.F. andI.F. valves is justified in a superhet cover-ing medium and long wavelengths onlydepends on the action of the 2nd detector.The usual action of this valve when generat-ing 'A.V.C. voltages is to limit thesensitivity so that only signals above acertain level are accepted. Should thecircuit arrangement be such, however, thaton the absence of a carrier -wave the sensi-tivity rises to the possible maximum, thengain control will offer no real advantages.There is, of course, always the possibilityof gain controls under these latter con-ditions providing a slightly better balanceof R.F. to I.F. amplification than ispossible with A.V.C.

As previously explained, the description" A.F. gain " control has no logical placein our technical dictionary. An " audio -frequency " gain control is an L.F. volumecontrol or merely a plain. " volume "control where no other exists on any singlereceiving -set. The word " gain " as appliedto the low -frequency amplifier in thiscountry usually applies to a method ofincreasing the bass response. Where pro-vision is made for increasing high notes inaddition to low, and by separate controls,such knobs would be labelled " gain con-trols," " bass " and " treble," or even" tone " controls.

Unlike tone controls, those of the L.F." gain '2 type are not intended to reduce highnotes so as to emphasige bans, or vice -versa. Their chief function is to raise bassor treble, and to do this without directlyaffecting the remainder of the soundspectrum. The scope of " L.F. gain " canbe increased by arranging the bass andtreble knobs to reduce as well as increase,although here again the effect is not quitethe same as with most tone controls.

L.F. AmplificationIf full provision is to be made for all

forms of L.F. gain, it is highly desirablethat ample L.F. amplification is provided.That is to say, the overall magnification

PRACTICAL AND AMATEUR WIRELESS August 22nd, 1936

should be considerably greater than re-quired, in order to provide a source or

sink " into which the A.G. signal impulsescan be poured, filtered and finally passedout suitably " dressed." One of the valvesearly in the L.F. chain will inevitably bemade a passenger, giving little amplification,or, alternatively, sufficient to be diverted.for the purpose of frequency correction.

bterli

h{Fae 467,47 .

.44/PL/AZER

/Fri

Osc se2E7

tone control is that it is difficult to gaugethe setting where the frequency spectrumis level. Few listeners are really com-petent to judge " balance," and clearlydefined " level" points on the gain controlknobs rule out errors of balance on thosetransmissions whichdonot require correction.

If these facts are borne in mind, there isno technical reason why set constructors

/F-72

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lb 7;w-rec.

Fig. 2.-One method of manually controlling R.F. and I.F. stages with the alternative of A. V.C. AD.C. source for gain control as shown can be obtained from a tapping in the H.T. supply, from a

separate rectified voltage source (giving only about 10mA) or from a battery.

A desirable feature is that those gaincontrols taking care of the L.F. responseas mentioned should be clearly marked bymeans of scales and pointers. It is par-ticularly essential that the " level " re-sponse is indicated, that is, where thecircuit constants provide a uniform fre-quency curve.

One of the disadvantages of the usual

should not indulge their ideas as to modify-ing the L.F. amplifier characteristics, toprovide, say, for high -note losses in thetuned circuits, and imperfection in theloudspeaker response. Should none ofthe modified circuit constants prove satis-factory, it is then an easy matter to revertto the standard arrangement merely byturning the L.F. gain switch or switches.

" Musical Mixture"MERVYN SAUN-

DERS (tenor),Norma Dursley (banjo)and the BristolAccordion Club Band I

_AN.

conducted by PercyC. Sullivan will broadcast in the secondnumber of the series " Musical Mixture "on August 29th,i.n the Western programme.

PROGRAMME NOTES

Recital from Cheltenham CollegeMARIE HALL, the famous violinist,

and Philip Taylor, the CheltenhamOrganist and Director of Music at Chelten-ham College, are to give a recital from Chel-tenham College on. August 27th.

New Farce by John DightonJOHN DIGHTON, whose blandly in -J consequent burlesques of " LimehouseNights," " Raffles " and " The ScarletPimpernel" proved so popular with listeners,has now turned his attention to straight-forward farce. " Straight -forward " is notperhaps the word to use, as " CrackedIce," this clever young man's latest effort,which is to be broadcast on September 14th,is i wildly complicated affair, in which aretired Chicago racketeer and his sociallyambitious wife figure in a series of divertingsituations. It is only necessary to add that" cracked ice " is gangster slang for diamondsto enable listeners to have a very fair idea ofthe, plot. The producer will be Max Kester,and details of the cast will be announced later.

" The Squirrels' Cage"THIS radio play will be performed by

the Northampton Repertory Companyand produced by Owen Reed on August 23rd.The author, Tyrone Guthrie, was formerly aB.B.C. producer, and then returned to thetheatre; he is to produce at the Old Vicnext season. His other radio play, " TheFlowers are not for you to pick," hasalrea,dy had a Midland production. TheNorthampton Repertory has been runningfor ten years ; its producer, Bladon Peake,went there from the Abbey Theatre, Dublin,and was formerly at the Crescent, Birming-ham. The Company's last studio play was" Ceesar's Friend."

B.B.C. Scottish Orchestra

ON August 27th, the B.B.C. ScottishOrchestra, led by J. Mouland Begbie,

and conducted by Ian Whyte, will broadcastthe Suite for Orchestra, " Straloch," by Erik Chisholm, the Tone Poem, " Villon,"by William Wallace, and the Overture" In Autumn," Op. 11, by Grieg ; whileGeorge Fleming (bass baritone) will singwith Orchestra "Si tra i ceppi" (Berenice),by Handel, " When the King went forth

to War," by Koene-man, and, withoutorchestra, " The Balladof Sommerwater," byArmstrong Gibbs,

When Lights gorolling round the

Sky," by John Ireland, Invictus," byHahn, and " Old Clothes and fine Clothes,"by Martin Shaw.

"Morlais Castle Day-dreaT"

"MORLAIS CASTLE DAY -DREAM,"

a dramatic feature by Jack Jones,author of " The Rhondda Round -about"and " Black Parade," will be broadcast onAugust 26th. Morlais Castle, a crumblingruin, overlooks the stricken borough ofMerthyr, a borough which to -day hasfourteen thousand unemployed. MorlaisCastle stands a reminder to the sufferingpopulation of the borough of the days whentheir forefathers suffered under Normanmisrule. Reminiscent of even earlier timesare the Roman roads and remains, andthe parish church of Merthyr, standing onthe spot where the martyr Tydfil suffereddeath it the hands of the pagans, takes usback many hundreds of years. The twochief characters in Jack Jones's dramaticfeature are Dai and lanto, two unemployedmen, into whose dreams come severalvisions of the town's past. This pro-gramme will be produced by T. RowlandHughes.

August 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS

Firstlyeveryone taking an intelligentinterest in radio will find muchof interest in the Westinghouseproducts shown on Stand 36,Radiolympia. The exhibit includesWestinghouse Metal Rectifiers forboth H.T. and L.T. Supplies,Rectifiers for High Voltages suchas are used for Television, andWestectors f o r DistortionlessDetection and A.V.C.-each repre-senting the most economical,efficientunit for its particular purpose.

andSecondly

every keen student of radio shouldmake a point of getting a copy of" The All Metal Way, 1937." Itis recognised as the standard hand-book on metal rectification as appliedto radio. Contents include chapterson A.C. Mains and Universal Radio,Trickle Charging, EnergisingMoving Coil Loudspeakers fromA.C. Mains, the use of Westectorsfor Distortionless Detection, A.V.C.,and Battery Economy circuits, etc.,etc. If you cannot visit Radiolympiasend direct to Dept. PRA for yourcopy, enclosing 3d. in stamps.

CIW E STINGHOUSE es)WESTINGHOUSE BRAKE & SIGNAL CO., LTD.,

82, YORK ROAD, KING'S CROSS, LONDON, N.1.

RADIOLYMPIA

STAND 36

579

Be your ownService

The D.C. AvoMinor

CURRENTo-6 milliamps0-30 ,,0-120 ,,

VOLTAGEo-6 volts0-120-120 ,,0-240 It0-300 0-600RESISTANCE0-10,000 ohmso -6o,0000-1,200,000 0-3 megohms

The UNIVERSALA \e'OMINOR

D.C. VOLTS A.C. VOLTSo- 75 millivolts o- 5 volts0- 5 volts o- 25 0- 25 0-100 0-100 0-250 0-250 0-5000-500 RESISTANCE

MILLIAMPS o- 20,00o ohm,0- 2.51111111aMpS 0-100,000o- 5 0-500,0000- 25 o- 2 megohms0-100 0- 50-500 0-10

BRIT} S H MADE

The

Radiolympia

Stand 3 IYou MUST be able to testyour set accurately if recep-tion is to be kept at itsbest. With an AvoMinoryou can quickly trace faults.As efficiently as a serviceman you can go straightto the causes of crackles,fading or breakdown. Yourset can be tested fromA to Z-valves, circuits,components, batteries andpower units.

There are two modelsof the AvoMinor-D.C.and Universal. Each pro-vides you with a combina-tion meter of high accuracy,covering a wide field ofmeasurement.

See the AvoMinors atRadiolympia-or write fordescriptive literature.

EVERY TEST -with ACCURACYThe AUTOMATIC COIL WINDER& ELECTRICAL EQUIPMENT Co., Ltd.

Winder House, Douglas St.; London, S.W.1. Tele.: VICtoria 3404-7.


Developingthe Detector11111111111111111111111111111 stageThis Article Gives Details of the Variouswith Their Advantages and Disadvantages

DISTORTION in a receiver is commonlyassociated with the output valve, butthe fact should not be overlooked that

distortion can also occur in one of the earlierstages-especially in the detector stage.It is now recognised that detector distortionis governed to a great extent by the per-centage modulation of the transmitter, andtherefore a brief explanation of this little -understood term will be given.

Types of Rectifier

By IDRIS EVANS

August 22nd, 1936

ff,./c C,41,04 -E -

000/

Fig. 2.-Showing a battery -type

stage, and consequently a good deal ofexperimental work has been done in eon-nectioniwith various types of detector duringthe last two or three years, with the resultthat the best of the present-day detectorscan be relied upon to give practically dis-tortionless rectification.

Triode DetectorsDetectors can be separated into three

0/McoTo Z Foe0Z/77,0z/7'

68 -

ft 7: -

triode used as a diode.

damping effect on the preceding tunedcircuit.

The leaky -grid detector, on the otherhand, is used extensively in battery -operated sets, and also in many mains sets.When correctly adjusted this type ofrectifier can give practically distortionlessrectification. In a battery set slight dis-tortion is to be expected, as sufficientvoltage cannot be applied to the valve

7:7 C29Oz/r.our.

oi

1/4,q/41.2

(pnov-1h--cAtg-A-

/11. coo/4460

Fig. 1.-An H.F. pentode used as a detector. Fig. 3.-The circui arrangement of a mains double -diode valve.

Percentage ModulationMost readers are aware that telephony

transmitters use a carrier wave of highfrequency for carrying the electrical equiva-lent of the sound waves set up by thespeaker's voice or musical instrument in thestudio. The sound waves are superimposedon the carrier wave so that the currentamplitude of the latter rises and falls inaccordance with the pressure changes of thesound wave. In order to avoid transmitterdistortion the increase in the carrier currentdue to the superimposing of the sound wavemust be less than the normal amplitude ofthe carrier current, and the ratio of thecurrent increase to the normal current isreferred to as the percentage modulation ;with 100 per cent. modulation the increase isequal to the normal current amplitude.When the transmitter employs a modula-tion of 100 per cent. the input to thereceiver detector must vary between twicethe normal carrier amplitude and zero.Up to the present, however, no detectorhas been. found which has a straight curvefrom zero to maximum, and thereforedistortion must occur when 100 per cent.modulation is used. A few years ago itwas customary to use a modulation depthof 50 per cent., and therefore detector dis-tortion was not so prevalent as it is to -day,when the depth of modulation is generallyabout 80 per cent. This increase in themodulation percentage has necessitatedgreater care in the design of the detector

main types, namely, triodes, diodes, andthe metal type. The triode type can againbe divided into two classes-anode bend,and leaky grid. The anode -bend detector,commonly used in the old days, is seldomemployed nowadays owing to the fact thatit has been found to distort more than theother types. It has the advantage over theother types, however-it does not materiallyaffect selectivity as it imposes a very low

Fig. 4.-The circuit arrangement of a mains double -diode -triode.

anode in most cases, but when a mainssupply is available and a mains triode is used,the leaky grid rectifier will give a verysatisfactory performance-sufficiently goodfor use even in a " quality " receiver.

The circuit arrangement of the griddetector is very simple, and is well knownto most readers, but the required componentvalues are not so well known. In order toobtain good results the anode resistance

must be over four timesthat of the valve. This, ofcourse, necessitates the useof a high H.T. voltage,and accounts for the diffi-culty in obtaining reallygood results from a battery -operated valve. It is alsonecessary to keep the inputwithin certain limits, andtherefore a pm -detectorvolume control is essential.Distortion can occur due

o/ /WAD to the use of too low aninput, as well as to anexcessive input, and it isadvisable to connect amilliampeter in the anodelead of the valve in orderthat the correct input canbe checked. A valve shouldbe chosen which has ananode current consumptionof approximately 6' mA,



n Liourkivelen thSome Amusing ExtractsI WAS somewhat amused as well

as surprised to read in one of thedailies which boasts of a " technical "radio feature an article dealing withsome of the new wireless receivers.I learn that one of these new receivershas " a super -inductance circuitwhich empowers the receiver for useon A.C. or D.C. mains." I read ona little further and then discoveredthat another remarkable feature ofthis new set is that it has " iron -covered coils," which are " moreselective than air -covered coils." Thechoice bit was, however, to come." Sensitivity was of a very highdegree, a mere twist of the switchcutting one station out and bringingits neighbour in cleanly and easily."I do not know who was responsiblefor writing this tosh which unfor-tunately; or fortunately from thepoint of view of the printer, cannot beascribed to printer's errors. I do notknow what the manufacturers of theparticular receiver under reviewthought of it, but they must havehad their legs severely pulled as aresult, or else they have been pullingthe legs of some journalist whoobviously is not a technician. Eventhough they were printer's errors itwould be a case of careless proofreading, but even this must be ruledout.

By very kind permission-

I have often thought that our dailypapers do not take their radio,motoring, and cycling features suffi-ciently seriously. They do not seemto care what tosh goes in, nor dothey always select their contributorswith that care which the subjectdemands. I often try to imagine whatstyle of man it is who ,can get awaywith the sort of stuff I sometimes read,particularly when it is supposed tobe technical and authoritative. In

By thermion

the early days of wireless any sortof contributor could persuade somegullible editor that he was an expert,but nowadays there is no excuse forthat. I thought that all the unskilledwriters in radio journalism had beendiscovered and put " on the list " along time ago.

A Readers' LeagueMR. GERALD McCAFFIE thinks

that the recently mootedidea of a Readers' League wouldhe excellent if put into effect. Hethinks we ought to have a badgeso that readers can recognise oneanother, and form a link betweenhome constructors all over the BritishIsles. He thinks we ought to havethe Editor in it, too. I shall have tospeak to him about it. My corre-spondent invites me to live in Killarneyfor a hit so that I can learn somethingabout junk shops, or rather forgetabout junk shops, for he says thatthere are none in Killarney. For themost part, he tells me, you have tomake your own parts, or pay aridiculous price for them due to tax.He also invites me to spend myholidays in Killarney, an invitationI must accept next year, for I havenever been to Ireland. He says thatIreland is a backward country asfar as radio is concerned and theIrish would know very -little of radiobut for this journal, and Mr. Camm'sfine books, all of which he has securedby paying a tax of 5o per cent.Much obliged for your interestingletter, Mr. McCaffie.

Too Much Kind Permission

THIS film racket business isgetting worse than the croon-

ing affair. You will remember thatsome time ago I gave all readers andmankind generally my opinion of thefilm industry, in which the author ofthe film is mentioned last of all andthen merely by a flash of very smalltype. You will find that josh Leviskyproduced the film, that Ike Cohenvitchdirected it, that Ima Damfrost takesthe lead, that the film was photo-graphed by Abe Stinkski, that the

office boy was Tiny Timpski, and soon. Nowadays this system is percolat-ing through to the radio. I listened -into a musical comedy the other day,and was overawed by the fact thatMiss Dimplechin was appearing bykind permission of the Bunk FilmCorporation in conjunction with Mr.Pimp. Imagine my unboundedrapture when I was also informedthat another artist was going to useher larynx by kind permissian of theScream and Screech Films Inc., andMr. Pomp. These credit titles,although they are quite uninterestingto the public, are apparently insistedupon in order to give publicity tononentities. When I purchase ahouse I do not wish to know the nameof the bricklayer, but I do like toknow the name of the architect ; Ilike to know the author of a film,and not the name of the Director,who after all is only in the sameposition as the bricklayer. In radioI am interested in the singer or theartist ; I do not care two hoots whohas given her permission to appear ;I do not wish to know the name ofthe owner of a theatre ; I am onlyinterested in the people who appearon the stage. In the film and enter-taining industries you will find thehuman parasites and barnacles whobatten themselves upon the enter-tainers and wax exceeding fat. Each

Chaos reigns supreme

entertainer has to earn the living ofabout six other people, including theagent. When you hear of an artistearning £500 a week you mustremember that by the time all theseother parasites have had their pickinghe is lucky to have about kw clear.The most ignorant section of thepublic can be found in the productionside of the film industry. You haveall heard the story of the film magnatewho called together his staff to see


what ideas they had for the nextfilm. One of them suggested" Macbeth." " Who wrote it ? "asked the magnate. " WilliamShakespeare " was the reply. " Ihave never heard of him," said themagnate, " but send for him at once."That sums up the intelligence of theaverage person connected with filmproduction.

No advertising matter is allowedto be broadcast the B.B.C. ofcourse !

I shall be heavily disguised

The Eighth WonderEACH year I pop in to Olympia

on the night before the RadioShow opens, and each year I findthe stands in the same state of in-completeness, the same gang of work-men feverishly endeavouring tosqueeze two hours' work into one.Packing cases seem to be strewneverywhere, painters paint madly,char -ladies char frantically, barmenare busy barring, and even in therestaurants the waitresses are waiting.Chaos reigns supreme. Whilst I amsleeping, however, miracles seem tobe performed, for when I arrive in themorning every stand is spick-and-span.

No Bloodhounds, Please !

EACHRadiolympia time I realise

how many friends and enemiesI have made during the previousyear. Readers come along to thePRACTICAL AND AMATEUR WIRELESSstand and want to have a chat withThermion, please. I have stoodbeside them while they have madethe request, and although I have notactually seen the smoking bombsprotruding from their pockets, I haveoften caught a rather ominous glintin their eyes. Really, dear readers-my very gentle dear readers-yourUncle Thermion may have troddenon your very pet corn in print, butremember, my very charming readers,that kindness turneth away the wrath.Bunches of flowers for me may beleft on the stand, but all cases ofwhiskey, boxes of cigars and motor-cars should be wrapped up, sealedand marked " Confidential." I shallbe there again this year, quiteincognito, of course-and heavilydisguised !

Push-pull Transformer

MOST " quality " receivers andamplifiers are fitted with a

push-pull output stage, as it isgenerally recognised that this typeof circuit provides a practically dis-tor tionless output if the correct valvetypes and components are used. Asmost of the available push-pull trans-formers are somewhat expensive, andtwo valves are required in place ofone, the majority of constructorshave adhered to the single outputcircuit arrangement. With the reduc-tion in the price of valves it is probablethat the push-pull amplifier willbecome more popular, however. Theinitial outlay can be further reducedby using a straight transformer inplace of a push-pull type.

Reducing Cost

REASONABLYgood transformers

of the straight type are availablefor about los., and if a componenthaving a step-up ratio of about 4:Iis chosen this may be centre -tappedby means of resistances. Two resist-ances of reliable make having a valueof approximately 25o,000 ohmsshould be obtained. One of theseshould be connected to the G. ter-minal of the transformer and theother to the G.B. terminal, the freeends of the two resistances being thenjoined together and connected toG.B.- in the case of battery -operatedsets and to the H.T. - line in mainssets, with the G. and G.B. terminalsconnected to the valve grids. Thistype of circuit cannot be expected togive quite as good results as oneusing a well -designed expensive centre -tapped transformer, but the qualityis, nevertheless, exceptionally realistic.

Condenser Voltage Ratings.THE haphazard choice of con-

densers often gives constructorsa good deal of trouble. It is notsufficient to choose the correct cap-acity values-the condensers mustalso have the correct voltage rating.It is fairly easy to decide the requiredrating when designing a batteryoperated set, as the maximum voltagein the set is known to be 15o voltsor less. The condensers used should,therefore, have a working voltagerating of 15o volts or higher. In amains -operated receiver, however,a good deal of calculation is oftennecess

August 22nd, 1936

Taproom TopicsWAS touring round the other

day and dropped into acountry pub which I used to visitmany, many moons ago. In thosedays the favourite topic of conversa-tion was beer and turnips, and thesecond favourite topic was turnipsand beer. Imagine my surprisetherefore when a modern yokel,complete with old school kerchief;came in and asked for a Gin and It.Old Harry, who is now ninety-four,

With old school kerchief

dropped in, and although he stillstuck to beer his conversation be-trayed the influence of higher educa-tion. He was keenly interested in ourchances in the Olympic Games andgave me his private views on thepolitical situation in both the NearEast and the Far East. The wholevillage had been modernised by theB.B.C. and I imagine that all meetingsof the parish council are carriedthrough on the strictest Parliamentarylines.

Voltage SurgesIF a metal rectifier is used in con-

junction with indirectly -heatedvalves the smoothed voltage, duringthe time the valves are heating upis decidedly higher than normal ; forexample, with an H.T.8 rectifier theno-load output will be approximately45o, and therefore smoothing con-densers and anode by-pass condensershaving a working voltage rating ofover 450 must be used. High voltagesurges can also be experienced in areceiver having a high -resistancesmoothing choke or speaker fieldwinding in the common H.T. supplylead. During the time the indirectly -heated valves are heating up thecurrent passing through this highresistance will be very low, andtherefore the voltage drop at thispoint will also be low, and con-sequently the voltage applied to thevalve anodes will be high. In areceiver of this type the voltage ratingof the condensers must be higherthan the normal anode voltage. Thevoltage surge in this case could, ofcourse, be avoided by using oneof the indirectly -heated rectifyingvalves.

August 22nd, 1936 PRACTICAL AND AMATEUk WIRELESS 583

A FOUR -PURPOSE UNITA Simple -to -build Device Which May be Used as a Crystal Set, aWavetrap, a Wavemeter, or a Second -channel Whistle Eliminator

By W. J. DELANEYALTHOUGH designed primarily for

the beginner, the novel unit de-scribed in this article will be

found of great value by many listeners, asit may be put to so many differentuses. As explained above, it can be usedas a self-contained crystal set, or as awavemeter for the location of stations(or the identification of unknown stations)on any waveband, and also as a wavetrapfor the elimination of an unwanted stationwhich intrudes upon a wanted programme.For those listeners with a simple superhetreceiver in which trouble from second -channel interference is experienced thedevice may be equally as well employedas an eliminator of this trouble, and thechange from one piece of apparatus to theother may be carried out in a second ortwo.

Fig. 1.-General view of the four -purpose unitand the theoretical circuit which is employed.

In Fig. 1 the main essentials of the unitare shown in both a pictorial and a theo-retical form, and it will be seen that a tunedcircuit provided with a tapping pointforms the basis of the device, with twopairs of terminals arranged across thetapped portion of the circuit. The coilis home-made, and it is suggested that theconstructor makes a complete set of thesecoils to cover all wavebands in order thatthe device may have universal application.Across one pair of terminals (marked Bin Fig. 1) a small fixed condenser is con-nected, the value most suitable being.001 mfd., but any value near to this maybe used if the constructor has one handy.

The ConstructionAn important component is the tuning

condenser, and if the unit is to servemainly as a wavemeter the condenser

should be of the best make the constructorcan afford. Furthermore, a really goodslow-motion dial should be fitted, andshould be of the type which may be lockedfirmly in position so that no change incalibration can occur. The condenseris mounted on a small ebonite panelwhich should be of such a size that it willenable the terminals to be neatly spacedround it-in practice it will probably befound that a piece 6ins. square will proveadequate. A box should then be con-structed to contain the condenser, andagain a depth of six inches will enable theunit to take on a useful size, so as toaccommodate the largest of the tuningcoils. The wiring to the seven terminalsand the tuning condenser is shown inFig. 3, and the coils are made up as shownin Fig. 2.

Lengths of ordinary cabinet mouldingare used for the coil formers, and the generalshape of this moulding is shown in Fig. 2.The moulding is about Bins. in width,and the two end sections are raised above the'moulded portion. The wire is wound inthe latter, and when finished a length ofgummed brown -paper tape (such as isnow used for sealing parcels) is stuckacross the moulding to give a neat appear-ance and keep the wire from moving andupsetting any calibrations which aremade. The tape may be obtained for 3d.a box at the popular stores.

GUMMED PAPER STR/P1,

7\P1//RE TURNS

WOODMOULD/NG

Fig. 2.-Details of the coils used in the unit.

The CoilsFor the largest coil the former should

be made with sides to fit the sides of thebox, and if the above dimensions arefollowed, six inches will be sufficient. Thepieces of moulding are nailed together withbrass nails, and may be glued or seccotinedif desired. The three brass arms attachedon one side should be spaced to agree withthe three terminals shown on the left of

Fig. 3.-Wiring diagram showing the few simpleconnections.

the panel, and it will be noted that thetapping connector is placed to one sideso as to ensure that the coil is alwaysplaced in the correct relative position andcannot be reversed. For the medium -waveband 24 turns of 22 gauge D.C.C. wireshould be wound round with the tappingpoint 8 turns from one end. For longwaves, 120 turns of fine wire will haveto be put on, and if you have some wireby you which is of such a thickness thatit cannot be accommodated in a singlelayer the wire may be pile wound insections. For the shorter wavelengthsvarious coils may be made up, and as thenumber of turns will be so few the sizeof the former may be reduced, and thiswill, incidentally, enable the various coilformers to be nested one inside the otherfor storage purposes.

The Plug -on UnitsTo enable the unit to be used as a crystal

set or wavemeter, a crystal, a buzzer, anda battery are required, and these are allmounted on small panels of plywood towhich two brass arms, as in the case of thecoils, are fitted. These arms must, ofcourse, be spaced to correspond with thespacing of the terminals on the panel.To one panel the crystal detector is mountedand this may be of any type preferred bythe constructor. The permanent type isnaturally more reliable and is less trouble-some to adjust., The buzzer, to give bestresults, should be of the special high -notetype, provided with a shunt, and a suitablelow-priced unit may be obtained fromElectradix Radios for 6s. A disusedelectric -bell movement may be adapted,but is not so useful nor so neat. Thebattery may be a standard 4.5 volt flash -lamp battery, held to the appropriatepanel by means of a strip of thin brass,as shown in Fig. 4.

Using the UnitIn Fig. 5 the various connections for

using the unit are given. When it isrequired as a crystal set the aerial isattached to terminal No. 1, the crystalis plugged to the pair of terminals at theside, and the 'phones are connected acrossthe terminals opposite the coil. An earthlead should be attached to terminal No. 3.The crystal is adjusted for maximumsensitivity, and the tuning condenser isoperated in the usual way.



A FQUR-PURPOSE uNrr(Continued from previous page)

When used as a wavemeter, the buzzeris plugged in. place of the crystal, andthe battery in place of the 'phones. Theaerial and earth leads are not, of course,then required. The buzzer will com-

l."

Fig. 4. The threeessential add-on unitsare made up as shownhere. The Switch onthe battery panel maybe omitted if desired.

t

mence to work the moment the battery isconnected if there is no switch, but itmay be stopped by removing the batteryfrom the terminals, pr alternatively a smallswitch may be mounted on the battery

-

panel for the purpose.. The appropriatecoil is p/ugged in, and the wavemeter mustthen be calibrated. To do this a knownstation should be tuned in on your broad-cast receiver, and the wavemeter shouldthen be plaCed close to the aerial lead to thereceiver and the buzzer set into action.The dial on the wavemeter should thenbe turned until the noise from the buizeris heard in the loudspeaker. If a criticalsetting cannot be found the wavemetershould be moved farther away, until aposition is found where the buzz is tunedin and out in a fraction of a degree. Thispoint is then noted and the dial may bemarked or a graph may be drawn up onsquared graph paper. z -

A number of known stations are simi-larly tuned in and the resultant positionsmarked off on a chart so that the exactwavelength for each degree on the dial isshown. -

Then, if an unknown stationis located,the wavemeter is brought into 'operationand its exact wavelength may be ascer-tained. Alternatively, if a station is requiredand the wavelength is known, the wave -meter may be set into operation and tunedto that wavelength, after which the receivercontrols are operated until the buzz isheard. You will then know that the receiveris adjusted to the correct wavelength.

As a WavetrapTo use the device as a wavetrap there

are three separate alternative connections,each of which should be tried in turnto find the most suitable for your particularlocal conditions. The aerial may, forinstance, be attached to terminals Nos.1, 2 or 3, and terminals Nos. 3 or 2 maythen be attached to the broadcast receiver.Thus, all signals have to pass through the

unit before reaching the tuned circuitsof the receiver, and in the event of a stationcausing interference the wavetrap con-denser is simply adjusted until the, inter-ference is removed. The .receiver may thenneed slight re -tuning to obtain maximumvolume. e-,:=-4!.

To eliminate second -channel whistlesthe same procedure as mentioned aboveis adopted, and the wavetrap is adjusteduntil the station causing the whistle iseliminated. This will generally be the power-ful local, although when there are twopowerful local stations such as are found inmost parts of the country, it is possible thatwhistles may be set up by both, andtherefore, for the complete elimination ofthe whistles, two such traps will have tobe arranged in series in the aerial circuit.

TOSET

TOSET TO

SET

Fig. 5.-The. varicus uses to which' the unit rm.!)be put are illustrated above.

5 -METRE TESTS ON SNOWDON

ANUMBER of North Wales amateurtransmitters, Messrs. G. A. Massey(G6YQ), F. J. E. Starkey (G6KY),

J. H. Wood (G5YP), and A. K. Cardwell(2AKD), are climbing to the summit ofSnowdon on Sunday, August 23rd, to con-duct a series of 56 Mc. test transmissions.Two transmitters with inputs up to 10 watts,equipped for 'phone and modulated C.W.,will be used, operating under the call -sign G6YQP, between the hours of9 a.m. (09.00 B.S.T.) and 6 p.m. (18.00B.S.T.).

Schedules have been arranged with dis-tant transmitters with a view to increasing,if possible, the present record for two-waycommunication on :the 56 Mc. band.Numerous tests with different radiatingsystems will be made, and to each test willbe assigned a check number. All stationsreporting reception are particularly re-quested to include the reference numberand time in their reports.

Messrs. Stratton and Co., of Birmingham,through their station G6SL, and Mr. E.,Menzies (G5MQ), of, Liverpool, have signi-fied their willingness to co-operate withG6YQP. Mr. W. Jones (060K) will alsobe operating a transmitter from the top ofThe Great Orme, at Llandudno.

It is hoped to have transmitters also inoperation on the " Cat and Fiddle," nearBuxton, " Ashurst Beacon," near Ormskirk,Lanes, and in the Isle of Man. It is alsounderstood that two Irish transmitters,EI6F and EI8G, will be operating portable56 Mc. transmitters near Dublin, on

August 23rd, and Mr. D. S. Mitchell(G6AA) is attempting to achieve two-way communication with these 'stationsfrom the top of Holyhead Mountain,in Anglesey.

All reports of reception of G6YQPshould be forwarded as early as possible toMr. J. H. Wood, " Deepdale," MarineRoad, Prestatyn, Nth. Wales. The or-ganisers of these tests hope that interestedlisteners and amateur transmitters through-out the country will assist by reporting all5S Mc. signals, either from G6YQP, orany station heard calling him on thatday.

Short-wave amateur transmitters carrying their apparatus to the summit of M2unt Snowdoncarried out recentiu.

or test:,

0.

tin



A Dial Improvement

MYS.W. set was fitted with a good

reduction drive on the tuning con-denser, but no provision was made forwriting on station names. I therefore madethe following alteration to enable these tobe inserted. The dial was raised from thepanel by a }in.' washer, and a pointer wasfixed to the central spindle, as indicated inthe sketch. Behind this a scale, cut froma piece of white celluloid, was attached bymeans of round -headed screws, after anopening had been cut in the panel to enablethe scale to be illuminated by two green4.5v. bulbs, which are fed from the L.T.supply.

The set was calibrated, and the nameswere then marked in blue ink.

This device, which is very easily made,has proved very useful on my S.W. set.-J. P. BRITTAIN (Sunbury -on -Thames).

CELLULOID SCALEFOR STATION NAMES

TWO BULBS WIRED ":2'.IN PARALLEL(GREEN)

11111'1111iiila1010u1111111111111

111111111111111114

0.`

FIXING SCREW WITH/8" WASHER .

A method of improving a dial by the additionof an illuminated station indicator.

Remote Control RelayFOR some time being inconvenienced

when using a speaker in another roomby walking to and from set to switch it off,I made the following control.

Obtain one old bell movement, lesscontact -breaker, and one " mechanicalreplacement indicator movement." Filean elongated hole in end of arm of indicatormovement and bend striking arm of bellmovement to engage with this, first, of3otrrse, removingball on end : also soldershort piece of brass on end of arm ifnecessary to close contacts.

Three separate wires or three -wire cable isrun from control board to remote position,where two miniature bell pushes are fixed.

One push energises this indicator move-ment, causing " trip " to fall and switchon set. The other push energises bellmovement, which switches off set. Thediagram, I hope, will explain itself. Oneflash -lamp battery lasts about eighteenmonths. Don't forget to leave switch ofset on.-G. FAULKNER (Cobham).

! THAT DODGE OF YOURS ! iEvery Reader of " PRACTICAL AND i

AMATEUR WIRELESS" must have !originated some little dodge which wouldinterest other readers. Why not pass it onto us? We pay 41.10-0 for the best wrinkle i

Isubmitted, and for every other item published !

Ion this page we will pay half -a -guinea. Turn ithat idea of yours to account by sending it

Iin to us addressed to the Editor, " PRAC- i

/TICAL AND AMATEUR WIRELESS,"George Newnes, Ltd., 8-11, Southampton

/iStreet, Strand, W.C.2. Put your name andaddress on every item. Please note that every

inotion sent in must be original. Markenvelopes " Radio Wrinkles." Do NOT

i enclose Queries with your Wrinkle.6.1141=4.10114011.11111...NNIMMIENNEED1 YINE.M.04115,041

Handy Fitments foi the Test BenchI HAVE found these assemblies very useful

in making different tests.The construction is clearly illustrated in

each case by Figs. 1 and 2, and the sim-

SPADE TERMINALEND.

SOLDERED.

CROCODILECLIP.

SOCKET.

HG I.

SOLDERED.

FIG 2.

Interchangeable spade and crocodile ends.

plicity of assembly is evident, the onlynecessities being soldering utensils, and apair of pliers. When soldering, hold theiron touching the underneath of the joint to

BANPLUGANA.

SOCKET.

TO BATTERY.

585

remove excess solder, and leave a " finished"appearance. It will be seen that the spadeand crocodile ends are quickly interchange-able.-T. COPPS (Ilford, Essex).

A Small Engraving MachineTHE accompanying diagram, which is

self-explanatory, shows a smallengraving machine made with an electrn-

BELL MOVEMENT.

TOBATTERY.

VIBRATING ROD,

HANDLE.

TUBE

A simple CHUCK.`engravingmachine.

NEEDLE,

magnet and armature taken from an oldelectric bell. A wooden handle, drilled totake the armature rod, is fixed to a bracket,as shown. By using gramophone needlesthe engraving point can easily be changed,when required. If used with a bell trans-former, a, 2-mfd. condenser should be con-nected across the " make and break" ofthe armature to reduce sparking at thecontacts.-S. Rum:Pug (Doncaster).

BELL BOBBINS,

CONTACTSFROM OLDJACK.

An easily -made remote control relay for use with an extension speaker.

INDICATORMOVEMENT.

SHORT PIECEOF BRASSSOLDEREDTO ARM,

ACROSSLOCAL SWITCCONTACTS.

SMALLPUSH BUTTONS,

a


\\\\\\\ \\ 411\ 11111111111114

0

AS distinct from an adaptor, a convertercomprises a frequency -changer andsometimes a radio -frequency ampli-

fier in front of it, operating on the ultra -short waves, which is intended to be con-nected to the aerial and earth terminals ofthe domestic set, so that it then acts as theintermediate -frequency amplifier plus de-tector and L.F. sections of an ultra -short-wave set. The problems of adjusting the -home set for high qualityreproduction in such cir-cumstances are greater innumber and complexitythan those associated withthe use of a simple adaptor.Obviously, it is importantthat the low -frequency sideshall be above suspicion,and all the points noted in the firstarticle on this subject apply equallyto the operation of a converter.But, in addition, a great deal can bedone to the earlier stages of the set.

ConversionA receiver to be used in conjunc-

tion with a converter must haveat least one valve prior to thedetector-that is to say it musteither have one or more radio -frequency stages or it must be asuperhet. In the case of thestraight set with one or two radio -frequency stages, these- stages actas the intermediate amplifiers of the ultra -short -wave combination, and the home setmust be tuned to an appropriate frequencyfor this purpose. If, however, the home setis already a superhet, there will be adouble frequency change, one from theultra -high frequency to the intermediatefrequency of the converter, and anotherfrom this value to the intermediate fre-quency of the home set. In both cases thecombination will have an intrinsic degreeof selectivity equal to or even considerablygreater than that of the home set and this,as has already been pointed out, is alreadytoo great for really good quality. Theproblem confronting the listener, then, is tocounteract the poor quality engendered bysuper selectivity, and this may be doneaccording to two plans. The .first is tomanufacture a spurious quality by anadjustment of the values of circuit com-ponents, boosting the treble where possible,and partially suppressing the bass. Thesecond is to reduce the overall selectivity ofthe combination.

Relative MeritsNow with regard to the relative merits

of the two systems. Synthetic quality isreally not the most satisfactory for three

August 22nd, 1936

H 0 IRT WAVESECTION '

Artificial Aids to Quality on the U.S. Waves-Part 2Points to be Considered when Using a Converter, and Hints on ToneCorrectors -are Given in This Article. By H. J. BARTON CHAPPLE, B.Sc.

reasons. In the first place, boosted topdepends upon producing resonant circuitstuned to the higher audio -frequencies, andthese are naturally more effective at certainfrequencies than at others. The top boost,therefore, is not an overall boost, but apeaking at certain frequencies, and canalways be recognised as such by the music -lover. Second, suppression of the bass tolevel up the audio -frequency response curve

A useful commercial converter-the Vidor Batterycovering the Band from 13 to 50 metres.

means an overall reduction of output, whichis not only wasteful but prevents thespeaker from giving of its best. It intro-duces losses in all parts of the low -frequencyrange, although the losses are greatest atthe bass end, but the whole thing tends tosound artificial and unsatisfactory. Third,the fitting of the .necessary correctors andfilters means alterations to the circuit-allof which must be withdrawn in order toreinstate the receiver for normal wavereception. Now since the use of the con-verter may represent quite a small portionof the time during which the set is in service,it does not seem worth while to fit thesedevices, and to remove them every time itis desired to revert to the medium or longwaves, as otherwise whatever residual side -band splash gets through the early stagesof the set will be unduly amplified in theL.F. stages. However, as some readers maywish to experiment on these lines, a fewgeneral hints for doing so will be given later.

The idea of reducing the overall selec-tivity for ultra -short-wave reception is muchsounder from a radio engineering point ofview, gives infinitely better quality in thelong run, and the set can be reinstated forselective reception of the standard waveswithout much trouble.

AdjustmentsIf the domestic set which is being used in

conjunction with a converter is a straightthree, having only one radio -frequencystage, the initial selectivity may not be toogreat for quality reception if it is of thetwo -tuned circuit type. Naturally thereaction control, if any, must be turned toa minimum, and, if desired, a slightly widerintermediate -frequency waveband can be

obtained, by a slight variation ofone of the trimmers-not sufficient-ly to produce a very pronounceddouble hump. Some three -valvesets of this type have one band-pass circuit, which is usuallyadjusted to pass only 41- kilocycleson either side of the tuning fre-quency. It is sometimes possibleto readjust such filters to pass awider band by altering the valuesof the coupling components.

Another point worth investigatingis the normal selectivity of thedomestic receiver at various pointson its tuning range. Many sets in-corporate ingenious circuit arrange-ments designed to render. theselectivity uniform throughout thetuning range, but in some instancestuning is flatter in some parts thanat others. If, as often happens, thedesign of the converter is such thatthe intermediate frequency gener-ated can be adjusted to almost any

reasonable value, it may then be worthwhile to tune the domestic set to a pointcorresponding to the last selective part ofits range, and to adjust the intermediatefrequency of the converter to suit.

With a SuperhetIf the home set is a superhet, all the

points already enumerated may also receiveattention But when the best has been donein this connection, the ultimate selectivitymay be governed by the selectivity of theintermediate -frequency transformers. Nowit is possible to broaden the band width hereby altering the trimming of the I.F. trans-formers, but in view of the tricky natureof the job of re -trimming afterwards whenit is required to revert to normal listening,this practice is not recommended, at anyrate, in the case of a commercial set withsealed trimmers. With a home -constructedset, and particularly one having easilyaccessible trimmers, the experiment mightbe made by turning one trimmer througha definite amount, remembering just howmuch this amount is so that the set can beretrimmed without difficulty, or by re-placing the existing I.F. transformer in onestage by one embodying variable band -widthadjustment.

August 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS 5874111111.411041011,0041M.1014.111.0.0.1.01.0WINMIOME.0411k NIMEr011.=11141M{14Mil.=1.0.11=1.0.111{11).=...MPOINMPO.100.013.111.1.maiNno.0,

IMPROVING THE DET.-L.F. RECEIVERSeveral Suggestions for Modernising an

that can Easily

IN spite of the growing popularity ofsuperhets and similar advanced cir-cuits there are thousands of con-

structors who still prefer the populardetector-L.F. arrangement of valves. Aset using this circuit is of the simplestpossible kind, is easy to tune and does notcall for any special skill in connection withpreliminary adjustment. Additionally,of course, it is inexpensive and was oncethe most popular of all, Many readers

0002 11FD.

G .0005

?.0003Alfa

2/112

Old Set, and for Interesting Experimentsbe Carried Out.

fair selectivity on the medium -wave band,but it is not good enough on long waveswhen it is wanted to separate, say, Luxem-bourg, Droitwich, Radio -Paris and Hilver-sum. Much better results can be obtainedby using a coil with separate aerial andtuning windings, such as that shown inFig. 2. The coil actually shown is theWearite " Uni-Gen," but there are similartypes in other makes which will provesimilarly satisfactory.

H. r#) 60-80e

25-M0004

-0/PIRO.

G.

C>L. S.

HTt

HI-

k L.T. -

Fig. 1.-A typical del.-L.F. circuit, of the type which was popular a fewyears ago, and which is taken as an example when dealing with refinements.

who built an instrument of this type a fewyears ago have found it so satisfactorythat they are loath to scrap it, even whenit is decided to build another and moremodern receiver. Because of this, it mightbe considered worth while to spend a fewshillings in order to improve the set byadding a few modern refinements; thesewill certainly make the set more sensitiveand give it a degree of selectivity more inkeeping with present-day requirements.

The Tuning CircuitLet us, therefore, consider the improve-

ments which can be made without alteringthe main characteristics of the " oldfriend." We must deal with the questionin fairly general terms, because smallvariations must occur even in sets of thesame type. As an example, however, thecircuit given in Fig. 1 can be taken asrepresentative of the popular three -valve,non-H.F. receiver. Resistance -capacitycoupling is used between the detector andfirst L.F. valves, whilst a transformercouples together the two low -frequencystages.

The first and most important alterationshould be in the tuning circuit, since thecoils made to -day provide far betterselectivity than did their counterparts of

I a year or two ago. In the circuit shown,I the aerial is joined to a tapping on the

medium -wave winding, and this does give

Better ReactionIn order to use the new coil (if it is not

fitted with built-in wave -change switch)it is necessary to replace the existing two -point switch by one having three contacts ;this serves to short-circuit long -wave

0903 rif,o.

0005 MAO 4 RFC.PRE-SET

(OPTIONAL)

POINT pv/c SWITCH

2M/2

h. 0-10-4.7.--/-

.

Fig. 3.-A further development of the circuit!shown in Fig. 2, where an H.F. pentode (e.g. iCossor 210 S.P.T.) is used for detection. Notice!the use of a 3 -point on -off switch to disconnect the!

potentiometer when the set is out of use.

windings on both aerial and tuned -gridcoils. Another point to notice is thatthere is a tapping on the grid winding towhich the grid condenser can be connectedwhen maximum selectivity is required. iiThe reaction circuit shown in Fig. 2 is also !

.75-613000-0-N Ri 022 modified from that IHT+ in Fig. 1, due to one/20 g end of the reaction

winding being per-manently con-nected to the lower -end of the gridwinding. A 250 -ohmfixed resistance isalso shown in serieswith the reaction

and al- -though this is notessential it is gen-erally valuable insmoothing reactioncontrol.

The next altera-

L.F

HT -

I

Fig.2-Showing the use of a more selective tuning tion concerns the Icoil, an improved reaction circuit and decoupling. detector - anode I

circuit, for instead Iof using a separate H.T. tapping, as in Fig.1, a decouplingresistance and condenser are "added so that the detector valve may takeits H.T. supply from the same wander plugas that used for the other two valves. I


20-/00,00032 /0,00062. /2-361!)10-1,(T-

/20 K> H.r-

B/PS RES.

.25I /IF°

J

re:4. L .774-

)x L.77-

Ii

Fig. 4.-A very modern two -pentode circuit evolved from the original three -valve arrangement shownin Fig. 1. Connections for automatic G.B. are shown in broken lines.

14M.01111.M/111/110111/11,1141MINIM. afllaelee


BEGINNERS' SUPPLEMENT(Continued from previous page)

Additionally, of course, this decouplingcircuit prevents instability when the H.T.battery is running down, and permits thedetector to operate more efficiently. Thevalues of condenser and resistance shownare not critical, but are average oneswhich suit most receivers.

H.F.-pentode DetectorIn the majority of cases it will not be

a necessary to alter the low -frequency partof the set, but one or two refinements inthis direction will be mentioned later. Animprovement which is definitely worthwhile is the replacement of the triode-

I detector valve by one of the H.F.-pentOdetype, as shown in Fig. 3. In this circuit

i the screening -grid is shown as being fedfrom a 100,000 -ohm potentiometer, but

a expense could be saved by taking the leadfrom the S.G. terminal of the valve-

! holder directly to a low -voltage tappinga on the H.T. battery. But the potentio-

meter is very useful, because it can beused as a subsidiary reaction control. The

a alteration in valveholder connections whenchanging to the H.F.-pentode valve aresimple enough, and consist only of takingthose leads which previously went to theanode terminal of the valveholder to a

I flexible lead which can be attached to thea anode terminal on top of the new valve,I and making the screening -grid connection! to what was previously the anode terminal

of the valveholder.

The Anode ResistanceTheoretically, the anode coupling resist-

ance, marked RI in Fig. 2, should be of avery much higher value than before if it isto match the impedance of the new valve,but in practice it is often found thatthe same resistance can be used withoutthere being any serious loss in efficiency.Nevertheless, the constructor is advisedto try one or two alternative resistanceswith values up to 250,000 ohms. It mightbe found that reaction cannot be obtainedwhen the value is more than, say, 100,000ohms, in which case this value will haveto be used. In any case, it might benoticed that for best results the voltageapplied to the screening grid must bereduced to a voltage much lower than thatnormally recommended-say, 12 to 36volts. The reason is that the anodevoltage also is appreciably below themaximum for which the valve wasdesigned. For best results with thiscircuit a 120 -volt H.T. battery should beemployed, when a total resistance of250,000 .ohms for RI and R2 can nearlyalways be used without adversely affectingreaction.

Working on this assumption, it is a goodplan-either experimentally or perman-ently-to replace RI and R2 by a'250,000 -ohm potentiometer connected as shown inFig. 5. The potentiometer must be a goodone, capable of carrying up to 1 mA, andthe portion on the right of the slider isused for decoupling, whilst that on theleft is for coupling. A suitable " balance "can easily be found by trial, after whichfurther adjustment will be unnecessary.

I

I

I

I

I

I

I

I

I

I

Using a Separate ReactorThose who do not feel prepared to go

to the expense of a new H.F.-pentodea detector might be interested to try the

effect of using a separate reactor valve,as shown in Fig. 6, where the first L.F.

14MENFIM4 1.110.1

valveis used as detector, the normaldetector being used for providing reactiononly. The main alteration is that ofchanging the .01-mfd. grid condenser and.5-megohm grid -leak for values of .0002-mfd. and 2-megohms respectively, andincluding an H.F. choke in the anodecircuit of the second valve ; in addition,the grid condenser is joined to the tunedcoil instead of to the anode circuit of the

Fig. 5.-A potentiometer used in place ofresistances RI and R2 shown in Fig. 2.

first valve. When using this arrange.ment the volume will not generally be asgood as before, but it might be found thatthe range of reception is noticeably in-creased. The volume could be brought

Fig. 6.-This skele-ton circuit shcws how;.wo triodes can beused for detection and

reaction.

back to normal by using a pentode in placeof the triode -output -valve. This simplymeans that the existing four -pin valve -holder must be changed for a five -pincomponent, and that the centre terminalmust be joined to the main H.T. +lead.

A Two -pentode CircuitThere may be some readers who would

like to " go all modern " by using pentodes


ENCYCLOPEDIABy F. J. CAM M 4th 51.(Editor of " Practical Edition net.and Amateur Wireless")

Wireless Construction, Terms, andDefinitions explained and illustrated

in concise, clear language.

From all Booksellers, or by post 5/6 fromGeorge Newnes, Ltd., 8-11, Southampton

Street, Strand, London, IV .C.2.

for both detection and low -frequency aamplification. This can be done byeliminating the second valve and changingthe three-valver into a two -valuer, usingthe circuit shown in Fig. 4. All of theexisting components are used with theexception of the second valve and holder,and the L.F.-valve grid -leak. The trans-former connections are modified, so thatparallel -fed coupling is used between thevalves. Despite the loss of one valve, itwill be found that reception is improved,in addition to which current consumptionis less than before, especially if a high -efficiency pentode, such as a Cossor 220H.P.T. is used for L.F. Although bearinglittle resemblance to the circuit in Fig. 1,that in Fig. 4 is formed in simple stages,without any change of " key " com-ponents, and without altering the generalconstruction of the set. Thus, the samecabinet can be employed, and the methodof operation is almost the same as before.The change is truly representative of" new sets for old."

Automatic Grid BiasA still further improvement to this

two -valve arrangement might consist of !using automatic grid bias, by means ofwhich the correct bias is always obtainedregardless of the condition of the H.T.supply. All that is necessary is to include I

I

I

I

I

ier4-

G

a fixed resistance in series with the H.T. -lead (shunted by a 25-mfd. electrolytic acondenser), and to change the G.B. -connection from the L.F. transformer, asshown in broken lines in Fig. 4.

The value of the resistance must be

L.7

L.7:-

calculated, but the method is not difficult.The best method is to find the total H.T. _current required by the set, by insertinga milliammeter in the H.T. -lead, divide

!this into the G.B. voltage required (4.5with the valve mentioned above), and jmultiply the result by 1,000 in order toobtain the value in ohms. As an example,suppose that the valves together take8 mA, the resistance required is 4.5/8multiplied by 1,000, or nearly 600 ohms. -In this case, a 500 -ohm and a 100 -ohm'!resistance could be used in series. As thevalue is not very critical, it would actuallybe satisfactory to use the 500 -ohm resist-ance alone, although when this were done athe H.T.-current consumption would be 7.increased by about 1 mA. Anothermethod would be to use a 1,000 -ohm avariable resistance and to adjust this tothe highest value consistent with good fquality reproduction, remembering thatthe higher the resistance the lower thehigh-tension consumption.

1.1410.1111.041/0,....if 1.1101.04=1.1111041..11.11.1.1.101.1.11.1111.0411.0.142m.lcm, i..0.11.1.114/6.0.=0.041110.1

1


IMPRESSIONSON THE WAX

By 71Onearm

14 ....Two Newcomers

ANEWCOMER to the Columbia liststhis month is Paul Kaul, thedistinguished French violinist. He

has chosen for his record Beethoven's" Romance in F " which was originallycomposed for violin and orchestra. Thenumber of this fine recording is ColumbiaLX 514.

Another newcomer to the list is TinoRossi, a Corsican, who is extremely popularat the moment in France. His fame has nowspread to this country and Columbia, inresponse to many requests, issue his firstrecord this month. He sings " Reviens,Cherie" (" Come Back, Dearest ") and" Des Peines d'Amour " (" The Pangsof Love ") both in French on ColumbiaDB 1649.

Sandler's " Carmen "THE Albert Sandler Trio, to be heard

on the is. 6d. Columbia series, areforging ahead with the lighter

classics.This month they play a finely arranged

fkntasy of airs from " Carmen " on ColumbiaRB 1430, and judging by the great interestin opera tb-day, this selection should finda ready appreciation.

Turner Layton's contributions for thismonth are " When Evening Comes" and" Lonely Street " on Columbia FB 1457, and"I'm a fool for loving you," coupled with" Au Revoir, but not Good-bye " onColumbia FB 1458.

King's Piano FavouritesTHE two Viennese pianists, Rawicz

and Landauer, who recently playedbefore the King, present two of their

own arrangements in the new Columbiaissue. They are " Schubert Time " and" Waltz Memories from Vienna" onColumbia FB 1431.

Selmar Meyrowitz, the French conductorwho was awarded " Hors Concours " forhis Liszt " Faust Symphony " recording inthe gramophone " Grand Prix," is aprominent figure in the Columbia list forthis month. He has chosen Wagner's" Siegfried Idyll " for his work. The musicis brief but fascinating, and is made up offour themes from the opera " Siegfried "and an extract from an old German cradlesong. The " Siegfried Idyll " is on twoColumbia 12 -inch records-DX 739-40,in the 4s. series.

" Electric " Guitar -Organ ToneTHE Spanish " electric " guitar record,

issued by Columbia a month or twoago, has proved a success as well

ads a novelty. It demonstrated, too, atriumph of British recording as over theAmerican, which failed in its attempt torecord this new instrument, and thereception accorded it has brought a sequelin the Hawaiian " electric " solos played byLen Fillis in this month's list. " SweetHonolulu " and " Lover, Come back tome " are the titles which appear onColumbia FB 1432.

Another " Spot of Bother "IN a variety broadcast last month Clapham

and Dwyer perpetrated a " spot ofbother " that had far-reaching results.

It was their " Surrealist " alphabet and itraised such laughter that they wereinundated with demands for records of it,so Columbia issue it this month, coupledwith " A spot of Fishing " on ColumbiaFB 1465. The " Surrealist" concoction,with its A for horses, B for Mutton, C forHighlanders, etc., is well worth hearing.

Novelties in VarietyHEADING the ls. 6d. variety records

in the latest supplement are theRocky Mountaineers, singing in

their breezy style, " It Ain't Nobody'sBiz'ness," " Oh Susannah," and " We'llRest at the End of the Trail," on ColumbiaFB 1433. They are accompanied by theBunk House Boys.

An all -marimba band is a rarity and thismonth appears Ring's Marimba Band in" Marimba Classico " and " Thanks for aBeautiful Day " on Columbia FB 1436.

On two pianos, Carroll Gibbons and JohnW. Green-staunch friends-play a cleverfantasy entitled " Two Friends inHarmony." Gibbons thinks he can do betterin Green's " Living in Dreams " than thecomposer himself. Green returns thecompliment with Gibbons' " On the Air"and both artists therefore play their ownversions with ingenious results. ColumbiaFB 1437.

Take Your PickWITH his Boy Friends, Carroll

Gibbons plays two tuneful hitsfrom the film musical " The

Great Ziegfeld." The titles are " You "and "You Never Looked so Beautiful" onColumbia FB 1459.

The organ finds a place in this list withSidney Torch on the London Regal Cinemaorgan playing " The Organ Grinder " and" The Cuckoo in the Nest " with brillianteffects-Columbia FB 1439.

Debroy Somers and his band essay acouple of well -liked marches in " Sons ofthe Brave " and " El Abanico " on ColumbiaFB 1440, while Les Allen and his CanadianBachelors sing " At the Close of a Long,Long Day " and " A melody from theSky " on Columbia FB 1456.

Regal-Zonophone ReleasesRACIE FIELDS, the ever popular

comedienne, records two very oldfavourites in her latest record.

The titles are " I'm a Dreamer (Aren'twe all)," and:' If I had a Talking Pictureof You "-Regal-Zonophone MR 2134.

George Formby contributes, in his usualstyle " The Pleasure Cruise " coupled with" Wash -house at the Back " on Regal-Zonophone MR 1952, whilst Leslie Saronysings two typical Sarony numbers in " Whenthe Territorials are on Parade " and" If Everyone did a Good Turn every Day "on Regal-Zonophone MR 2147.

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Address

B.B.C.Stands atRadiolympia

As inpast years, the

B.B.C. will havetwo stands in the MainHall during theNational Radio Ex-

hibition at Olympia, which opens next week.Apart from a comprehensive show of theCorporation's publications, there will be fourspecial feature exhibits which should prove ofinterest to all listeners. The first of thesewill consist of a series of six revolvingglobes showing by suitable colouring theareas served by the various Empire trans-missions. Another exhibit of unusualinterest to listeners of long standing willbe the original dramatic control panel thatwas in use at Savoy Hill for very earlydrama productions. The primitive appear -

August 22nd, 1936

By JACE

Leonard Henry, the Western Brothers,Nosmo King, and Les Allen and hisCanadian Bachelors. Broadcasts will beon August 27th, 31st, and September 5th.

There will be in addition two broadcastsduring the Children's Hour, on August 31stand September 1st. The well-known radio,personalities appearing on the former datewill be Commander Stephen King -Hall,David Seth -Smith (the Zoo Man), MabelConstanduros and John Rorke, RonaldGourley, and, of course, " Mac " (DerekMcCulloch). On September 1st the pro-gramme will consist of a " Toy Town "production, and music by the GershomParkington Quintet, in addition to DerekMcCulloch.

Music -HallERNEST LONGSTAFFE, ever on the

look -out for typical radio talent,presents a strong cast of music -hall artists

A NEW SOUND RECORDER.

The new Philips -Miller recording outfit, which has now been installed at the B.B.C. Maida Valestudios. This apparatus was described in our issue dated 8th August.

ante of this gallant relic will be enhanced163, its juxtaposition to a large photographand explanatory diagram of one of thelatest stream -lined dramatic control panelsat present in use at Broadcasting House.There will be a large chart showing theastonishing growth each year of the numberof licences issued from 1923 onwards. Andfinally visitors to the stands will see threelarge double -sided revolving discs ; oneach disc will be mounted photographs ofB.B.C. studios, masts and microphones ofvarious types, B.B.C. programme per-sonalities-the men behind the broadcasts-and famous radio stars.

RadiolympiaTT is announced that there will be several1. broadcasts from the Theatre at Olympiaduring this year's Exhibition, and amongthe artists whom listeners may hear areStainless Stephen, Navarre, Tollefsen,Clapham and Dwyer, the Carlyle Cousins,

for his programme on August 22nd. Twoacts make their first appearance before themicrophone on this occasion. The first isRay Meux, who is at once a comedian andsomething of a mystery. He has, underdifferent names, played leading roles inplays by Sheridan, Shakespeare, andMoli6re, as well as by contemporarydramatists, and has written, produced, andstarred in revue and cabaret. His realidentity is known only to Mr. Longstaffo,who has lately been engaged in giving himmuch the same process of secret groomingfor radio stardom as is undergone by new-comers of exceptional possibilities in Holly-wood. The second act consists of TomKatz and his Six Saxophonists. Wellknown on the music -hall stage in Londonand the Provinces, they present an attrac-tive combination of personal dexterity andclever arranging.

1st Big Show Number-Next Week


LETTERS FROM READERS- -

The Editor does notnecessarily agree withopinions expressed by his

correspondents.

Good Results with an H.F. UnitSIR, -A few weeks ago you published

details of an H.F. stage suitable foruse with an S.W. set.

Immediately on publication I made upthe unit, and used it in conjunction with a0 -v -Pen. S.W. battery set, with considerablyimproved results. You will recall the unithad two aerial connections, and after con-siderable experimenting I found I got thebest results by using both. No. 1 aerial is25ft. of 3/20 V.I.R. cable, 20ft. high at oneend and inclined at 45 degrees, withapproximately an east and west direction.No. 2 aerial is similar in size, but in a hori-zontal position approximately north andsouth. Both aerials lead into the set throughabout 8ft. of twisted flex. The results fromthis arrangement are really remarkable,especially as the aerials are screened by thehigh building, and the set is in the base-ment. -F. G. H. MACRAE (London, W.).

Proposed Amateur Sound RecordingSociety

SIR, -In discussing home recordingwith one or two fellow enthusiasts, it

was suggested that there must be manymore of us who would welcome the oppor-tunity of joining our discussions andexchanging ideas and experiences.

The outcome of this " gathering together"was a proposal to form the first AmateurSound Recording Society with the objectof arranging visits to places of interest ; ofhearing each other's results and generallyworking together to improve the standardof results obtained from this fascinatinghobby.

Interested readers are invited to write tome with a view to arranging a meeting tofurther the project. -Jas. P. BUTTERFIELD,

Manor Road, Beckenham, Kent.

Reports and PostageQ have just read in the Corre-

spondence section of your admirablepaper a letter from E. Barr (Andover), con-taining a request from W8ANO, with regardto SWL's sending return postage with their

-reports.Whilst on this subject, I have the converse

complaint to make. In March last I sentreports to SM5SI and SM1SX, both ofStockholm, and also to SU1CH of Cairo.Each report contained an InternationalReply Coupon, the one to Cairo being sentAir Mail to save time. Yet in each casemy time and trouble (and money) has beenwasted, since none of these gentlemen hasdeigned to reply.

It would seem that W8ANO has been therecipient of reports from SWL's who havealso had this same experience.--Gso.MILLER (West Ealing).

SIR, -It is time the question of QSLcards was taken up by amateurs and

explained to the general public.Firstly, the side of the transmitter must

be explained. Most of these amateurs areonly too pleased to receive reports on theirexperiments and contacts, and here a wordshould be said with reference to the cost,Say a station puts out a test call, it is


tion).

possible for over a hundred people in differ-ent parts of the country, or even the worldfor that matter, to hear the test, and perhaps75 per cent. of those who heard the testsend in their reports. Can you imaginewhat the cost will be to reply to all these ?

Most transmitters do their best to answeras many reports as they can, but there area lot of reports left unanswered, becauseof the great amount of work and theexpense it creates.

So much for the transmitter. Now comesthe worst part of the QSL business, theS.W.L. or BRS stations. There are a greatnumber of these who make it their hobbyto collect QSL cards, and in many caseswhen they require a return in exchangefor theirs they send stamped addressedenvelopes for same, but to date I havereceived no less than thirty-seven cardsfrom Australia and New Zealand, saying,here is my card, what about yours ? Thesethirty-seven cards have arrived within thelast four weeks, and at the rate they areincreasing it is going to be difficult to dealwith them in the future unless one employsa secretary to write out the replies. If theydo not get a card in return some of themmay take it the wrong way and think weamateurs are a stand-offish lot of fellows,

!but I think if this letter is published, andcomments pn the question asked for, itwould help very much in clearing up thematter, and save a lot of time and moneyon all sides. -W. T. COOPER (Waltham -stow).

Transmissions from W2XAD

SIR,-It may interest short-wave lis-

teners to know that W2XAD recentlyincreased its daily schedule of operationby one and three-quarter hours. Thisstation now operates daily, includingSundays, from 4 p.m. to 9.45 p.m. G.M.T.

When I received a letter from Schenec-tady a short while ago I was told thatW2XAD had a power of 18 kW, andW2XAF 27 kW. The maximum for whichthey are licensed is 25 kW for W2XAD and40 kW for W2XAF.-S. JANES (Croydon).

CUT THIS OUT EACH WEEK

THAT a number of cathode-ray tuningindicating devices will shortly be on the marketfor the use of the home -constructor.-THAT the high -note response of a loud-speaker may be improved by stiffening thecentre portion of the cone.-THAT the response curve of an L.F. trans-former may be modified or flattened by con-fleeting a resistance across the secondarywinding.-THAT soft copper wire for connecting pur-poses may be stiffened by stretching until it"gives." .i

-THAT even very thin wire will remainrigid over a considerable length when stretchedin the above manner.-THAT ordinary rock salt buried round theearth plate will improve its efficiency.-THAT all joints in the outdoor aerial systemshould be given a coat of paint or otherwiseprotected against corrosion.

A First AttemptSIR, -I like to thank you for the

book which I have received in con-nection with Problem No. 201, and at thesame time to convey my appreciation ofPRACTICAL AND AMATEUR WIRELESS, whichin its sphere is second to none.

However, I would like to see a largershort-wave section, and perhaps you couldfeature amateur DX in the " Leaves froma Short-wave Log " column. Throughyour short-wave section I became interestedin reception on the high frequencies, andlearnt enough to make a one -valver.Nothing very wonderful, I will admit,but I get fairly good results, consideringit is my first attempt.

I have recently logged a list of stationson 20 metres, as follows :-

W124, W1BDS, W1IF, WIZD,W1 EBO, W1AAK, W1IDB, W1DMB,W2BFB, W2CMT, W2HFI, W3IR,W3EKU, W3CZW, W3ABJ, W3NK,W3FIH, WSIKE, W8IRK, W9TB,W9BBU, W9JLR, CO7HF, HI7G, VE2EE,VE2BG, and VE3HC.-C. WRIGHT (Leeds).

A Suggestion for B.L.D.L.C.Members

SIR,-I have been thinking over a new

idea, and I wonder how many short-wave enthusiasts would care to help inthis new venture ? The suggestion is thata number of short-wave enthusiasts shouldsend their reports of a certain long-distancestation (over a certain period) to one short-wave amateur, who will sort out the datain the reports and forward the informationfrom them to the station in question(if possible, the data to be sent in theshape of a graph), a copy of the results tobe published in PRACTICAL AND AMATEURWIRELEss. The question is, who will dothis ? I will undertake the job of sortingand forwarding the data if interested readerswill kindly send me their reports. Here isthe first attempt :-

All short-wave reports of W8XK,19.72 m., 15,210 kc/s, for the month ofJuly, 1936, will be welcomed at the addressgiven below. Please give the followingparticulars : Type of Rx (receiver), antenna,signal strength in the R1-9 code, fading(QSB), interference (QRM), headphonesor loudspeaker. The time in B.S.T.( twenty-four hour system), and last, butnot least, the address (QRA). I hope thiswill prove successful, and, if so, we willcontinue with reports on other stations. -E. BARBS (4, King's Road, Enham, Andover,Hants.).

Reception of American Amateursrecently received the following

U.S.A. amateurs very clearly on theloud -speaker. W1CHG, CCZ, ESU, BTL ;W2BED, DH, CBT, ELO, MJ, BSD,ATV, CT ; W3BOP, SAY ; W4FM (Jack-sonville, Florida) ; W8BGF and W8ANO.

All stations were received between 23.00and 00.00 on 20 metres, using an 0-v-1transformer coupled to the pick-up terminalsof a commercial 5 -valve superhet. Thisarrangement provides plenty of volume,and is far more enjoyable than listening on'phoneii.

W2BSD, usually so strong, was surpassedby 2DH and 4FM, which came in R9 attimes ; in fact, I had to turn the volumecontrol on the mains set right down, toreceive it at comfortable volume. -A.NEEDHAM (Grantham).


COMPONENTS TESTED

New Midget Accumulators

IN OUR NEW LABORATORY

IN our issue dated August 1st last we gavefull details of the range of midget

accumulators manufactured by the A.E.F.Manufacturing Company. This range hasnow been extended by the addition of threenew types, known as CP5, WJ7, and BU7.The first is a 10AH type having a maximumdischarge rate of 1 amp., and the, price is 9s.The second is a 15AH type with a dis-charge rating of 1.5 amps. and costs 108. 6d.,whilst the third is of the 12AH type ratedfor a discharge of 1.25 amps. The priceof this model is also 10s. 6d. A completelist of all types and prices may be obtainedon application to the manufacturers at

1 7 , Queens -way, PondersEnd, Middle-sex.

New ClixFuse Plug

THE de-velopment

of connectingplugs alreadyfitted withfuses is wellexemplified inthe new Clixplug which isillustrated onthis page. Aswill be seen, in

This sectional drawing of the outward ap-new Clix plug shows the pearance this

method of construction. is very similarto the standard

5 -amp. type of pin -plug, but internallysmall clips connect the pin with the leading -in cable. Between these two points a fuseis inserted and -the fuses provided are of theclip -in type, fitting into the Clips insertedin the plug, and they thus form the linkbetween cable and connecting pin. 'Thelatter is of the well-known Clix non -collap-sible type and a firm and noise -proof contactis obtained in the standard 5 -amp. socket.The case of the plug is of brown mouldedhakelite, and the two halves are held to-gether ,by a single screw thus facilitatingquick repairs in the event of the fuse blow-ing. The price is Is. 8d., complete withtwo fuses.

Visual Tuning Indicator by MullardTHE Mullard Wireless Service Company,

Limited, will shortly be releasing anew visual tuning indicator which will heknown as the TV.4. It operates on theelectron beam principle and, possessing noappreciable inertia, its action is instanta-neous.

The TV.4 consists of a small triodedirectly coupled to a cathode-ray device.When no signal is being received theillumination of the screen is confined to agreen cross -shaped figure which spreadsover the surface of the screen as a stationis tuned in.

A compact size has been attained byfitting the tube with the Mullard side con-tact base. In this case the 8 -contact typeis used. The TV.4 is listed at 17s. 6d., but

the actual date of release has not yet beenannounced.

New AvometerANEW Avometer test instrument is

shortly to _ be pro uced by theAutomatic Coil 'Winder and ElectricalEquipment Company, Ltd. This is a forty-six range model,!embodying a protectivecut=out and temperature -compensatingdevice. The naostment is of the moving -coil type; but it is stated that it will notsupersede the thirty-six range UniversalAvometer which is already on the market.No prices or other details are yet released.

A new signal generator is also announcedand is of the continuous range type, "cover-ing from 3,000 to below 20 metres onfundamentals. It may be modulated, eitherinternally or externally, or may be adjustedto give a pure radio -frequency signal. Itis supplied complete with broadcast andshort-wave dummy aerials, valves, andbatteries, and the price is 15 guineas.

Aerialite BatteriesSOME new batteries are shortly to be

introduced by Aerialite, Ltd., and theprices of existing models are being reduced.The new prices are as follows : 120 volt,5s. 11d. ; 108 volt, 5s. Id. ; 60 volt, 3s.Previously the prices were 6s. 6d., 5s. 9d.,and 3s. 6d. respectively.

Percolite batteries are still on sale asbefore at 5s. 6d. for 120 volts and 2s. 10d.for 60 volts.

362 Valve Price Reductions

FIVEof the valves in the 362 mains

range are to be reduced in price,and these are the ACME4a, ACME4b,ACHE4, and ACSG4, the prices of whichare now 10s. 6d. The ACVP4 is reduced to12s. 6d. Full details of the 362 range ofbattery and mains valves may be obtainedon application to the company at StonehamRoad, Upper Clapton, E.S.

The new " Voluphone" produced by WharfedaleWireless Works.

August 22nd, 1936

Wharfedale LoudspeakersTHE -Wharfedale - Wireless Works are

pmducing some new models for theforthcomingexhibition, including a " Stan-dard " at 23s. 6d., a " Bronze " at 35s. anda " Golden " at 55s. The two former modelsare of the 8in. diaphragm type, and the" Golden " is a 10in. model. Six extensionspeakers are also announced at prices from30s. to £7. All these models, with theexception of the cheapest one, have a" Truqual " volume control fitted. Aninteresting unit is the " Voluphone." whichis a moving -coil unit for holding in thehand. It has been designed primarily forthose listeners who are hard of hearing, andis supplied in a blue rexine case lined withvelvet. The speech coil has a resistance of2 ohms and a transformer will be suppliedwhere desired at an additional cost of7s. 6d. A volume control is fitted. A uniton similar lines, but modified for use as amicrophone is also available at 25s.

REPLIES IN BRIEF 1

The following replies to queries are given inabbreviated form either because of non-compliancewith our rules, or because the point raised is not ofgeneral interest.

04=41.11.1 P.41.011110.11.11.1,=4 NMI 111110F. S. (Edmonton). There is, unfortunately, no blue-

print of a unit of the type you desire, and the onlyissue in which the construction of such a device wasdescribed is now out of print. We regret that we are,therefore, unable to be of assistance to you in thisparticular case.

R. S. (Patna). When you adjust the long -wavetuning you are only modifying the intermediate -frequency of your superhet combination and thisaccounts for the effect mentioned by you.

R. 0. S. (Tettenhall). We' have not described areceiver of the type mentioned, and do not think theordinary constructor would be prepared to go to theexpense of building such a set.

F. J. a. (Catterick Camp). A defective valve can giverise to the effect mentioned. The exact cause may beascertained by including a milliammeter in each anodecircuit in turn, when the fade out will be accompanied,no doubt, by a drop in anode current in the appropriatestage, and the exact cause may then easily be located.

J. MM. (Darlington) -Our is. Home Mechanic book,entitled " Accumulators -Charging, Maintenance, andCare," will, no doubt, prove of use to you. We do notknow of any book dealing with the other subjectmentioned.

E. G. W. (S.E.5). The Cossor 210 DET and220 H.P.T. would prove suitable.

H. S. (Halifax). You appear to have tried all thenormal tests and, therefore, the trouble may be outsidethe set, such as the microphonic response of someornament in the room, or a loose screw in a com-ponent, or vibration of a layer or portion of a layer ofwood in a plywood panel used in the cabinet.

J. N. (Doncaster). We have not reviewed the receiverin question, and can give you no details concerning it.

L. P. (W.6). We publish no handbooks on thesubjects mentioned, and do not know of any on theEnglish market.

F. 0. (Horsham). It is not possible to give you theinformation, as the capacity depends upon the areaof overlap and the spacing of the plates. Therefore,the size of the plates must be given and the spacebetween them before the capacity can be calculated.

D. M. (Bellgrore). We are sorry that we cannotidentify the transformer frbm the details given. Agood radio dealer should be able to trace out theconnections or test it, and give you the various voltagetappings.

M. C. (Birmingham). The Dutra 'Sheets may still beobtained, price 3s. 6d.

E. H. N. (Norwich). As the volume control affectsthe H.T. consumption, it will naturally have some effectupon the reaction control. But the details given byyou point rather to H.F. instability, due either tointeraction between the H.F. stage and the detectorstage, or between inter -stage wiring.

W. A. C. (Leis). The apparatus shown is an ordinaryS.W. adaptor, and therefore should have been used inplace of the detector stage in the £4 Superhet 4. Toconnect before the aerial you require a S.W. converter,and this will give much better results. The adaptorshown by you could be modified to act as a converter,but we cannot give full instructions for doing this in thissection of the paper.

W. T. q Homerton). We have no blue print of anamplifier of the type mentioned. Some A.C. amplifierswill be found at the end of our blueprint list.

E. P. A. (Sherborne). The frame aerial has theadvantage of being directional. That is to say, it willprove more selective than the indoor aerial arrangementmentioned by you. The addition of an H.F. stage willincrease the number of stations heard, but the additionof a further L.F. stage will give very little increase inthe number of stations, although the volume of existingstations will be greatly increased.

August 22nd, 1936 PRACTICAL -AND AMATEUR WIRELESS

RADIO CLUBSAND SOCIETIESClub Reports should not exceed 200 words in lengthand should be received Fi rst Post each Mondaymorning for publication in the following week's issue.

The West London Radio Society

THISSociety has now been in existence

for nearly a year, and the progressmade through the perseverance of itsmembers has been remarkable in such ashort space of time.

During the winter there were severallectures and demonstrations of sets given,but in the summer months, however, fieldand river days were found to be verypopular. Regular meetings for talks anddebates are held, and t committee meetingonce a week. Following the success of the5 -metre river day held on Sunday, June14th, the Society organised a similar outingon Sunday, July 19th. The success of thismeeting was even greater than that of theprevious one, the attendance being con-siderably increased. Interesting experi-ments were made throughout the day onthe 5 -metre band. Members of the Societywere asked to invite their friends, many ofwhom came and thoroughly enjoyed theirday on the river.

The Honorary Secretary would be verypleased to hear from anyone in the Westarea of London who is interested in any lineof radio.-H. A. Williamson, 22, CambourneAvenue, West Ealing, W.13.

DEVELOPING THE DETECTORSTAGE

(Continued from page 580)

when no signal is being received, withan anode resistance of about five timesthe value of the valve resistance ; mostmains triodes having a resistance ofabout 8,000 ohms are suitable. To obtaindistortionless rectification the inputmust then be regulated by means of theH.F. volume control so that the re-duction in the detector anode currentreading when a signal is being received isapproximately amp. When these operatingconditions prevail excellent reproductioncan be obtained. Fig. 1 shows an H.F.pentode used as a leaky grid detector..

The DiodeThe diode rectifier was superseded in the

early days by the triode owing to the higheramplification obtainable from the latter,but when the quality of transmitted pro-grammes improved and search was beingmade for a better form of rectification, itwas found that the diode possessed- advan-tages as compared with the triode. A diodewill produce -distortion when the input istoo low, but it is practically impossible tooverload it, and therefore it is very suitablefor use in multi -valve receivers. Fig. 2shows a triode used as a diode, and in Fig. 3is shown a special mains operated diode.It will be noted that the two circuit arrange-ments are very much alike, and examinationof Fig. 4 indicates the similarity betweenthe circuit arrangement of the double -diode -triode, and the diode used in con-junction with a separate triode L.F. valve.In valve booklets and receiver designs thedouble -diode -triode circuit arrangementlooks very complicated, and therefore thecomponents in Fig. 4 have been so arrangedto clarify what is actually a straight -forwardtwo -valve circuit.

593.

ONLY EXPERIENCE CAN BRING

DEPENDABILITY OF PRODUCT

THE TELEGRAPH CONDENSER COMPANY LIMITED.WALES P AR M ROAD N *ACTON LONDON W 3

0353



BLUEPRINT SERVICEPRACTICAL WIRELESS

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, Is. each.

Date of IS.S4IP. No. ofBlueprint

All -Wave Unipen (pentode) .. PW31A

Two -valve : Blueprints, Is. each -Four -range Super Mag Two (D,

Three -valve : Blueprints, Is. each.Selectone Battery Three (D, 2 LF

(trans.))Sixty -Shilling Three (D, 2 LF

(R.C. & trans.)) _ 2.12.33Leader Three (SG, I), Power) .. -Summit Three (HF Pen, I), Pen) 18.8.34All -Pentode Three (HF Pen, D

(pen.), Pen) . .. 22.9.34Hall -Mark Three (SG, D, *Pow.) ..Hall -Mark Cadet (D, LF Pen

(R.C.)) .. 16.3.35F. J. Camm's Silver Souvenir (HF

Pen, D {pen), Pen) (All -WaveThree) .. . .. 13.4.35

Genet Midget (I), 2*LF (trans.)).. June '35Cameo Midget Three (D, 2 LF

(trans.)) .. 8.6.351936 Sonotone Three -Four (HE'

Pen, HF Pen, Westector,Pen) .. . .. 17.8.35

Battery All -Wave Three (D, 2 IF(R.C.)) 31.8.35

The Monitor (HF Pen, D, Pen) .. 8.2.36The Tutor Three (HF Pen, D, Pen) 21.3.36The Centaur Three (SO, D, P) -Four -valve : Blueprints, Is. each.Fury Four (2 SG, D, Pen) ..Beta Universal Four (SG, D, LF,

1(ucleon Class 13 Four (SG,(SG), LF, Cl. B).. .. 6.1.34

Fury Four Super (SG, SG, D, Pen)Battery Hall -Mark 4 (HF Pen, D,

Push -Pull)

Mains Operated.Two -valve : Blueprints, 1s. each.A.C. Twin (13 (pen), Pen)..A.C.-D.C. Two (SG, Power) ..Selectone A.C. Radiogram Two

(D, Pow.)

Three -valve : Blueprints. Is. each.Double -Diode -Triode Three (LIF

Pen, D.D.T., Pen) .. 10.6.33D.C. Ace (SG, D, Pen) 15.7.33A.C. Three (SG, D, Pen) .. -A.C. Leader (HF Pen, D, Power) 7.4.34D.C. Premier (HF Pen, D, Pen) 31.3.34Ubique (HF Pen, D (Pen), Pen). 28.7.34Armada Mains Three (HF Pen, L;,

Pen) .. . .. 18.8.34F. J. Camm's A.C. All -Wave Silver

Souvenir Three (HF, Pen, D,Pen) .. .. 11.5.35

" All Wave " A.C. Three (D, 2LF(R.C.)) ..

A.C. 1936 Sonotone (HF Pen,17.8.35

Pen, Westector, Pen) .. .. 31.8.35

Four -valve : Blueprints, Is. each.A.C. Fury Four (SG, SG, D, Pen)A.C. Fury Four Super (SG, SG, D,

Pen) .. .

A.C. Hall -Mark (HEPen, D, Push -Pull) . .

Universal Hail -Mark (HF, Pen, D,Push-pull) _ ,

11.8.34

15.4.33

7.10.- 33

9.2.35

SUPER NETS.Battery Sets : Blueprints, Is. each.£5 Superhet (Three valve) .. -F. J. Camm's 2 -valve Superhet

(two -valve) .. 13.7.35F. J. Camm's £4 Superhet .. -Mains Sets : Blueprints, Is. each.A.C. £5 Superhet (three -valve) .. -D.C. £5 Superhet (three -salve) .. 1.12.34Universal £5 Superhet (three

valve) _F. J. Camm's A.C. £4 Superhet 4 -F. S. Camm's Universal £4 Super -

het 4 .. 11.1.36


Three -valve : Blueprints, 1s. each.Experimenter's Short-wave Three

(SG, D, Power) ..The Prefect 3 (1), 2 LF, RC and

Trans.) ..

15.9.34

8.2.36

PW36B

PW10

PW34APW35PW37

PW39PW41

PW48

FW40P3I2

PW51

PW53

PW55PW61PW62PW'64

PW11

PW17

PW34BPW34C

W46

PW18PW31

PW19

PW23PW25PW29

PW35CPW35BPW36A

PW38

PW50

PW54

rw5o

PW:20

PW3413

PW43

r.W47

PW40

PW52PW58

PW43PW42

PW44PW59

PW60

PW38A

PW30A

PWG3

PORTABLES.Three -valve : Blueprints, Is. each.F. J. Canines ELF Three -valve

Portable (HF Pen, D, Pen) .. 16.5,36 PW05


D, LF, Cl. B) PW12

MISCELLANEOUS.B.W. Converter -Adapter (1 valve) - PW4SA


Blueprints, Sd. each.Four -station Crystal Set .. - AW4271934 Crystal Set . .. - AW444150 -mile Crystal Set .. - AW450

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, 1s. each.B.B.C. Special One-valver .. - AW387Twenty -station Loud -speaker

One-valver (Class B) .. .. - AW449

Two -valve : Blueprints, 1s. each.Melody Ranger Two (D. Trans).. - AW388Full -volume Two (SG., Det., Pen) - AW392B.B.C. National Two with Lucerne

Coil (D. Trans) .. .. . - AW377ABig -power Melody Two with

Lucerne Coil (SG, Trans) .. - AW338ALucerne Minor (D. Pen) .. .. - AW426A Modern Two-Valver - .. July '36 WM409

Three -valve : Blueprints, Is. each.Class -B Three (D, Trans, Class B)New Britain's Favourite Three

(D, Trans, Class B)Home -Built Coil Three (SG, D,

Trans) -Fan and Family Three (D, Trans,

Class B) £5. 5s. S.G.3 (SG, D, Trans)1934 Ether Searcher: Baseboard

Model (SG, D, Pen) ..1934 Ether Searcher Chassis

Model (SG, D, Pen) ..Lucerne Ranger (SG, D, Trans) ..Cossor Melody Maker with Lucerne

Coils .. P.W.H. Mascot with Lucerne Coils

(D, RC, Trans) .. .Mullard Master Three with

Lucerne Coils .£5 5s. Three : De Luxe :Version

(SG, D, Trans)Lucerne Straight Three (D,

Tram) .. .All Britain Three (HF Pen, D, Pen)

Wireless League " Three (HFPen, D, Pen) , . 3.11.34

Transportable Three (SG, D, Pen) -£6 Os. Radiogram (D, RC, Trans) -Simple tune Three (SG, D, Pen).. June '33Economy -pentode Three (SG, D,

Pen) .. Oct. '33" W.M." 1934 Standard Three

(SG, D, Pen)£3 3s. Three (SO, D, Trans) .. Mar. '34Iron -core Band-pass Three (SG, D,

QP21) June '341935 £6 Os. Battery Three (SG, D,

Pen)P.T.P. Three (Pen, 13, Pen) .. June '35Certainty Three (SG, 0, Pen) .. Sept. '35Minitube Three (SG, D, Trans) .. Oct. '35All -wave Winning Three (SG, D,

Pen) Dec. '35

22.4.33

15.7.33

25.11.332.12.33

20.1.34

AW386

AW394

AW404

AW410AW412

AW417

- AW419- AW422

- AW423

- AW337A

- AW424

19.5.34 AW435

AW437AW448

AW451W31271WM318W31327

WM337

WM351WM354

WM362

WM371W31389WM393WM396

WM400

Four -valve : Blueprints, Is. 6d. each.65/. Four (SO, I), RC, Trans) .. - AW370" A.W." Ideal four (2SG, D, Pen) 16.9.33 AW4022 H.F. Four (280, D, Pen) .. - AW421Crusaders' A.V.C. 4 (2HF, D,

QP21) . . 18.8.34 AW445(Pentode and Class -73 Outputs for

above : blueprints 6d. each) .. 25.8.34 AW445ASelf-contained Four (SG, D, LF,

Class B) Aug.'33 WM331Lucerne Straight Four (SG, D, LF,

Tram) _ WM350£5 5s. Battery Four (HF, D,

2LF) Feb. '35 WM381The H.R. Four .. Mar. '35 W31384The Auto -Straight Four .. .. April '36 WM404The Request All -Waver June '36 WM407

Five -valve : Blueprints, Is. 6d. each.Super -quality Five (211F, D, RC,

Trans) . . . May '33 WM320New Class -B *Five (2SG, *I),

Class B) Nov. '33 WM340Class -B Quadradyne (2SG, D, LF,

Class B) - .. Dec. '33 WM3441935 Super Five (Battery Super -

het) .. - W31379

These blueprints are full size. Copies of appro-priate issues containing descriptions of these setscan in most cases be obtained as follows :-" Practical Wireless" at 4d., " Amateur Wire-less" at 4d., " Practical Mechanics" at 71d., and" Wireless Magazine" at 1/3d., post paid. Indexletters " P.W." refer to " Practical Wireless"sets, " P.M." to " Practical Mechanics" sets," A.W." refer to " Amateur Wireless" sets, and" W.M." to " Wireless Magazine" sets. Send(preferably) a postal order (stamps over sixpenceunacceptable) to " Practical and Amateur Wire-less" Blueprint Dept., Geo. Newnes, Ltd., 8-11,


Mains Operated.Two -valve : Blueprints, 1s. each.Consoelectric Two (D, Pen) A.C.. 23.9.33Economy A.C. Two (D.Trans) A.C. -Unicorn A.C./D.C. Two (D, Pen) . Sept. '35Three -valve : Blueprints, 1s. each.Home -lover's New All -electric

Three (SG, D, Trans) A.C. - AW383S.O. Three (SG, D, Pen) A.C. - AW390A.C. Triodyne (SG, D, Pen) A.C. 19,8.33 AW399A.C. Pentaquester (HF Pen, D,

Pen) A.C. .. 23.6.34 AW430Mantovani A.C. Three (HF Pen,

D, Pen) A.C. - WM371£15 15s. 1936 A.C. Radiogram

(HF, D, Pen) .. Jan. '36 WM401

Four -valve : Blueprints, 1s. 6d. each.All Metal Four (2 SG, D, Pen) .. July '33 WM329Harris Jubilee Radiogram .. May '35 WM386

SUPERHETS.Battery Sets : Blueprints, 1s. 6d. each.Modern Super Senior .. - WM375Varsity Four .. .. Oct. '35 WM393

Mains Sets : Blueprints, 1s. 6d. each.1934 A.C. Century Super A.C. .. 10.3.34Heptode Super Three A.C. .. May '34" W.M." Radiogram Super A.C...1935 A.C. Stenode.. Apt. '35

PORTABLES.Four -valve : Blueprints, 1s. 6d. each.Midget Class B Portable (SG, D,

LF Class B) . 20,5.33 AW389Holiday Portable (SG, D,

Class B) 1.7.33 AW393Family Portable (HF, D, RC,

Trans) .. . 22.9.34 AW447Two H.F. Portable (2 SG, D.,

QP21) June '34 WM363Tyers Portable (SG, D, 2 Trans) . Aug. '34 W31367

SHORT -WAVERS --Battery Operated.One valve : Blueprints, 1s. each.S.W. One -valve converter (Price ed.) -S.W. One -valve for America .. -Roma Short -waverTwo -valve : Blueprints, 1s. each.Ultra -short Battery Two (SG det,

Pen) .. . Feb. '36 WM402Home-made Coil Two (D, Pen) .. - AW440

Three -valve : Blueprints, is. each.World -ranger Short-wave 3 (D,

RC, Tram) .. - AW355Experimenter's 5 -metre Set (D,

Trans, Super-regen) .. 30.6.34 AW438Experimenter's Short -waver . .Jan. 19, '35 AW463The Carrier Short -waver .. July '35 WM390

Four -valve : Blueprints, 1s. 6d. each.A.W. Short-wave World Beater

(HF, Pen, D, RC, Trans) - AW436Empire Short -waver (SG, D, RC,

Trans) .. - WM313Standard Four -valve Short -waver Mar. '35 W31333

Superhet : Blueprint, is. ad.Simplified Short-wave Super .. Nov. '35 W11397

Mains Operated.Two -valve : Blueprints, 1s. each.Two -valve Mains Short -waver (D,

Pen) A.C.W.M." Band -spread Shortwaver(D. Pen) A.C./D.C. . Aug. '34

"W.M." Long -wave Converter ..Three -valve : Blueprint, 1s.Einigrator (SO, D, Pen) A.C. -Four -valve : Blueprint, 1s. 6d.Standard Four -valve A.C. Short -

waver (SG, D, RC, Trans) .. Aug. '35 WM391

MISCELLANEOUS.Enthusiast's Power Amplifier (1/6) June '35 WM387Listener's 5 -watt A.C. Amplifier

(1/6) . Sept. '35 WM392Radio Unit (2v.) for WM392 (1s.). Nov. '35 WM399Harris Electrogram (battery am-

plifier) '35 WM339De -Luxe Concert

........Dec.*A.C.Electro-

gram .. Mar. '36 W51403New style Short-wave Adapter

(1s.) June '35 WM388Trickle Charger (6d.) .. Jan. 5,'35 AW462Short-wave Adapter .. Dec.1, '34 AW456Superhet Converter .. Dec. 1, '34 AW457B.L.D. L.C. Short -Wave Converter

Is.) May '36 WM495Wilson Tone Master (1s.) .. June '36 W31406The W.M. A.C. Short -Wave Con-" verter (1s.) July '36 WM493

AW403WM286WM394

AW425WM359WM366WM385

AW:1929AW429AW4V

AW453

WM368WM360

WM352


OlivERIESNW/RIES

Automatic Bias and the Monitor" I wish to add automatic grid bias to the

Monitor first stage, and want to know ifthis is advisable. Also could you tell mewhat type of mains transformer and valverectifier are required for making an A.C.eliminator for the Monitor? "-G. B. (Ley-tonstone, E.11).

TO include automatic bias the H.T.negative lead (lead No. 39) should be

removed from the E terminal on the L.F.transformer. From this latter point oneside of a 700 ohms resistance should beconnected, and the H.T. lead should thenbe attached to the other end of the resist-ance. A by-pass condenser (2 mfd.) shouldthen be joined across the resistance. Forthe mains unit we would suggest a HeayberdType W20 transformer in conjunction withan H.T.5 Westinghouse rectifier.

Modifying a Meter" I have a good voltmeter which reads

from 0 to 150 volts. How can I convert itso that it will read up to 5 volts ? Also,as each degree on the scale means a rise of6 volts, what will each degree mean when themeter has been converted ? "-J. B. (Eding-ton, Nr. Bridgwater).1"HE meter is wound to a certain resist-

ance,1 and when a voltage of 150 isapplied to the meter the resultant currentflowing through the windings just turns thecoil sufficient to carry the pointer to theend of the scale. Consequently, whenapplying only 5 volts, the current will betoo small to deflect the needle to the end ofthe scale or to give reasonable deflection.If, therefore, you wish the needle to givea full scale deflection at only 5 volts, youmust increase the current flowing throughit at that voltage, and this can only be doneby modifying the internal construction, andwe do not advise this. A meter may easilybe modified to give a higher reading by theuse of external resistances, but it cannotbe modified to give a reduced readingwithout getting to the inside of the meter,and this procedure is not advisable unlessyou are fully aware of the changes you

make.

Band -spread Tuning" I am making a three -valve short-wave

set with band -spread tuning and enclose mylayout herewith. I have only one short-wave condenser at the moment, and shouldlike your recommendation regarding theextra band -spread condenser. I have notyet bought this component and am not veryparticular regarding price. Can you suggestany other improvements to the set? "-V. C. 0. (Barking).

WHILST an ordinary condenser couldbe used for the purpose you would

find tuning slightly complicated owing to thevarious combinations of the two condenserswhich can be obtained. A well -calibrateddial firmly locked to the spindle willavoid this, but as you have not obtainedthe component yet we suggest that youconsider the special bandspread tuning

outfit supplied by Messrs. Strattonand Co. This consists of a .00015mfd. condenser with a dividingplate divided into ten sections.

These are located by means of aspring -loaded ball and a dial is providedwith the condenser and is marked from 0 to10. A small capacity trimmer is providedwith a 9 to 1 reduction drive dial, and thiscombination greatly simplifies tuning asvarious settings are easily re -found dueto the two dials and the relative capacitiesof the two components. The price is12s. 6d. the pair, 6s. for the tank condenser,and 6s. 6d. for the bandspread condenser.

rRULES

We wish to draw the reader's attention to thefact that the Queries Service is intended onlyfor the solution of problems or difficulties

1 arising from the construction of receiversdescribed in our pages, from articles appearingin our pages, or on general wireless matters.

1 We regret that we cannot, for obvious reasons-

II (1) Supply circuit diagrams of completemulti -valve receivers.

NW'

(2) Suggest alterations or modifications ofreceivers described in our contem-poraries.

(3) Suggest alterations or modifications to, I

ings which are sent to us should bear the

commercial receivers.

(4) Answer queries over the telephone.

(5) Grant interviews to quer ists.

Please note also, that queries must be limitedto two per reader, and all sketches and draw -

name and address of the sender.

It a postal reply is desired, a stamped -addressed envelopemost be enclosed. Send your queries to the Editor,PRACTICAL AND AMATEUR WIRELESS, Ceo. Newnes,Ltd., 8-11, Southampton Street, Strand, London, W.C.2.

i11.1=0.1

Eureka Resistance Wire" I have a bobbin of Eureka resistance

wire handy, but the only data which I cannow find is the diameter which is .006. Iwant to wind some resistances for experi-mental work and should be glad if you couldgive me any details concerning the resistanceof this particular gauge of wire and anyother useful data."-G. B. (Bristol).

THE wire would be 38 S.W.G., having aresistance of 23.8 ohms per yard.

The length per ohm of this particular gaugeis 1.5 inches, which is a very convenientlength for winding various types of resist-ance, and it will, of course, wind 118 turnsto the inch approximately if it is double silkcovered.

Mixer -fader Control Box" I am building the public-address adjunct

described in your issue dated July 25th,but I am only going to use two input circuitsfor the moment. These will be pick-up andmicrophone. Later on I may add a secondpick-up input, but then the same difficultyas I now experience will arise. I want toset both mike and pick-up to a zero positionso that neither will be heard, or so that an

equal volume will be obtained from each.It will be difficult to juggle with eachpotentiometer to get the necessary balance,and I wondered whether any fixed resistorcould be brought into parallel by means ofa switch to do the trick. What should thevalue be, if this idea will work ? "-B. L. S. (Dover).IF you are only going to employ a double

input circuit, the simplest idea is todispense with the two separate potentio-meters mentioned in the text and to usein their place one of the Dubilier Fadovercontrols. This consists of two equalelements and a central position is indicatedby a locating stud which may easily befelt when the control is operated. Onehalf of the control would then be joinedacross the pick-up and the other half acrossthe mike, providing a smooth changefrom one to the other, with the " off "position at the centre. Additional circuitscould be similarly wired.

Quenching Coils" I am trying out some short-wave circuits

and should like to try the one -valve super -regenerative arrangement shown in yourShort Wave Section for July 4th. Allvalues which matter are given on thisdiagram, but no details of the quenchingcoils are shown. Could you give me thisinformation, please ? "-S. M. (Newcastle).

THE simplest way of making up thecoils is to obtain three 2in. diameter

discs of ebonite and mount these on a shortlength of studding or a long bolt (brass, notiron). They should be separated bytwo 1 in. diameter discs one -eighth of aninch thick. The two bobbins thus providedshould then be wound with 36 S.W.G.enamelled wire, 500 to 600 turns beingemployed. The frequency of the quenchingoscillation may be adjusted by means of theparallel condensers. Alternatively, you canobtain a ready-made quenching coil unit,although these components do not seem tobe readily obtainable to -day.

Metallised Valves and Chassis" I have been trying to metallise my

valves and the chassis, and although fairresults have been obtained with tinfoilshellacked in position, it is not perfect. Canyou tell me how to carry out the processsatisfactorily at home ? I do not want touse a sheet of foil over the baseboard as Ifind that this tears and interrupts the con-tinuity."-F. T. (Edgware).

THERE is no satisfactory way of carryingout the process of metallising valves or

other components at home. A chassismay be covered with aluminium or copperfoil, or even a thin sheet of metal with satis-factory results, but a valve cannot be socovered. Foil provides a partial degreeof screening, but when using shellac orsimilar material for sticking this may runbetween adjacent layers or in the jointsand insulate them, thus breaking thecontinuity. The process used on valvesand the chassis specified for our receiversis intricate, and the material used is zinc.This is melted in a crucible, and a Bunsentype flame keeps the metal molten whilstit is sprayed upon the component by meansof compressed air at a pressure of 60-75pounds per square inch. This air is pre-heated and the metal is atomised, theresulting layer generally being about fourthousandths of an inch thick.

r 1.11.01.

The coupon on cover iii must beattached to every query.

1....0.410.111111/1.*.04/00,0411.0411111.100.0"


Miscellaneous AdvertisementsAdvertisements are accepted for thesecolumns at the rate of 3c1. per word. Wordsin black face and/or capitals are chargeddouble this rate (minimum charge 3/- perparagraph). Display lines are charged at6/- per line. All advertisements must beprepaid. All communications should beaddressed to the Advertisement 'Manager," Practical and Amateur Wireless,"8, Southampton Street, Strand, London.



RADIOMART (G5NI)SHORT-WAVE SPECIALISTS


RADIOMART. Utility 2 -gang uniknob and 'dial,3/11, 1,500 vt. Tubular condensers, 6d. Helsby

electrolytics 8 mf. 500, 2/11, 4 x 4 mf., 1/6, 25 rat,25 V., 1/-, etc.

ADIOMART. Smoothing chokes, 20 by 120 ma.,00 a., 2/11 ; 40 ma., 1/11. Telsen Ace

transformers,1 1/11m. Radiogrands, RG48, 2/5. BTHspeaker, 2/11.

RADIOMART. Varley iron -cored, 10/6. Bifocaldual -range coils. Very selective, 2/11; matched

pair, 5/3.RADIOMART. Pushback wire 6 yds. 6d., heavy

9d. ; 2 gross solder tags, Cd. Resincored solder,Oft., 6d.

RADIOMART, Centralab pots, all sizes, 1/5;switched, 2/-. Tubular glass fuses, 2d.

RADIOMART. Igranic midget jacks, 3d. Milliam-meters, 25 ma. upwards, 5/9 ; super 6/9.

RADIOMART. Telsen H.F. chokes, 1/11 screened1/11. Utility 1936 SL wavelength dials, 3/11.

RADIOMART. Lissen 3 -gang superhet kit coils,two I.F.'s ganged condenser, ditto Bandpass,

ditto 2 -gang all wave, 10/- kit.RADIOMART. Traders' monster bargain parcels,

value £4/10/0 for 10/-; also 5/- parcels.RADIOMART. Famous continental A.C. valves,

4/6. American Durtron, etc. All types,, 3/6.Battery from 2/3.

RADIOMART. Utility 8/6, microdlsc dials, 3/11.Radiophone .00016 short-wave condensers, 3/6.

Series gap twin, 3/9.RADIOMART. Ceramic all brass microvariables,

15 mmfd., 1/4. 40 mmfd., 1/7. 100 mmfd., 1/10.Short-wave HFC., 9d.

ADIOMART. Orders 5/- post free. Get our bar -1 -X gain catalogues. General, 14d. Short-wave, nd.44, Holloway Road, Birmingham. Tel.: MID 3254.


VAUXHALL UTILITIES, 163a, Strand, W.C.2.Over Denny's the Booksellers. Temple Bar

9338.

CONVERSION UNITS for operating D.C. Receiversfrom A.C. Mains, improved type, 120 watts

output, at 12/10/0. Send for our comprehensive list ofspeakers, Resistances and other components.

WARD, 46, Farringdon Street, London, E.C.4.Telephone: Holborn 9703.

TRANSCEIVERS 1, 2 and 3 Valve Battery_Models£3, £5 2s. fld., £6 7s. 6d. AC Mains, 4 Valve, £9.,

300 mile range, complete with valves and cabinets.Write for illustrated leaflet.

2 i/ 555 Meter 5 band, 5 valve communications receiver.ACIDC. MC Speaker, Bandspread,'ete., £9 17s. 6d.

ALL goods guaranteed satisfaction or money re-funded.-Radiographic Ltd., 66, Osborne Street,

Glasgow, C.1.

ALCO ELIMINATORS AND CHARGERS. 4 H.T.taps, 120/150v., 20/30 ma., 18/-, with charger,

25/-; charger alone, 7/6; amp., 11/-. Year's guaran-tee, details free.-P. and D. Radio Service, 1, GoodingeRoad, N.7.

BANKRUPT Bargains. List free. G.E.C. batterycompact, 3v. with valves and M.C., 42/6. Alba

3v. H.F. pentode sets with BVA valves, M.C., andbatteries, 67/6. Ekco 15 gn. car radios, 12v., 17/10/0.Cossor D.C. 3v. M.C. BVA valves, 77/6. Ultra 13 gn.1936 D.C. superhet, 7 gns. Also Pilot and Fergusonallwave. Many other receivers and large stock replace-ment valves and components. All new goods.-Butlin, 6, Stanford Avenue, Brighton.

MISCELLANEOUSTELEVISION.-Newnes Television and Short-

wave Handbook, by F. I. Camm, deals authori-tatively with Scanning Systems (Drums, MirrorScrews, Discs, etc.), Neon Lamps, The Cathode -RayOscillograph, How to Build Short-wave and Ultra -short -wave Receivers. Fully illustrated. 3s. 6d. net.From your bookseller.-George Newnes, Ltd., 8-11,Southampton Street, Strand, London, W.C4.



S.W.4. (Macaulay 2381 1and 165 and 165a, Fleet St., E.C.4 (next to Andertons

Hotel). (Central 2833.)NOW READY ! Send 4d. in stamps for NEWILLUSTRATED GIANT CATALOGUE AND VALVE

LIST.SHORT WAVES.

S HORT-WAVE COILS 4 to 6 -pin types. 13-26,22-47, 41-94, 78-170 metres, 1/9 each with

circuit. Special set of 3 S.W. Coils, 14-150 metres,4/-, with circuit. Premier 3 -band S.W. Coil,11.25, 19-43, 38-86 metres. Simplifies S.W. re-ceiver construction, suitable any type circuit, 2/-.

COILFORMERS, in finest plastic materials,

liin, low -loss ribbed 4- or 6 -pin, 1/- each.ri3ONDENSERS, super ceramic, S.L.F. .00016,10 .0001, 2/9 each; double-spaced .000015,.000025 ,.00005, 3/- each. All brass with integralslow-motion .00015 tuning, 3/9 ; .00015 reaction,2/9.SHORT-WAVE KIT for 1 valve receiver or

adaptor, complete with chassis, 3 roils 14-150metres, condensers, circuit diagram and all parts,12/6. VALVE GIVEN FREE.2 -VALVE S.W. KIT, complete with valves, 19/6.

!a -VALVE S.W. KIT, Det. and Pen., completew with valves, 40/-.RAND PASS KIT, 14/6 the lot. Lissen 3 -gangag coil unit. Utility 3 -gang condenser anddisc drive, 4 valve -holders, chassis and wiringdiagram.SPEAKERS, K.B. 8" P.M.s 9/6, Goodman

P.M.s, 9/6.MAINS TRANSFORMERS. Premier wire -end

type with screened primaries.H.T.8 & 9 or H.T.10 with 4v. 4a. C.T. and 4v. la.C.T., 8/8.250-250v. 60 m.a., 4v. la., 4v. 2a. and 4v. 4a., allC.T., 8/6.350-350v. 120 m.a., 4v. la., 4v. 2a. and 4v. 4a.,all C.T., 19/6.500-500v. 150 ma., 4v. 2-3a., 4v. 2-3a., 4v. 2-3a.,4v. 3-4a., all C.T.,19/6.Any of these transformers with engraved paneland N.P. terminals, 1/0 extra.AUTO TRANSFORMERS, step up or down,

60 watts, 7/6, 100 watts, 10/-.MA I N8 VALVES, famous Europa 4v. A.C.

types, 4/6 each. ILL., L., S.G., Var.-Mu-S.G., H.F.-Pens., Var.-Mu.-H.F. Pens, 1, 3,and 4 -watt A.C. directly -heated output Pentodes.Full -wave rectifiers, 250 v. 60 ma. A.C./D.C.types, 20 -volt .18 amp. B.G., Var.-Mu-S.G., H.,H.L., and Power.Following Types all 5/6 each. Full -wave rectifiers350v. 120 m.a. and 500 v. 120 ma. 2i watt in-directly -heated Pentodes. Frequency Changers.Octodes and Heptodes.B ATT E R Y VALVES. 2 -volts, B.F., L.F., 2/3.

Power, Super -Power, 2/9. S.G., Var.-Ma-S.G., 4 or 5 -pin Pentodes, H.F. Pens., V.-Mu-II.F.Pens., 5/-. Claes B, 3/6.AMERICAN VALVES. Genuine American

DUOTRON, all types, 3/6 each. Hytronsuper quality, 3 months' guarantee, all types. 6/6.LMEN 2 -Gang All -Wave Coils, cover 12/2,000

metres in 4 Bands. Integral switching, withcircuit, 12/6.3 WATT A.C. Amplifier 2 -Stage for mike or

pick-up. Complete Kit of Parts with3 valves, 40/-.MILLIAMMETERS, moving -iron flush 2r,

all ranges from 0-10, 5/9. Visual tuning,6 or 12 ma., 5/-. Moving coil meters, 2-1"" 0-1 m.a.,18/6; 3}" 0-1 ma., 22/6. Multipliers, 1/- each.Westinghouse meter rectifiers, 17/6 each.ELECTROLYTIC8. U.S.A. 4, 8 or 12 mfd. 520 v.16. peak, 1/9 each. Dubilier, 4 or 8 mfd. 500 v.,3/- ; 50 mfd. 50 v., 1/9 ; 12 mfd. 20 v., 6d.; 25 mfd.25 v., 1/-. T.C.C. 4 or 8 mfd. 650 v., 4/- i 15 mfd.50 or 100 v., 1/-; 50 mfd. 12 v., 1/-.Paper Condensers. W.E., 250v. working 4 mid., 2/-,2 mfd. 1/-, 1 mfd. 6d. ; 350 v. working 4 mfd. 2/6.2 mfd. 1/6, Dubilier 600 v. working 4 mfd. 4/-;800 v. 4 mfd. 6/-; 2 mfd. 750 v. 3/.Wego 450 v. working 1 mfd. 1/-, 2 mfd. 1/9, 4 mfd.3/- 700 v. working 2 mfd. 2/-, 4 mfd. 3/6; 1,650 v.working 1 mfd. 3/6, 2 mfd. 5/6.

TRANSFORMERS latest type Telsen R.G.4(list, 12/6), 2/9. Lissen Hypernik Q.P.P.

(list, 12/6), 3/6.ELIMINATOR KITS for A.C. mains. 120 v.

20 ma. or 150 v. 25 m.a., 10/-, tappedS.G. det. and output. Complete Kit with long -lifevalve rectifier (replacement cost only 2/-).LINEN ALL -ELECTRIC A.C.4, S. Grid. Det.,

Pen. and Rectifier, M.C. Speaker. (List,£0.9.0.). Our price, 65/-.Potentiometers by well-known makers. All valuesup to 1 meg., 2/- : with switch, 2/6.




POST PAID.PEAKERS.-Celestion Soundex Permanent Magnet,

1.3 10/-; Telsen Permanent Magnet with ten -ratiotransformer, 12/6; Blue Spot 99P.M. ExtensionSpeaker, 20/-; Telsen Loud Speaker Unit, 2/6 ; allnew and boxed.

RECEIVERS.-G.E.C. A.C. D.C. Mains Three -valvesets. Complete, with 3 Osram Valves, in ex-

quisite Bakelite cabinet with Osram M.C. Speaker.Ready to plug in to any mains. Fully guaranteed.New, in sealed cartons, £3/5 (list 17/15).

G.E.C. Colpact 3 -valve Battery Set s complete with3 Osram valves, moving coil P.M. Speaker in

attractive Bakelite cabinet. makers' 1936 series inoriginal sealed carton, 50/- (List 15/10/0).


Speaker. Three Mullard Pentode valves in beautifulwalnut cabinet. Brand new, in sealed cartons, 14/10(List 18/8). -

MELSEN A.C. D.C. MULTIMETERS (latest 1936type). -5 -range for every conceivable test for

radio and domestic electrical appliaqces, 8/6 each.COILS.-TELSEN (1936). Iron-dored Coils, Type

W349, midget size, 4/-; type W478 (twin), 9/-pair; type W477 (triple), 16/-; type W476 (triplesuperhet selector and oscillator), 16/- set. All GangedCoils are Mounted on Base with switch. I.F. Trans-former Coils W482, 5/-; Telsen Dual Range Coil withvariable series condenser W76, 4/-; Varley SquarePeak Coils BPS, 2/-.

ELIMINATORS.-Regentone (1936) Type. W5awith trickle charger, 37/6; Type WIa (less

trickle charger), 32/6.MICROPHONES.-Ace (P.O.) Microphones, com-

plete with transformer, perfect with any typeof receiver, 4/6.

TRU-OHM RESISTANCES. -1 Watt. Wire endscolour coded and marked; 36 assorted capacities

on card, 6/-.AAMERICAN VALVES.-A full range of valves for

all American sets at 7/- each. Brand new,guaranteed.

SOUTHERN RADIO BRANCHES. -271/275, HighRoad, Willesden Green, N. W.10 ; 46, Lisle Street,

W.C.2. All mail orders to 323, Euston Rd., N.W.1.OUTHERN RADIO, 323, Euston Rd., London,



W.C.1. Tel.: Holborn 4631.

MISCELLANEOUS

SHORT WAVE on a crystal set. Full buildinginstructions and crystal, 1/2 post paid.-Radiomail,Tanworth-in-Arden, Warwickshire.

3S. EACH any popular type of American valves.90 days guarantee. Orders 10/- or over Carriage

Paid. Satisfaction or Money Refunded immediately.RADIOGRAPHIC LIMITED, 66, OSBORNESTREET, GLASGOW, C.1.

REVIEWED August 8th. New Theory Book. Postfree ls. ld.-D'Arcy Ford, 15, Gandy Street,

Exeter.

YOUR Cigarette Lighter repaired. Is. 6d. includesreturn postage.-Scaling, 47, Abbey Road,

Llandudno.


LJULBERT for Quality Surplus Speakers. AllMusic Lovers should write for List of amazing

bargains. Prices from 8/6 brand new. Made by bestknown British maker.-Hulbert, 6, Conduit Street,W.1.


Brand new stock with six months' guarantee. 2 volt,Detector, 2/3, Power 2/9, Screen Grid, Pentode, H.F.Pentode, 5/-. The following American type valves,fully guaranteed, at 5/6 each: No. 80, 42, 43, 57,58, 77, 78, 6C6, 6D6, 25Y5, 25Z5. Write for otherprices to : Dulci Electrical Co., Ltd., 7, LizardStreet, London, E.C.1.

CLARION VALVES.-All brand new, battery types2 -volt, H.2, H.L.2, L.P.2, 1/9; super power

P2, 2/6; screens and L.F. pentodes, 3/9; A.C. mains4 -volt, 1 -amp., general purpose, 3/3; power, 4/-;screens and L.F. pentodes, 4/6; full wave rectifiers,3/6; postage paid, cash with order, or C.O.D. over10/ -.--Clarion Valves, Dept. 2, 885, Tyburn Road,Erdington, Birmingham,

August 22nd, 1936 PRACTICAL AND AMATEUR WIRELESS iii

MISCELLANEOUS

" MEWNES TOURIST ATLAS of Great Britain andI NI Route Guide." Edited by John Bartholomew

& Son, Ltd., 120 pages of fully coloured contour mapsfor the whole of England, Scotland, Ireland andChannel Islands, with Index to the principal Motoringand Cycling centres and distances. 2s. 6d. from allBooksellers.-George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2.

VISITORS TO LONDON should get Newnes HandyPocket Atlas and Street Guide to London. Edited

by John Bartholomew & Son, Ltd., 18 coloured Maps,General Index to Streets and Railway Stations. 2s.from all booksellers.-George Newnes, Ltd., 8-11,Southampton Street, Strand, London, W.C.2.

WORKING MODELS and How to Make Them."Edited by F. J. Camm, 3s. 6d.-This Book

will appeal to all who are handy with tools. Containscomplete instructions for the making of every kind ofworking model. Each model has been actually con-structed in accordance with the details given and sub-jected to stringent tests. The instructions anddiagrams are so clear that even the most elaboratemodel can be built without fear of failure. Obtainableat all Booksellers and Newsagents. -Geo. Newnes,Ltd., 8-11, Southampton Street, Strand, London,W.C.2.

"WIRELESS FOR THE MAN -IN -THE -MOON,"by Coulumbus and Decibel, 2s. 6d. net.-

Writing about the book the "Midland Daily Tele-graph " says : " It is both good fun and sound theory."-At all Booksellers and Libraries, or from GeorgeNewnes, Ltd., 8-11, Southampton Street, Strand,London, W.C.2.

"'THE OUTLINE OF WIRELESS," by RalphStranger. Fifth edition, 8s. 6d. net.-This

book, which covers the subject from A to Z, is to berecommended to all who desire to master the theoryof Modern Wireless. At all Booksellers and News-agents.-George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2.

EOM THE RADIO ENTHUSIAST-" The WirelessF Constructor's Encyclopaedia," by F. J. Carom(Editor of "Practical and Amateur Wireless "),third edition. Compiled by one of the most accom-plished designers and writers on the practical side ofWireless, it covers the whole field. A veritable Treasuryof Wireless Knowledge. Price 5s., from all Booksellersand Newsagents.-George Newnes, Ltd., 8-11, South-ampton Street, Strand, London, W.C.2.

ADICTIONARY OF WIRELESS TERMS, byRalph Stranger. A Wireless Work of Reference

that should be on the bookshelf of every keen amateur.Compiled by a master of lucidity, it gives the meaningsof all Technical terms in general use. Price 2s. 6d.from all Booksellers and Newsagents.-George Newnes,Ltd., 8-11, Southampton1Street,Strand, London, W.C.2.

FIFTY TESTED WIRELESS CIRCUITS, by F. J.Camm, 2s. 6d.-This handbook contains every

modern circuit, complete with instructions for assem-bling, component values, and notes on operation.Obtainable at all Booksellers and Newsagents.-GeorgeNewnes, Ltd., 8-11, Southampton Street, Strand,London, W.C.2.

MORE THRILLING THAN FICTION.-NewnesWide World Library contains the finest true -life

travel and adventure books, great literature and ex-hilarating reading. Each 2s. 6d. net from all Book-sellers.-George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2.

PERPLEXITIESand TANTALISERS. - "The

Strand Problems Book " is the finest collection ofpuzzles of all kinds ever assembled, mathematical,geographical, literary-acrostics and codes, by W. T.Williams (Tantalus) and G. H. Savage, Only 2s. 6d.net from all Booksellers.-George Newnes, Ltd.,8-11, Southampton Street, Strand, London, W.C.2.

rVERYMAN'S WIRELESS BOOK, by F. J. Camm,E., 3s. 6d. net. An invaluable book of referenceexplaining the operation, upkeep and overhaul of alltypes of wireless receiver. 200 illustrations. Fromall Booksellers and Newsagents.-George Newnes,Ltd., 8-11, Southampton Street, Strand, London,W.C.2.

110 ILLUSTRATIONSNEW I2 PAGEBARGAIN LIST

f ant Out f FREE List "N," It givesdetails of a host of electrical bargains.

PARCELS of experimental odd coils,magnets, wire, chokes, con-densers, switches, terminals,etc., post free: 10 lbs., TI-;7 lbs., 5/.. 1,000 otherBargains in New Sale List " N."


PhorL C ntrol 4611

LOUDSPEAKER REPAIRS

REPAIRS to Moving Coil Speakers, Cones and Coilsfitted or rewound. Fields altered. Prices

Quoted including Eliminators, Loud -speakers Re-paired, 4/-. L.F. and Speech Transformers, 4/- postFree. Trade invited. Guaranteed. Satisfaction.Prompt Service. Estimates Free. L. S. Repair Ser-vice, 6, Balbam Grove, London, S.W.12. Battersea1321.

ADVERTISEMENT INDEXPage

Automatic Coil Winder .. .. 579Belling & Lee, Ltd. .. .. Inside Back CoverBritish Institute of Engineering Technology 589Electradix Radios .. .. Inside Back CoverExide . Back CoverInternational Correspondence Schools .. 590London Radio Supply Co... .. 589Peto-Scott Co., Ltd... .. 589Premier Supply Stores .. 5%Telegraph Condenser Co., Ltd. .. .. 593Varley, Ltd. .. .. Inside Back CoverWestinghouse Brake & Signal Co., Ltd. .. 579

THE PRACTICAL MOTORIST'S ENCYCLOP/E-DIA, by F. J. Camm, 3s. 6d. net. A lucid

exposition of the principles, upkeep and repair ofevery part of the car. 442 illustrations. From book-sellers everywhere.-George Newnes, Ltd., 8-11,Southampton Street, Strand, London, W.C.2.

FREE ADVICE BUREAU 1

COUPONThis coupon is available until August 29, !.

1936, and must be attached to all letters con-taining queries.

i PRACTICAL AND AMATEUR WIRELESS, I22/8/36. i

,5614',40`r4 Nt'

1,-0,.st%stootsccv-

This new two-colour publication contains 150illustrations, Including 75 blue prints of curves,diagrams, circuits, and constructional detailsand specification of every part, radio andelectrical spares and connections. A mine ofinformation. This publication is of particularvalue to Radio engineers, designers, and thoseengaged in any section of the Radio Industryas well as to every amateur constructor.

BELLING -LEEFOR EVERY RADIO CONNECTION

`"otax''°i's,03,1t,

SEND THIS COUPON TO -DAY

Belling & Lee Ltd., Cambridge Arterial Road, Enfield, Middx.

(Strike out item not required.)

I enclose 6d. for new book, " Radio & Electrical Accessories,"

Please send, free, "Radio Connections" folder."

Name

Address

W. 42.8 30_1

'FOREMOST AS PIONEERSOn Stand No. 95, at Radiolympia, you will findan interesting range of reliable wireless componentsmade by Varley, Will you pay us a visit ?

iv PRACTICAL AND AMATEUR WIRELESS August 22nd, 1936

R.175

THE TENDENCY IN BATTERY SETS

What analysis showsA recent analysis of the L.T. consumption of 280 present-day battery sets shows this result

0.7% with L.T. consumption under 0.3 amperes7.1% with L.T. consumption of 0.3 to 0.4 amperes

67.3% with L.T. consumption of 0.4 to 0.6 amperes22.3% with L.T. consumption of 0.6 to 1.0 amperes2.6% with L.T. consumption over 1.0 amperes

It will be seen that over 90% consume0.4 amperes or more. It shows thatmodern battery sets consume moreL.T. current. This is owing to the useof more valves and of illuminated dials.That fact is highly important. It meansthat the popular thick -plate type ofbattery, while being excellent for smallsets, is not suitable for the majorityof modern sets.This type of battery is designed forslow discharge and infrequent re-

charging, and if it has to be rechargedmore frequently than once a fortnightits life will be shortened.Moreover, it will not give the mosteconomical service, as its full ratedcapacity will not be obtained.To meet these changed conditionsExide have pro-duced a new typeof multi -plate bat-tery called theExide 'llycap'which gives itsfull rated capacitya t comparatively

high discharge rates and so lastslonger on each charge. =Listenersobtain from 3 5 % to 90% more listen-ing hours on each charge, and thisreduction in the frequency of charging,allied to the robust nature of themulti -plate assembly, considerablyimproves the durability of the battery.Incidentally, it can be recharged in halfthe time required for thick platebatteries.Operated under the conditions forwhich it was designed, it will beobvious that the Exide flycap' effectsconsiderable economies in the costof listening.Like the Exide t D' type battery, it hasthe invaluable Exide Indicator, whichtells you in time when to recharge.

Sizes and Prices of Exide ' Hycap' Batteries

Type Voltage! Capacity inampere hours atthe 20 hr. rate

Price(uncharged)

OCG3 - C 2 1 5 8/6

GFG 4 - C 2 24 I 0 / 6

GKG5 - C 2 36 1 2/ 6

CZG6 - C 2 60 15 / 6

Obtainable from_ Exide Service Stations and all reputable dealers.

EXIDE BATTERIES EXIDE WORKS CLIFTON JUNCTION NEAR MANCHESTER ALSO AT LONDON

MANCHESTER BIRMINGHAM BRISTOL GLASGOW DUBLIN AND BELFAST

Published every Wednesday by GEORGE NEWNES, LIMITED, 8-11, Southampton Street, Strand, London, W.C.2, and Printed In Great 'Britain by THE NEWNES diPEARSON PRINTING CO., LTD., ]Ixmoor Street, London, W.10. Sole Agents for Australia and New Zealand : GORDON & GOTCH, LTD. South Africa : CENTRALNEWS AGENCY, LTD. Practical and Amateur Wireless can be sent to any part of the World, post free, for 17s. 8d. per annum; six months, 8s. 10d.Registered at the General Post Office as a newspaper and for the Canadian Magazine Post.

Practi,m1 and Amateur Wireless, August 29th, 1936.

GREATLY ENLARGED NUMBER ! COMPLETE GUIDE TO THE SHOW

EVERYWEDNESDAY

Vol. 8. No. 208.August 29th, 1933.

2.5"W.B: SPEAKERS AS PRIZES!COMPLETE ILLUSTRATED GUIDE TO THE SHOW.CONSTRUCTIONAL DETAILS OF 3 RECEIVERS.PACKED WITH ARTICLES BY FAMOUS EXPERTS.

1937 STENTORIAN" A MARKED ADVANCE ON PREVIOUS MODELS

Says Mr. F. J. Camm


HERE ARE SOME OF THE MAIN FEATURES -

A full range of Osram Valves asapplied to wireless receivers.

Valves for short wave receivers.

Tuning devices.

A large working model indicating theoperation of a Cathode Ray Tube

which shows the linking up of elec-tronic action with mechanicalanalogy.

Valves for Electro-Medical uses.

Valves for laboratory measurements.

Valves suitable for Television recep-tion.

Cooled Anode Valves and someindustrial applications.

Advt. of the General Electric Co., Ltd., Head Office : Magnet House, Kingsway, London, W. C.2.

August 29th, 1936

IFIULILEIR

in your radio


I. Patented Double Grease -Cup Terminals preventacid corrosion, and ensure constant goodcontact.

2. Indestructible Ebonite Separators prolong thelife of the accumulator.

3. Non -interchangeable Coloured Terminals withRaised Polarity Signs make wrong connectionsimpossible.

4. 3 " Mammoth" Full Capacity Plates giveextra capacity.

5. New Filling Vents and the heavy mouldedglass containers give strength and distinctiveappearance ; fitted with Charge Indicator.

AND PRICES ARE REDUCED

BATTERIES BY

411:rjThe hall mark of qualilqLLEIR

LDGHREDUCED

PRICE

9/3

Service Agents throughout the CountryThe Fuller Accumulator Co.(t926) Ltd, Chadwell Heath,Essex'Phone: Seven Kings rzoo. 'Grams: Fuller, Chadwell Heath.

STAND No. 901 AT RADIOLYMPIA

POLARCONDENSERSSPECIFIED FOR THE

`GLADIATOR THREE'

The POLAR2 -GANG

BAR -TYPECONDENSERSteel frame ensuring greatrigidity. Aluminium vanes.Low minimum capacity.

PRICE 12/Ialso made in 2 -gang Superhcttype-I2/- and 3 -gang Super -het type-17/6.The above are available

I I

with Ceramic insulations for2 -gang -21- and 3 -gang 2,6extra.

POLAR DIFFERENTIAL

Improved design supplied withknob. Insulated spindle.

ONE .00015 REQUIRED

PRICE 3/ -

Also made in .0001 and .0003-Price 3/-.

11

SEE THE FULL RANGE OF POLARAND POLAR-N.S.F. CONDENSERS

AT STAND 97 RADIOLYMPIAor send for new illustrated Catalogue of Polar at dPolar-N.S.F. components.

WINGROVE & ROGERS LTD.188/189 STRAND, LONDON, W.C.2'Phone Temple Bar 2244. Works: Old Swan, Lh'crpool.

9511


Ask at stand 63Olympia for thesefour booklets

or post free lad. eachfor R104, R102, & R115(or 3d. for the three).No. R105 is 6d. postfree, or all four willbe sent for 8d. post

free.

write direct to

FERRANTI LTD.Radio WorksMoston Manchester 10.

FERRANTIC0111PONENTS

August 29th, 1936

Reliable Componentsare SPECIFIED for

GLADIATOR THREEB.T.S. Plug-in COILS

Two B.T.S. plug-in coils woundespecially for this receiver andas used by hlr. F. J. Camm inthe original.ACCEPT NO SUBSTITUTES.4 -pin, Type PEW4 3/33 -Pin, Tore PRWB 4/ -Exactly se specified.

STANDARD COILS as follows:4 -PIN Type E.1, 9-14, E.2, 12-20, E3,22-47. E.4, 41-94 metres, 2/9 each. E.5,

70.170 metres, 31- each. Eti, 150-3'25 metres, 3/3.1.7, 260-510 metres, 3/6. E. 6, 990-1,000 metres3;9. E.9, 1,000-2,000 metres, 4/-. 6 -PIN. Wave-anges as above. Type 4.1, 2, 3/3 each. 6.3, 4,

3 each, 4.5, 3/9. 4.6, 7, 4/-. S.A. 4/0. 4.9, 5/-.

B.T.S. 2 -BANK SWITCHLatest pattern anti -capacity multi -poleswitch. Heavilysilver plated con-tacts provide posi-

live connection.Rotary action and

Type C225.

roller lock-ing device.

B.T.S. COIL HOLDERS4 -PIN (illustrated). Sockets mountedon special low loss ceramic /6compound. Type 4CH I/6 -PIN. Similar to 4 -pin type butwith special low power factor 2/...moulding base. Type SPB

H.T.B. 3 -point Switch, Type PP3 1/3

BANDSPREAD S.W.3Slow Motion REACTION

CONDENSER.

Itigid, compact and highlyefficient. Brass vanes andend plates.' Perfectlysmooth action and thefinest degree of accuracywith a vernier motion of

10:1. Cap. .0002 mid.Complete withknob andpointer.rYPe RC39. 11)

H.T.S. u0.uuo d.'', Potentiometer. 3.9

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NAME

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PRAC. 29/8/36

X9511

THE

MOST SUCCESSFUL

ELECTRICAL WORK

OF THE YEAR

599

If YOU work inAny Branch of theElectrical Industry

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THE CATALOGUE WITH THE PURPLE &GOLD COVER


NEXT WEEK : STAND -TO -STAND REPORT

auct

India's Five -Year Plan

ACCORDINGto a recent announcement

-India has decided on a Five -YearPlan involving a number of low -powerstations which are to be erected in a numberof towns in the country. Short-wave trans-mitters are to be installed at Delhi, and onein Madras, and thepresent scheme alsoprovides for nine RouNDmedium -wave stationsto be located in variousparts of India. TheController of broadcasting, who was recentlyon tour through the rural parts of thecountry, has informed the Government thenature of the material for broadcasting inrural areas and the suitable hours of trans-mission. The director is of opinion that thevillager likes his own music, his own dialectand plenty of dialogues. Rural service,therefore, will be arranged on .a " five-minute " basis with music and occasionaldialogues and talks. Village musicians andstory -tellers will be engaged for the purpose.

Micro -wave Transmitter at BolzanoTHE recently opened Italian station at

Bolzano, which works on 20 kW, isconnected not only by cable but also has amicro -wave transmitter to ensure a goodrelay in the event of interference or othertechnical troubles which may cause a break-down in the link with its studios in the city.

fill' CCM

Technical Staff:W. J. Delaney, H. J. Barton Chapple, Wh.Sch.,

B.Sc., A.M.I.E.E., Frank Preston.VOL. VIII. No. 206. August 29th, 1936.

New Mexican StationsACCORDING to a recent report the end

of the present year will witness thebeginning of the wireless expansion schemein Mexico. Besides the construction oftwelve new transmitters for the transmissionof programmes to the neighbouring states,

the WORLD of WIRELESSit is proposed to add three short-wavestations to the strong Mexican network.Another Stratosphere Height Record

AREPORT issued by the U.S.S.R.Aerological Institute at Slutsk, near

Leningrad, states that a specially con-structed gas balloon fully equipped withradio apparatus was recently released inFrancis Joseph Land and attained the recordheight of 36,000 metres (118,800 feet).Tests on 75 centimetresIT is reported that at a recent radio

exhibition at Geneva demonstrationswere given of transmitters working on 75centimetres, and using a little over half awatt input. Signals were clearly receivedat rt distance of ten miles. Power wasobtained from a car battery, the voltagebeing stepped up by means of a vibrator andtransformer in the usual manner.

Bologna as a Key StationTHE 50 -kilowatt Bologna. (Italy) trans-' mitter has now adopted definitelythe wavelength 245.5 m. (1,222 kc/s), whichis the channel hitherto used by Trieste.It will act as the key -station of the NorthItalian network, and broadcast the Milan,

Trieste, Turin, andFlorence programmes.Occasionally it willalso transmit theRome radio entertain-ments.

25 W.B. Speakers as Prizes.Elsewhere in this issue appear details of an

interesting competition, free for all to enter,in which 25W.B. Speakers are awarded asprizes. The competition is of such a naturethat every reader stands an equal chance ofwinning one of the splendid 1937 StentorianSpeakers. Read the details now, and make upyour mind that one of those speakers is goingto be yours. The Editor of this journal willact as judge in conjunction with the W.B.Engineers, and the result of the competitionwill be published shortly after the closingdate.

Sunday Evening Concert fromTorquay

IN the National programme on. August30th the Torquay Municipal Orchestra,

conducted by Ernest W. Goss, will give aconcert from The Pavilion, Torquay, whenHarold Williams (baritone) will be the

Editorial and Advertisement Offices:" Practical and Amateur Wireless," George Newnes, Ltd.,

8-11, Southampton Street, Strand, W.C.2.'Phone : Temple Bar 4363.

Telegrams : Newnes, Rand, London.Registered at the G.P.O. as a newspaper and for transmission

by Canadian Magazine Post.


THE PICK of the PROGRAMMES" From the Esplanade "

THE fourth programme in the seriesentitled, " From the Esplanade," will

be broadcast from the Western Regionalon August 31st, when the Band of HisMajesty's Royal Air Force College (Cran-w ell, Lines.) (by kind per-mission of ' Air Vice -MarshallH. M. Cave -Browne -Cave, C.B.,D.S.O., and Officers), conductedby A. E. Sims, will play from theBandstand, Paignton. TheBand, which was formed in 1920,is one of the two official Bands ofthe Royal Air Force, and A. E.Sims has been the conductorsince 1932.

Marches and WaltzesTHE exhilaration of the

Military March and thelilt of the waltz have as wideand as irresistible an appeal asany other kind of music. Thepfogrannnes of marches andwaltzes which have been broad-cast in the past have invariablyevoked public appreciation, andthere will be many listeners whowill welcome another of theseprogrammes which is to bebroadcast on September 5th bythe B.B.C. Northern Ireland.Orchestra, conduct& by PhilipWhiteway. The programme isto include such popular marches.as " The Spirit of Pageantry,"" Marche Pompeuse," and theHighland Patrol, " The WeeMacGregor " ; the waltzes inthe programme include JohannStrauss's " Stories of the ViennaForest " and Eric Coates' " Atthe Dance " from the suite" Summer Days."

Concert from TorquayTHE Torquay Municipal

Orchestra, conducted by AErnest W. Goss, will be heardin a concert from The Pavilion,Torquay, on September 1st, when the soloartists will be Frederick Harvey (baritone)and Audrey Piggott (violoncello).

" Collecting the Mail "THIS is the title of the third actuality

programme in the series " In Passing,which will be broadcast from Bangor onAugust 31st. Twice a day, the Irish Mail,running from Holyhead to London, picksup the mail bags at various points en route.Outside certain stations, special gadgetshave been constructed so that the mail canbe picked up as the train rushes along.There are also receptacles for receiving themail bags which are dropped from the train.Most people in North Wales know that thishappens day after day, but very few knowhow it is done. The train passes throughBangor at about 12.40 in the day time andabout the same time in the' early morning.These times make it impossible to broadcastthe incidents as they take place, so that aepecial recording will be taken for the benefitof listeners, a day or so earlier. Post Officeofficials will be interviewed during theactual recording of the incidents.

The Bounty MutineersOWEN RUTTER (who recently pub-

lished a book on the subject) andCyril Nash have collaborated to produce a

television

1,41M1.4 11.8MI11.11111.1/1.1


radio play about the Mutiny on the Bounty.A recent film treated this theme somewhat

TELEVISING THE OLYMPIC GAMES

camera transmitting one of the eventsGames in Berlin.

imaginatively, but the play is based onmaterial collected from authentic sourcessuch as Admiralty records, Bligh's log andthe contemporary journal of JamesMorrison. In 1787 there was a mutiny onboard H.M.S. Bounty soon after she had

left England. The captain,Bligh, and eighteen of the crewwere set adrift, and after under-going almost incredible perilsand hardships eventually landedin England. The mutineers, ledby John Adams, settled on Pit-cairn Island in the Pacific andmingled with the natives toform a civilised community.Their descendants later settledin Norfolk Island. This roman-tic story, which should make ahighly dramatic radio play, willbe heard by Regional listenerson September 2nd.

during the Olympic

111.1.1101Mb :raz=s

SEI LIT 111 IS El.PROBLEM No. 206.

The voltage output from the mains unitof Brandon's receiver was 300 volts insteadof 250 volts. The normal H.T. currentconsumption of the receiver valves and theirassociated potentiometers was 50 m.a. Whatvalue in ohms should the required droppingresistance have, and what should be itswattage rating ? Three books will beawarded for the first three correct solutionsopened. Address your letters to the Editor,PRACTICAL AND AMATEUR WIRELESS, Geo.Newnes, Ltd., 8.11, Southampton St., Strand,London, W.C.2. Envelopes must be markedProblem No. 206 in the left-hand corner, andmust be posted to reach this office not laterthan the first post Monday, August 31st, 1936.

Solution to Problem No. 205.The centre tap could have been provided by means

of a centre -tapped resistance of 30 to 50 ohms connectedacross the two ends of the LT. winding.

The following three readers successfully solvedProblem No. 204, and books are accordingly beingforwarded to them : W. Wessell, Edge View, TheCompa, %Inver, Nr. StourbrIdge ; A. G. Arthurs,1, Emlyn Gardens, May Hill, Swansea; J. Robertson,Auckergill, Wick, Caithness.

Westbury

Students' SongsSEVERAL broadcasts have

shown that Harold Casey(baritone) and the B.B.C. Mid-land Singers, with Victor Hely-Hutchinson at the piano, makea strong team. They have beenheard in Songs of the Sea,Marching Songs, Soldiers' Songsand Students' Songs, and willbe heard again on Septeinter3rd.

Musical Comedy from Mid-land Regional

ON August 31st ReginaldBurston will conduct the

Revue Orchestra-the B.B.C.Midland Orchestra being, onholiday this week-in a pro-gramme of numbers drawn frommusical comedies. The RevueOrchestra consists of sixteenplayers, and the leader is NorrisStanley. The vocalist for thisprogramme will be Marjorie(soprano).

" Snappy' and " Happy "APROGRAMME which should prove

unusually entertaining has beendevised and written by Michael Carr, of" Red Sails in the Sunset " fame, andHarry Saville. Its full title is " Snappy'and ` Happy' take a Stroll through TinPan Alley." There is no real story runningthrough it. " Snappy " and " Happy " arotwo song writers trying to get a songpublished. They meet various otherwriters, and wisecracks are exchanged,leading to the introduction of the latestnumbers by these writers. Some of thenumbers will be played by Harry Savilleand his Band, while others will be playedby the composers themselves. Other songwriters who will take part include JimmyKennedy, Tolchard Evans, Harry Leon,Box and Cox, Ralph Butler, 'TommyConnor, Hamilton Kennedy, StanleyDamerell, Leo Towers, Paddy Roberts,Eddie Lisbona and Rodd Arden. Theproduction will be by A. W. Hanson.It is interesting to note that Harry Saville,who has assisted in writing and devisingthis programme, is not related in any way tothe Harry Saville whose band will pro-vide the music. This broadcast will be givenin the National programme on August 28th.

kugust 29th, 1936 PRACTICAL AND AMATEUR WIRELESS

To Our Readers-the Trade

Gentlemen,IT is fortunate that the opening of the Wireless Exhibi

tion coincides with the publishing day of PRACTICALAND AMATEUR WIRELESS because it enables us to publish,hours before the Exhibition actually opens, a completeguide to the Show and an illustrated forecast of theexhibits on each stand. The technical Press will notindulge in the panegyrics of the dailyPress, which can always be relied upon tomake startling news out of the mostmeagre material. On this occasion,however, we can excuse them if theyindulge in their usual flights of fancy andmake their usual mistakes in dealing witha scientific exhibition. Whatever theyhave to say about our Show will be an ap-preciated relief from their usual caterwaulabout politics and the European situation,for which each of them has its ownpanacea.

We know that the Press will be unani-mous in their praise of this Exhibition ;they will all tell you that the attendancefigures are up, that orders have beaten allprevious records, and that the receiversare better than ever before. I am, however, addressingthose who know how much reliance can be placed uponthese effusions, and it would he idle for me to adopt thosemethods. You will not mind, therefore, if during thisExhibition period when hopes run high I bring you backto earth, and discuss the Exhibition, and the prospects forthe ensuing year in the cold light of things present,basing my remarks about the prospects of the future onthe experience of the past.

I tell you that the public will be bitterly disappointedwith the very poor show of television receivers at theExhibition, and that home constructors will not fail tonotice that there will be very little, if indeed anything, onshow which specifically caters for them, from thetelevision point of view.

It is as well that I should tell my readers that tradeinterests have consistently opposed the commencement ofthe television programme, and that the programmescould have commenced more than a year ago had thetrade wished them to do so. I may tell my readers, and youcannot deny it, that you do not wish the home constructorto build television receivers, and it is indeed unfortunatefor you that in spite of your blockade they will he enabledto do so because of the many new firms who will springup to cater for their needs, and because of the co-operationof such firms in the component industry who are not tiedby the fact that they cater for both markets. For twoyears you have succeeded in stifling television, and thisyear you have accorded but a tardy welcome to the newscience and the new industry which it will support. I amaware that the patent situation is by no means a simpleone, but the Television Committee anticipated this bymaking provision for compulsory arbitration in caseswhere inventors and owners of patents sought to extractunconscionable rewards in the form of royalties. Everyoneis aware of the colossal sums still extracted from thepublic to pay royalties ; whilst we are in the hands ofpatentees you are helpless.

Your attitude has been directly responsible for the fact

603

that five firms will reap the business from the sale oftelevision receivers whilst you as passive resisters have beentoo busy passively resisting to investigate the possibilityof entering the television market yourself.

I am glad to be able to report that this journal continuesto be the leader in its field, that it has the largest netsales in that field, and that its considerable circulationconsistently maintained over the past year should indicateto you that the constructor market is by no means dead.Such a market is worthy of more attention than you havegiven to it. You built your businesses in the early daysfrom the home constructor market. They were theexperimenters who were responsible for the perfectionof radio ; they were the recruiting ground from whichyou drew your experimental departments, your salesmen,and your designers. It is true that having founded yourbusiness in this way you have endeavoured to destroy thatwhich created you by introducing the competition of thecheap, and in some cases nasty, commercial receiver.You really should have known better, because theconstructor is a discerning individual who knows thatyou cannot buy a really satisfactory wireless receiver fora few pounds.

The evidence of our circulation should satisfy youon that point, for very few genuine constructors havedeserted our ranks. It is not too late for you to makeamends ; the market is there, and it can be developed.When there is little to sell, there will be few to buy,although thousands are waiting to do so.

This journal has done its share in maintaining interestin the hobby, and since its inception, when it leapt to theforefront of wireless journals, where it has remained, wehave striven to hold readers' interest by making no chargeof any sort for answering readers' letters, by producingat considerable expense satisfactory designs and byproducing at nominal cost wireless handbooks forreference purposes. Yours has been the job to supplythe parts for those designs. In a few cases thoroughly


604 ' PRACTICAL AND AMATEUR WIRELESS August 29th, 1936

AN EXPERIMENTER'STEST BENCH

Details for a Useful Distribution Board and Test Panel by Means of ,

Which All Battery Voltages and Currents can be Read by Means of a ,

Single Meter While the Set is in Operation By The ExperimentersEXPERIMENTAL work is far - more

fascinating, besides being of muchgreater utility, if results can be checked

quickly and conclusively by means of testmeters. It is, therefore, an excellent planto have a bench equipped with a suitableterminal board and meters, which actsas a main distribution panel between thebatteries and the receiver ; where mainsequipment is used it might be possibleto arrange the panel between a standard t now available for about two pounds, and

Fig. 1.-This diagram shows thepoint at which voltage and currentreadings have normally to he taken.

supply unit and the set, but there aremore difficulties in this respect.

The bench itself can be quite a simpleaffair, consisting of an old table about3ft.. high, the top of which is coveredwith green baize or even light-colouredoilcloth. As to the distribution panel,this may be as simple or complex as desired,but details will be given of an arrangementwhich is fairly inexpensive, althoughcombining all of the most importantfeatures. First requirements are thatrapid and accurate measurements can atany time be taken of the H.T. voltageapplied to a particular set tapping, of thecurrent taken at any point, of the L.T.voltage and current, and of the G.B.voltage. Fig. 1 shows the points atwhich measurements frequently need tobe taken, the points at which currentreadings are required being indicated bycrosses, and those between which voltagemeasurements are needed being markedby arrows and a letter V. This is thesimplest arrangement of battery leads,and yet no less than eight meters would berequired if simultaneous readings were tobe taken at every important point. Itwould obviously be an expensive matterto buy eight reliable and accurate meters,besides which they would occupy a con-siderable amount of space.

Use of Plug and JacksAn alternative and better scheme, if

it could be adopted, would be to use asingle multi -range meter and to makeprovision for quickly applying it to anyone of the eight points. Actually, thereis little difficulty in this if the meter isfitted with a plug, and if jacks of suitabletype are included in the wiring. Themeter might be one of the many good types

MULTI-RAN4EMETER.

Fig. 2.-This illustration shows the connections tothe jacks at the same points as indicated in Fig. 1.

four single -circuit and four closed-circuitjacks are required. Single -circuit jacksare used for the voltage readings, the othersbeing for taking current measurements.The reason for using the latter is that thecircuit must be broken when the meter isconnected and remade when the meterplug is removed.

Jack ConnectionsThe idea will more easily be understood

TOLEALD.SS

TuAPPLETF

Fig. 3.-This shows howthe refinement of a choke -capacity output filter canbe added to the distribution

panel.

readings, and that when the plug is notinserted points marked 1 and 2 are short-circuited due to the spring contacts.The other jacks have only two terminals,these being joined one to each point betweenwhich the voltage is to be measured ; thus,the jacks have no effect when the meter -is not connected.

Suppose now that it is wished to measurethe voltage being applied to the terminalmarked H.T.+1, all that is necessary,is to set the meter to read up to, say, 150volts and to insert the plug into the jackmarked B. Similarly, the voltage toH.T.+2 is found by inserting the pluginto jack E. The current passing toH.T.+1 lead is found by adjusting themeter to read in milliamps and placingthe plug into jack A. In the same mannerthe G.B. voltage can be found by usingjack F, the L.T. voltage by using jack H,the L.T. current by using jack G, and30 on.

In connection with the wiring of thejacks, it should be noticed that the leadsto jacks D and G are the opposite wayround to those connecting jacks A and C.This is because these are in the negativeleads, and it is important that the correctpolarity of the meter be employed. Withthe wiring shown, the tip of the plug shouldbe connected to the positive terminal ofthe meter, and the main arm to the negativelead.

Panel LayoutThe method of arranging the jacks is

not important, but a panel such as thatshown in Fig. 4 is very convenient. Thisis made from a strip of ebonite, and is


1C Is"

0003 midVAR'. CON D

475PARE:'\LTO °Gel® HI C)

+ + : +2O

K1

Fig. 4.-A suggested layout for the distributionpanel described. The jacks are lettered in the

same order as in Figs. 1 and 2.

by referring to Fig. 2, where the jacksare shown in pictorial form. It can beseen that there are three connections tothe closed-circuit jacks used for current

Augiist 29th, 1936 PRACTICAL AND AMATEUR WIRELESS 605

ALL -WAVE ear..... ,

,; %4I f VP t .40 , 001/51 srse

IT was evident at the time of last year'sShow that interest in short-wave-andmore particularly all -wave --reception

was rapidly increasing. Since that timeall -wave reception has come intostill greater prominence andpopularity. The reason is notdifficult to find, for there areby now literally hundreds ofinteresting programmes regu-larly broadcast on wavelengthsbetween, say, 12 and 60 metres.Not only is the choice of prog-rammes wide, but reception overworld-wide distances on shortwaves is generally possible on even aninexpensive type of receiver. It isprobably because of the improved entertain-ment value of short-wave transmissionsthat increased attention is being paid tothis aspect of reception, but there are otherreasons, chief among which is that trans-missions of all nations are available, whilstthe listener can keep in touch with aero-planes, Atlantic liners, and even small craftexploring in the Arctic.

Long, Medium,- Short, and Ultra -ShortAnother reason for the greater interest in

short-wave listening is no doubt due to theshortly -forthcoming television trans-missions, which will take place on wave-lengths below 10 metres. As yet there arebut few commercial receivers which canbe used on long and medium waves as wellas on short waves down to 6 metres, butthere are some. The constructor, however,need have little difficulty in making. anall -wave set with an unlimited wavelengthrange. In this respect the constructor is inthe happy position of having " new fieldsto conquer," and short waves are un-doubtedly giving a fillip to home con-struction, as well as to the use of receiversof every kind.

A year ago the public paid close attentionto a commercial all -wave set (althoughthis was by no means new to the con-structor) ; special note was made ofreceivers which covered more than thetwo " standard " wave bands. This yearthe position has changed to such an extentthat there are as many all -wave models asthere are of those designed for medium -

1 '007f0/ivit

TIC>

/14.Z.W

if IN In MI IM

1M MI=

7700SMFD.

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and long -wave reception only. By nextyear two -band receivers will probably berare. Much of the pioneer work in develop-ing the use of short waves has been done

So Great Has Been the Interest. Shown in All -wave IReception in the Past Twelve Months that 1935-36 :x

Can Truly be Called The All -wave Year. Theix Principal Systems of All -wave Tuning/ are Described

'L.,x,..*._,,A,.. "By FRANK PRESTON-w-A- -.A,Aby the experimenter and constructor, andeven yet it is a field in which the con-structor does much more than hold his own.

Special ComponentsSome of the early all -wave models were

by no means reliable ; they were frequentlydifficult to operate, and were often onlymoderately efficient on any one band. Thisis certainly not true now, for the experi-menter, in conjunction with the more-

ALL-WRVETUNER

/

.0005- -0000.5 MFD.MFD. TRWIMER

TUNER

Hart

H.T*

Fig. 1-Skeleton circuit of a superhet pentagridfrequency changer using a pair of all -wave tuners.

progressive manufacturers, has producedreceivers which cannot justly be consideredas being a compromise. Manufacturershave produced several excellent examplesof all -wave tuners, tuning condensers, andother components of special short-wavetype which can be used efficiently on anywave -band, and the constructor has amplechoice. Let us hope that he will take fulladvantage of this, and continue to set thepace. PRACTICAL AND AMATEUR WIRELESShas endeavoured to foster this spirit, and

T/IFD.

Fig. 2-Skeleton circuit of a simple all -wave set of the H.F.-Det-L.F.type. The aerial circuit is aperiodic on short waves.

).H.7714

H.r

000/MFD.

ML S.

tiC

COIL

0005MFD.

was one of the first publications to offer toits reallers thoroughly sound, guaranteedand tested all -wave receivers; the latestof these designs is described in this issue

raid it marks a real forwardstep.

It is interesting to observethe various methods which havebeen adopted in producingdesigns for all -wave rpceivers,for they differ appreciably inmany instances. One of thesimplest, which can be adoptedwhen using a " straight "H.F.-Det.-Pen. type of circuit

is simply to arrange a switch to bringinto use a short-wave tuning circuitin the inter -valve circuit, leaving theaerial circuit aperiodic, as shown inFig. 2. This has the advantage of com-plete simplicity and the absence ofmulti -way switches, but it cannot be fullyeffective due to the fact that the first valveis little more than a " passenger " on shortwaves. Nevertheless, the system is valuablein that it obviates the need for specialtrimming and adjustment, besides whichit is inexpensive.

Another method which is better, althoughslightly more complicated, is that shownin the skeleton circuit, Fig. 3. In this caseboth broadcast (medium- and long -wave)coils are included in both the aerial andinter -valve circuits. In addition to thewave -change switches built into the broad-cast coils, two other change -over switchesare used to bring the short-wave coils intocircuit. The same gang condenser is usedfor tuning, and must, therefore, be providedwith a really good slow-motion drive.The change -over switches should be placednear to the coils, and they can best be ofthe chassis -mounting Q.M.B. type with acommon operating spindle.

An Interesting System- An arrangement which is often betteris that shown diagrammatically in Fig. 4.In this case a special three -gang condenseris used ; one section has a capacity of.0005 mfd., and the other two have a capacityof .00025 mfd. each. A third change -overswitch is required to place the two lattersections in parallel or to connect one to

(Continued overkaf)

Is. Ho-

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Fig. 3-This is a modification of the circuit shown in Fig. 2, and here bothcircuits are tuned on all wavelengths.

606 PRACTICAL AND AMATEUR WIRELESS August 29th, 1936(Continued from previous page)

each of the two short-wave coils. Thus,for long- and medium -wave reception thecondenSer acts as a two -gang .0005 mfd.condenser in the normal manner, whilst the two smaller sections are used as a two -gang .00025 mfd. condenser on short waves.Somewhat better tuning is often possibleby using this system, but much deirendsupon the design of the set as a whole. Thatthe extra complication is by no meansessential if the set is accurately designed isproved by the fact that it was found un-necessary in the " Gladiator " all -waverdescribed on other pages. Nevertheless, theidea is interesting, and many readers maycare to try it.

A simple modification of one of thesystems described can be applied to aDet.,L.F. type of receiver, and an example,is given in Fig. 5. In this case the reactioncircuit has been added, and the same con-nections could, of course, be used in thecircuits previously described it has beepomitted only for simplicity,aIt will be seen that a pair of ganged change-over switches is used, but in this case itwould generally be satisfactory and con-venient to use one double -pole chang&overswitch without the need for unduly longconnecting leads. A single .0005 mfd.variable condenser is used for tuning onall wave -bands, whilst one .0003 mfd.condenser is used for reaction. Both con-densers are connected to the appropriatecoil simply by rotating the double wave -change switch.

Various alternative reaction -switchingarrangements are possible, and it is, in fact,possible to obtain proper reaction controlon both wavebands by eliminating thereaction switch entirely and using the novelsystem employed for the " Gladiator."

Complete. TunersThose constructors who prefer to build

a receiver in the simplest possible mannerwill wish to use a complete all -wave tunerfitted with built-in switches. This com-ponent has been brought to a high degree of

0005 MFO /00025- - -GANGED -

Fig. 4.-An unusual all -wave tuning circuit inthree -gang condenser is used.

efficiency, and can be used in almost anycircuit as a replaceMent fOr in ordinarytuner intended for broadcast reception only.It was used in th; popular All -WaveThree " previously described_ in this jour-nal: and the circuit looks exactly the sameas that of an ordinary medium- and long -

Fig. 5.-Additional switching for the reactioncircuit. This system can be used on either set-

L.F. or H.F. receivers.

wave receiver. A'the switches are made;

(10'4." integral with the unit,and require no externalconnections, they can be'ignored by the con-structor, for they doall that the multiple,switches shown in theaccompanying circuit scan do.

Superhet SystemsWhen all -wave tuning

mr was first used experi-mentally it was found'that many difficulties

which a special occurred when buildinga superhet, but thesehave been completely

removed. This is partly because of theintroduction of pentagrid and triode-hexode valves, and partly due to thedevelopment of 465-kc/s intermediate -frequency transformers. The simplestMethod of all -wave tuning with a superhetis to leave the aerial circuit untuned onshort waves, either by leaving the normalbroadcast coil in circuit or by switching ashort-wave H.F. choke or a .25-megohmresistance in its place-and by tuning theoscillator circuit only. This can easily bearranged by tuning an all -wave coil fortuning the oscillator circuit, or by usingconnections based on those shown in Figs.1, 2 and 3.

An alternative, and rather better method'is to use broadcast and short-wave coils in'both input and oscillator circuits and to fita .00005-mfd. trimming condenser in paral-lel with the aerial -tuning condenser, asshown in Fig. 5. The extra condenser canbe set to its midway position on the medium'and long waves, and used for final tuningon short waves. Of course, there are manyother possible systeins, one of which is touse a special condenser designed on thesame principles as that shown in Fig. 4. Inthat case the larger section would be" graded " to suit the oscillator circuit

25 W.B. SPEAKERS FREEIN A SIMPLE FREE-FOR-ALL COMPETITION !

This year we again give every reader a splendid oppor-tunity of obtaining one of the new W.B. Stentorianspeakers entirely FREE OF CHARGE. The competition isextremely simple, and there is no entrance fee. Every entranthas an equal chance of winning one of the 25 speakersof the latest 1937 type, and illustrated on page 619 in thisissue.

The simple and straightforward rules are as follow:1. On the right is given a list of important features of present-day loudspeaker

You are asked to answer in the space provided, each of the six questions. Forsimplicity, you should insert the letter a" or b in reply to questions 1, 2, 3 and 5 ;write " yes or " no " in reply to questions 4 and 6.

2. Choose the three points included in the series of questions which you considershould receive greatest attention, and place them in order of importance in the spaceprovided. For example, if you think that quality of reproduction is most important,sensitivity next, and the inclusion of a " tweeter " next, you should write: 3, 4, 6.

3. After filling In the coupon, complete it with your name and address in blockletters in the space provided, and post in a soiled envelope addressed to:'TheEditor, PRACTICAL AND AMATEUR WIRELESS, Geo. Newnes, Ltd., 8-11, SouthamptonStreet, Strand, London, W.C.2.

4. Mark the word COMPETITION in the top left-hand corner of the envelope,and post to reach us not later than September 12th, 1936,

5. Readers may send in as many attempts as they like, in one envelope, providedthat each attempt is completed on a separate coupon, bearing the full name andaddress of the sender.

6. Only one speaker can be awarded to any one reader.7. The result will be published in our issue dated September 26th, 1936.8. The Editor's decision is final and legally binding-, and this Is an express

condition of entry. No correspondence of any kind can be entered into regarding thiscompetition.

WHAT ARE THE MOST IMPORTANT POINTSIN CONNECTION WITH A SPEAKER ?

1. What output do you require-under (a) orover (b) 3 watts ?

2. Do you prefer a mains -energised (a) or P.M. (b)speaker ?

3. Is " mellowness " (a) or natural reproduction (b)preferred ?

...

4. Should the speaker have a high degree ofsensitivity ?

5. Is a single (a) or double (b) unit preferred ?

6. Should there be a built-in " tweeter " ?

I consider the three most important items are :-

Name

Address .


iffeGladiator ALEWAVE 3A Super -efficient Receiver

Incorporating Some NewPrinciples of Design, Givinga Remarkably High Degreeof Selectivity and Sensitivity.

Wave Ranges are from 18to 55 Metres, 200 to 550-

THE 1936 Season closesand automaticallyopens the 1937. We

are on the threshold :of re-markable developments, whenvision will be superimposedon the sound programmes.Gradually, but none the lesscertainly, listeners are.evinc-ing greater interest in thatfascinating band below 100metres. where programmesmay be received from in-credible distances and pro-vide entertainment of a higherorder than that which resultsfrom the medium and long -wave bands. You may listento the gay chatter of amateursand the quaint programmesfrom foreign countries andfrom some of the Americanstations. If you have not yetlistened on the shortwaves, a new -experi-ence awaits you and anew thrill in receivingsome hundreds ofstations of which youhave never previouslyheard."But short-wave

technique differs Fromthat required for thenormal and long -wavebands, for short wavesare by no means soeasy to receive ; thereare certain times andcertain periods in theyear when reception isbetter than others. Ifyou wish, therefore, tolisten on the short-wave bands you maydo so by means of ashort-wave adaptor or;convertor, by means ofa special short-wavereceiver, or by meansof what is now knownas the all -wave re-ceiver. There are thosewho prefer a short-wave receiver only, butmany thousands wishto combine in one setthe features requiredfor ordinary listeningon the medium andlong -wave bands and

By F. J. CAMM

The Gladiator All -wave Three.

-Metres, and 850 to 2,050

Metres. The Receiver isExtremely Simple to Buildand Operate, and the Kitof Parts is Low in Cost.

Its Construction is Here

Described

those of an efficient short-wave set ready at a turn ofthe switch to transport themto the fascinating realm ofthe short waves. Few peopleare so situated that they canhave two receiving stationsin one house. Most havenot' the space for one thing,and owing to the widerange of components nowavailable there is now noneed to build two separatereceivers if you do not wishto do so.

There is an inconvenienceof disconnecting one receiverand connecting the otherwhen two separate sets areused for all -wave listening.Short-wave stations arebest heard late at night orin the early hours of the

morning. In the com-bined receiver there-fore you are able quick-ly to change from onewave band to another,at a time when youwould not be . inclinedto juggle about withtwo sets.

A Step Towards theUltra -Shorts

Let me therefore in-troduce you to theGladiator All - WaveThree, with which Iinaugurate the 1937season for home con-structors. With theadvent of the televisionprogramme, sooner orlater you will have tobecome acquaintedwith ultra -shortwaves, and if you havenot experience of theshort waves-a usefulstepping stone-youwill encounter diffi-culty.

The Gladiator hasbeen the subject ofcareful experiment inthe PRACTICAL ANDAmATEIIR WIRELESSLaboratories for thepast three months, andin the form in which


Cco._,"/WO

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it is here presented it is perfect, onall wavebands. It is not a compromisegiving you efficient service on one wave-band, by subtracting something from theefficiency of the other wavebands. Examinethe theoretical circuit. Here you willobserve that whilst it is a perfectly standardthree -valve straight circuit, it employsthree pentodes-one H.F. pentode forH.F. amplification, one H.F. pentode as adetector, and an. L.F. pentode in theoutput stage. The use of three pentodes inthis manner has distinct advantages whichI shall deal with later.

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August 29th, 1936

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Theoretical circuit of the Gladiator All -wave Three.

Two Tuned CircuitsContrary to usual practice of using an

untuned H.F. stage for short waves, twotuned circuits are used on all wavebandsof the Gladiator, thus extracting the verylast drachm of efficiency which it is possibleto obtain from such an arrangement ofcomponents. For, in very truth, theGladiator functions just as satisfactorily onthe short waves as it does on the otherwavebands. Tuning is delightfully simple,and the usual fierce reaction and delicatetuning associated with the short-wavereceiver is markedly absent. Another

Top and sub -chassis v'ews of the Gladiator.

G8.-1

important point which you will notice isthat iron-eore coils are used on the mediumand long waves, thus giving a high degreeof selectivity, plus a high degree of sensi-

Usually you can only obtain selectivityat the price of sensitivity and vice versa. Itried many arrangements of componentsto avoid this, and the circuit you see here-with achieves that very desirable result.

Notice that resistance -capacity couplingexists between detector and output valve,thus maintaining the efficiency owing to



491 ACAll -Wave Superhet 137 Gns. f

149All -Wave Battery 9 Gns.

Receiver (IncludingBatteries)

f 381 ACSuperhet with Spot

Light Tuning 12i Gns.

480 ACAll -Wave Superhet.

4 wave bands. 17i Gns.

4111 ACAll -Wave Superhet.

S wave bands 184 Gns.

No. 9.F Filing Cabinet. Hold,

400 Records (10'or 121 6 Gns

609

' 486 AC/DCUniversal All -Wave

Suoerhet 13d Gns.

482 ACAll Wave Superhet. Newtype Fluid Light) 16 Gns

ui ck I etetenceThe 38 years' experience which "His Master's Voice -Engineers have had in the design of sound -reproducinginstruments enables them to present a. range ofinstruments unexcelled for faithful reproduction.

From 8 gns.; or by hire purchase.

The Complete New Range of

"HISMASTER'S VOICE

. iil ave dad.

445 ACStation Selector Ray

Superhet 13 Gns.

545 ACStation Selector RaySuperhet Radiogram 22 Gns.

183

Wide AnglesoundDistributionSpeaker

£5 .17 .6

172

All PurposeMovingCoil,Speaker

I '3 Gns

485a ACAll -Wave Superhet Autoradio-gram. 5 wave Bands. 8 -record

changer. 36 Gns.

80 ACAll -Wave High Fidelity"Concert" Autoradiogram10 valves, S wave Bands8 -record Changer, New typeFluid Light. Clock. 3

Speakers, Record Cupboardsand 5 Albums 80 Gns.

s'4 6141-800All -Wave HighFidelity Autoradiogram. 15valves. 5 wave Bands 4 Range "HS MASTER'S VOICE -Selectivity device. 8 -recordChanger, Fluid Light, 2 98 108, CLERu-ENVrEil. ROAD, LONDON. E.C.-t'Speakers, Clock. 110 Gns.

- 5 8 1 ACAll -Wave: BureauSuper hetAuto -radiogram wave Bands,8 - record Changer, RecordCupboards. 6 Albums. 48 Gns.

622 ACSulaerhet Radiogramwith Spot Light

Tuning 22 Gns.

425 ACSupernet with A.V.C. 11 Gna.

8 Gns.(IncludingBatteries)

488 ACAll -Wave SuperhetRadiogram. 5 wave

Bands 26 Gns.

11

Pick - up and volumecontrol with screened

lead, 32/6


?Jour new cataloyue is readyIt isn't our policy to produce, by hook or by crook, something" amazing " for the Show. This is principally because our laboratoryis making improvements and advances so frequently that we'vejust ceased to be amazed.Besides, we feel confident that you know just where you can finddetails of the very latest developments both of condensers andresistances in this country. The new Dubilier catalogue is nowready and we shall be very pleased to send you your copy.Then you'll he right up to the minute.

BUBILIERCONDENSERS

r: ILIER CONDENSER CO. (1925), LTD., DUCON WORKS, VICTORIA ROAD, NORTH ACTON, LONDON, W.3.


View of the wave -change switch and reaction control of the Gladiator All -wave Three.

(Continued from page 608)the use of H.F. pentode detector, which ismore sensitive than a triode deteCtor

transformer coupled to the output valve.'A more important point, however, is thatR.C. coupling in this stage ensures freedomfrom that great drawback threshold howl.

An External TrimmerAnother feature which the reader will

appreciate is that a trimmer is attachedexternally to the gang condenser andprovided with a knob, so that minute finaladjustments can be made on all wave-bands without having to remove the chassisfrom the cabinet and to toy around withinsulated screw -drivers.

The wave ranges covered are 18 to 55metres, 200 to 550 metres, and 850 to2,050 metres, and it is particularly necessaryto adhere very carefully to the layout andIto the specification in order to achievesatisfactory results. Our standard systemof construction has been employed usinga metallised chassis. 'The constructionitself calls for very little comment, for itfollows the practice we have described somany times in this paper.

Blueprints AvailableThe receiver is built up on a Metaplex

chassis measuring 10in. square, and Irecommend readers to enlarge the scalewiring diagram given herewith so that thecomponents occupy the same relativepositions as in my receiver. If they preferit we can supply a full-size blueprint -forls., and orders should be addressed toblueprint Dept., Geo Newnes, Ltd., 8-J1,Southampton Street, Strand, W.C.2. It ismost important that you should not alterthe position of the components in any way,for the whole circuit has been carefullybalanced and the stability of the receiverdepends upon the components being placedexactly as in the original.

In drilling the holes for the valveholdersit is important to drill a clearing hole sothat the legs are not shorted by the Meta-plex covering. Messrs. Peto-Scott Co.,Ltd., supply the chassis ready drilled, andif you purchase from them you will berelieved of the responsibility of drilling theholes and of spacing the components.

The SwitchThe switch connections need to be care-

fully studied, and to make the matter, quiteclear a separate switch connection diagramappears on page 612. This, in conjunctionwith the theoretical circuit, should removeall difficulties.

VISIT OUR STAND

No. 10GROUND FLOOR

Carefully adjust the extension rods sothat the switches move freely, and makesure before wiring up that positive contactis being made in all positions. Keep theleads as short as possible, and ascertainthat no loose ends can make Contact withthe metallised. chassis. -Where it is neces-sary to pierce the chassis to receive a wire,make sure that the insulation is perfect.Quite often I have found that failure toobtain results has been due to fraying ofthe insulation which has been chafed barewhen being Pasied through a rough hole.

Packing the CondensersNotice that the variable condenser is

mounted on a, packing piece in order to'centralise the driving spindle with the con-denser drive, as the J.B. horizontal drivewith trimmer (not supplied by the makersof the variable condenser) does not pair upwith the variable condenser. Select a pieceof wood of such thickness that the drivepushes on without strain. It is true thatvertical adjustment of centre height isprovided on the drive, but it is insufficientto align with the condenser spindle. Thepacking piece of wood is supplied with thechassis when this is obtained from Messrs.Peto-Scott.

The Speaker Lead, Speaker Sockets,etc.The speaker lead which connects to V3

must be kept well away from V2, as shownin the sub -chassis wiring diagram. Theaerial and earth and loudspeaker socketstrips should be carefully fixed and holesfor the sockets should be of clearing sizeso that the metallised covering does notshort-circuit them. It is always safe toscrape away the metallised coating for anarea which completely clears the rectan-gular pieces of insulating material to w4ichthe sockets are attached.

The ControlsThe relative positions of the controls will

be apparent from the cabinet -drillingdiagram given on this page, and the com-

3ch"

3

Cabinet -drilling diagram of the Gladiator All -wave Three.


WIRING DIAGRAMS OF THE GLADIATORALL.WAVE THREE

11

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August 29th, 1936

ponent-mounting brackets should be fixedin the positions shown to give a sym-metrical layout. In order to drill thecabinet the knobs are removed, a spot ofink is applied to the centres of the spindles,and the chassis pushed in to the cabinet.The spots of ink will be transferred to theinside of the front of the cabinet and thus

Connections to the Switch Unit.clearly mark the hole centres. Drill a smallhole through from the back and then openout the holes to the correct size from thefront. In this way you will avoid splittingthe polished front of the cabinet.

LIST OF COMPONENTS FOR; THE GLADIATOR ALL -WAVE

THREEOne 2 -gang coil unit (BP50, BPSI) (Varley).Two short-wave coils (special) (B.T.S.).One 2 -gang condenser (C1, C2) (Polar)

; One two bank multi -switch (B.T.S.).One .00015 mfd. differential reaction con-

denser (C3) (Polar).One horizontal drive with trimmer (SL9)

:; Three valve -holders (two 4 -pin, one 5 -pin),

V3 (Clix).Two coil holders (one 4 -pin, one 6 -pin)

(B.T.S.).; Two extension rods (E.H.2) (Bulgin).

One volume control, 50,000 ohms, with3 -point switch (R7) (Erie).

Six fixed resistances :.5 meg. (R1), 1,000 (R2):100,000 (R4), 100,000 (R5) 2 meg. (R3),1 meg. (R6) (Dubilier).

i Seven condensers :.1 mfd. (C6), .1 mfd. (C8),.01 mfd. (C5), .01 mfd. (C9), .0005 mfd.(C4), .0001 mfd. (C7), .003 mfd. (CW)(T.C.C.).

Five component brackets (P. Scott).Two terminal strips : A.E. and L.S. (Clix).One 100 m.a. fuse and holder (Microfuse).Three valves: 210V.P.T., 210S.P.T.,

220H.P.T. (Cossor).One Metaplex chassis 10in. by 9in. by 3in.

(P. Scott).One speaker (37J) (W.B.).One cabinet (P. Scott).Seven plugs : H.T.1, H.T.2, H.T.3, H.T.--,

G.B.+, G.B.-1, G.B.-2 (B. Lee).Two spades: L.T.+, L.T.-. (B. Lee).

August 29th, 1936

SUMYOURIDEA.



Improvised Pillar InsulatorsUSEFUL pillar insulators, suitable for

supporting bare H.T. wires or aeriallead-in, can be constructed from the

SG. VALVETERMINAL

FILLED WITHMELTED PITCH.

Easily -made pillar insulator.

" caps " of " dud " screened -grid valves.Fill two caps with melted pitch, place

the two filled caps together whilst the pitchis hot and hold firmly until the pitch cools.One end of the pillar may now be securedto a wood or metal baseboard by thethreaded screw, and the insulated terminalat the other end used to secure the H.T. oraerial wire. These pillars are particularlyuseful for short-wave sets.-F. C. EDWARDS(Derby).

An Efficient Morse KeyTHOSE who are learning morse or who

are amateur transmitters need anefficient key. The accompanying sketchshows how I made one at a cost of about 6d.First cut a piece of ebonite .sheet to aconvenient size for the base (4k in. by 31 in.by fin.), and then cut four ebonite feetfor the base and screw them on to it, oneat each corner.

Now take a piece of brass rod 4in. by fin.by fin. and at fin. from one end drill ahole and put through it a round -headedbolt and hold it fast with a nut. On tothe end of the bolt fasten a knob.

At 2k in. from the knob end, drill a holeat 90° to the first one and through it puta piece of rod, about lf in. long. By meansof two telephone terminals fastened to

SPINDLE

BRASS ROCKERARM 4"XYX.4"

THAT DODGE OF YOURS!Every Reader of " PRACTICAL AND

AMATEUR WIRELESS" must haveoriginated some little dodge which wouldinterest other readers. Why not pass it onto us ? We pay £1-10-0 for the best wrinklesubmitted, and for every other item publishedon this page we will pay talf-a-guinea. Turnthat idea of yours to account by sendirig itin to us addressed to the Editor, " PRAC-TICAL AND AMATEUR WIRELESS,"George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, W.C.2. Put your name andaddress on every item. Please note that everynotion sent in must be original. Markenvelopes " Radio Wrinkles." Do NOTenclose Queries with your Wrinkle.

iS

the ebonite base, support the arm of thekey by passing the rod through the holesin the terminals and the arm. At theother end of the arm fasten one end of acoiled spring, and fasten the other endof the spring to the ebonite base, by meansof a nut and bolt. Between the spring andthe pivot put an adjusting screw to varythe size of the contact gap.

The contact gap consists of the bolton to which the knob is fastened, andanother bolt fastened- on the ebonite basedirectly beneath it. For good results asmall piece of silver should be soldered onto each of the contacts.

A simple resistance board.

A wire is taken from the bottom contactand another from the pivot. These wiresgo to two terminals situated at the end ofthe ebonite base remote from the knob.

I have used this key for morse practicefor some time and have found it veryefficient.-R. Q. MARRIS (Exeter).

ADJUSTINGSCREW

A cheap but efficientmorse key made fro n

odds and ends.

A Resistance BoardTHE accompanying

sketch shows a re-sistance board of a similardesign to the capacityboard described on thispage in PRACTICAL ANDAMATEUR WIRELESS forJuly 25th, 1936. It con-

` gists of four fixed resist-ances and five terminalsmounted on an ebonitebase. By taking a con-nection from terminal 1and another from a wirejoining terminals 2, 3,and 4, a resistance of54.5 ohms is obtained.

..Thirty-five different fixedresistances between 4

613

and 700 ohms can be obtained from thisdevice by making the connections shownby the following tableResistance. Connections. Resistance. Connections.

48 1-2, 3,54.5 1-2, 3,57.1 1-2, 3,63.1 1-2, 4,66.6 .1-2, 375 1-2, 480 1-2, 692.3 1-3, 4,100 1-2120 1-3, 4133.3 1-3, 5171.4 1-4, 5192.3 2-3, 4,200 1-3220 2-4, 3233.3 2-3. 5238 2, 3--4,263.1 3-2, 4,

-R. HOLDEN (Blackburn, Lanes.).

4, 5 271.4 2-4, 54 275 3-2, 45 280 .3-2, 55 300 1-4

357.1 4-2, 3, 5366.6 4-2, 3371.4 3-4, 5

5 380 4-2, 5400 1-5433.3 4-3, 1454.5 5-2, 3, 1

466.6 5-2, 35 475 5-2, 4

600 2-5520 5-3, 4

600 3-55 700 4-35

A Solder Reservoir for an ElectricIronANY electric soldering iron not having

a thin bit, can very simply be adaptedto include a solder reservoir. The bitshould be drilled and filed as shown in thesketch, the 1 in. hole being carefully drilledfirst, and the 1/32in. hole then being drilledthrough to it from a centre -punch mark

on the point of the bit.The position of this holeis very important, as theunder -surface of the bit

--should continue right tothe point, beneath it,although the bottom ofthe hole should be as lowas is possible.

The * in. hole shouldhold sufficient solder foruse on radio work, but aheavier iron for biggerwork could well have a*in. reservoir. The 1/32

4 in. feed hole may notalways be sufficient, but it is wiser to startwith this size, and enlarge if necessary.

The bit must be well tinned before use,and the tinning should never be allowedto become burnt away round or in thereservoir hole. The feed hole shouldoccasionally be cleaned with a piece offine wire, which can be kept in the holewhen the reservoir is being used forwire tinning.-D. L. JouNsroisr (Brighton).

Adapting a solderingbit to include a solder

reservoir.

614

icr

r ;11 1 111- V

August 29th, 1936. Vol. 3 No 16.

AT last the Alexandra Palace televisionstation has begun to radiate high -definition signals. A few days ago

both companies completed their chain ofequipment-scanners' modulation ampli-fiers, and ultra -short-wave radio trans-mitters-and as soon as the B.B.C. aerialinstallation was finished the aerial feederwas linked up and pictures broadcast.The Baird Company were the first on theair and a number of standard talking filmreels were televised, the results judgedfrom the point of view* of detail and syn-chronism being most praiseworthy for thefirst effort. The next day the Marconi-E.M.I. Company brought into commissiontheir Emitron camera (the iconoscopedeveloped., originally by Zworykin) andactual studio and exterior scenes weretelevised with most promising results. Atthe moment no form of service is contem-plated, the companies concerned devotingthe whole of their energies to ensuringthat the radiated pictures reach full effi-ciency. The fact that television picturesare available naay alter the whole situationas far as the Radio Exhibition is concerned,although at the time of writing it is not yetknown officially whether demonstrationswill be featured, the atmosphere of un-certainty which has prevailed right up tothe last minute has made it difficult formanufacturers of receiving equipment tocome to any decision, and there now seemslittle likelihood of any large-scale demon-strations being effected on lines comparableto those which characterise each year'sBerlin Show. The most pleasing feature,however, is that a start has been made,and it is certain that little time will now belost in bringing the first B.B.C. high -defi-nition television station into full commis-sion, so that those interested in receptioncan have full scope for their capabilities,whether use is made of home -constructedequipment or commercially made receivers.It is learned that the two television receivermodels will be shown on the H.M.V.stand, and a similar number on the BushRadio stand, which company is marketingthe Baird sets.

From the U.S.A.David Sarnoff, who is chief of the Radio

Corporation of America, is in this countrywith the express purpose of seeing the mostrecent developments in television. Asso-ciated with every form of modern enter-tainment and responsible for the elaboratetelevision equipments now being conductedfrom the Empire State buildingin New York, as detailed inprevious issues of this journal,he is anxious to see whetherBritain is very far ahead ofwhat is being undertaken in theU.S.A. After that, a visit toGermany is contemplated toinvestigate the work done inthat- country, where an experi-mental service has been radiatedfor such a long time.

In CinemasAmbitious plans for the in-

stallation of television in cine-

PRACTICAL

mas are now being made with the objectof bringing this newest scientific develop-ment to the notice of patrons bypicture reproductions on screens almostas large as those employed for the

IILATESTNEWS OF THE !

!TELEVISION RECEIVERS ARE.

GIVEN ON PAGES 630 and 631

standard talking film projection. OnePaddington cinema has already had theplans passed for this work, the system to beused being that of Scophony. This uses thewell-known mechanical methods, it beingstated that the two dimensional scan broughtabout by the stixograph associated with a

AND AMATEUR WIRELESS August 29th, 1936

brilliant light source, and signal modulator,is capable of giving pictures at the nacmentwhich fill a twelve -foot screen. This isdirect projection, and differs very materiallyfrom the intermediate film method which hasalready shown itself capable of giving satis-factory results. Yet another scheme isassociated with the latest form of projec-tion type cathode-ray tube, and with theseand other methods already. being tried itseems certain that television in the cinemawill be an accomplished fact very soon afterthe successful establishment of a televisionservice for the home.The Olympic Games

Very elaborate plans were made at theBerlin Stadium for televising the OlympicGames this year. Two mobile intermediatefilm scanners and three iconoscopeEr Werebrought into service, these being positionedat points of vantage in the ground. Bothvision and sound signals were radiated forthree periods daily ; namely, 10 a.m. tonoon ; 3 p.m. to 7 p.m. ; and 8 p.m. to10 p.m. ; the main events forming thesubject matter of the pictures. While this'is not the first time that outdoor sportingevents have been televised, it is the firsttime that such a big" scale 'test has beenmade. The standard of definition wasone of 180 lines, 25 frames (and pictures)per second, and a total of thirty viewingrooms were opened so that members of thepublic unable to visit the Stadium could seethe happenings under conditions neverbefore attempted. The total accommoda-tion approached 3,000 and, since admissionwas free, the viewing rooms were alwayscrowded. In addition to standard typecathode-ray tube receivers being installedat the receiving points, two of the theatreshad larger screens employing cathode-rayprojection equipment. As was to be ex-pected, the results were far from perfectand varied from period to period. Manyof the sporting events were recognisable,however, and the information obtained bythe engineers during the fortnight's workwill be invaluable for organising futureoutside television broadcasts.

Woman Make-up ExpertThe problems associated with questions

of colour when televising studio subjectsat the Alexandra Palace are so importantthat the "B.B.C. have appointed a womanmake-up expert (Miss Mary Allen) to adviseartists and announcers what to use andalso supervise the wardrobe. Very broadly,it is found that colours can be dividedinto three categories ; namely, blacks andblues, which appear black ; grey, darkbrown and dark green, which appeargrey ; and white, red, light brown and mostpale colours, which look white. Clotheswhich are relieved by contrasting colourswill be featured so as to secure the besteffects from the pictorial point of viewand do justice to whatever performanceis being featured from the televisionscanners. The problem is made some-

what more complicated bythe fact that the electroncameras need different colourtreatment from the intermediatefilm scanner, but once a completeschedule of colour effects hasbeen drawn up the resultsshould be quite satisfactory.

The new wireless mast at Alexandra Palace, the home of the firstofficial television station in London, which is to be opened in

the near future.

A Manchester TestIt is stated that in Manchester

a secret invention for showingtelevision pictures in theatresand cinemas has been demon-strated. This was undertaken in

(Continued on page 01.)

August 29th, 1936 PRACiiCAL AND AMATEUR WIRELESS 615

THE MAINSMODELS 375 and 375U

_Mtee Awh

CossonSUPERSETS

/or

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D.C./4.C. MAINS

OPERATION

SEE THE FULL RANGE OFCOSSOR RADIOSTAND No. 55

RADIOLYMPIABrief Specifications:BATTERY MODEL 376B (Class " B" Output)(5 VALVES)Compensated Anti -fading Circuit, with Pentagrid Frequency Changer,Var.-mu H.F. Pentode I.F. Amplifier, Double Diode znd Detector.Power Driver and Class " B " Output. Full Vision Dial with stationnames. Combined Volume Control for Radioand Gram. 8" M.C. Speaker. Provision forExtension Speaker and Pick-up. Full accom-modation within Cabinet for Batteries. G.NSIPre Pa-ebase Terms: 12 /7/03/bS 14/- deposit and 12 payments of x5/9.

IS months 14/- deposit and IS payments of 11/3.

A.C. MAINS MODEL 375(=, VALVES INCLUDING RECTIFIER)Compensated Anti -fading Circuit, with inidirect!y heated Pentagrid Fre-quency Changer, Var.-mu H.F. Pentode I.F. Amplifier, Double DiodeTriode 2nd Detector/Amplifier, Directly heated Power Pen. Output, -IeavvDuty Rectitier. Full Vision Illuminated Dial with station names. Single -knobTuning. Combined Volume Control for Radio and Gram. Toneadjustment. 8" M.C. Speaker. MagnificentWalnut Cabinet. Provision for Extension 1Speaker and Pick-up. A.C. Mains 2oo;25o 2- GNSvolts (adjust.) .10;1 oo cycles.

Hire Purebax: Terms: 12 months 17/6 deposit and 12 payments of 17/3.mintbs 07/6 deposit and 18 payments of 12/6.

D.C./A.C. MAINS MODEL 375U.(5 VALVES INCLUDING RECTIFIER)Universal model generally similar to above.For D.C. zoo,'25o volts (adjust.) and A.C.200/250 volts (adjust.) 5otzoo cycles. GNSHire Purchase Terms: 12 months 18;6 deposit aid it payments of 18/..

18 months 1816 deposit and 18 payments of 12/9.Prices do not apply in I.F.S.

A. C. Cossor Ltd., Highbury Grove, Highbury, N.5.

WHETHER you useBatteries or whether youhave A.C. or D.C. Mains,you can now have all theadvantages which up-to-date Superhet practicebrims. These models,with their Full Auto-matic Volume Control,their Variable -mu H.F.Pentode Stage, their Su-per -selective Coils and,very important, theirDistortionless Detector,ensure really life likereproduction at amplevolume. Hear and judgethem for yourself at anygood wireless shop.

BATTERY MODEL 376Bwith CLASS ' B ' OUTPUT


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AN EXAMPLE FROMTHE NEW RANGE OF

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August 29th, 1936

4.0-1(ta.

A 9&C QUALITY BATTERY FOR EVERY SET

of The General Electric Co., Ltd., Head Office & Public Showrooms : Magnet House, Kingsway, London, W.C.2.

August 29th, .1936 PRACTICAL AND AMATEUR WIRELESS

The Glorious Eleventh'HE publication of this issue

t i coincides with the opening ofthe eleventh Radiolympia. I do notknow whether the Radio Manufac-turers' Association have selected thatone -day -in -the -week when we havesufficiently recovered from Mondaymorning ennui to anticipate therelaxation of the week -end and be inthe mood to visit an Exhibition, orwhether they feel that it would bebest to open the Exhibition on theone red-letter day in the week forwireless enthusiasts-that on which theleading wireless weekly, PRACTICALAND AMATEUR WIRELESS makesits appearance. I am necessarilywriting these lines some days beforethe Exhibition opens, for time, tideand printers wait for no man,AssOciation, or exhibition, and I mustgaze into the cerulean blue, embarkinto the realms of vaticination and ina word indulge in ballyhoo.

In sinning thus I do so in goodcompany. I know exactly what willbe in next Wednesday morning'snewspapers. The daily paper " ex-perts will tell me that this is themost marvellous exhibition ever. Ishall be told that never before in thewhole history of radio has suchremarkable value, such outstandingquality of achievement, such stunningcabinet work, such omniscient in-genuity been staged for the benefitof the listener. In Thursday morn-ing's newspaper I shall read that mostof themanufacturers during the firsthour of the Exhibition sold theirentire output for the next three years.You will read last year's Show Reportdished up with a few more super-latives to provide the topical note.It is a strange thing that manufac-turers who have sold their entireoutput for the next three years con-tinue to exhibit, since most of themtold me this story three years ago and,

617

OA 016aVOINwith that perspi-cacity for which Iam Jenowned, Iobserve each year

towards the end of each wirelessseason that sets are being sold in thejunk shops at half manufacturer'sprices ! Perhaps, my reader, you canenlighten me on these things ; it maybe that I cannot see the wood for thetrees ; it may even be, with thatobtuseness which causes me to fail toperceive music in crooning, or melodyin dance music, that my cerebellumcannot appreciate the finesse of thesethings. I have a poker face, and canplay a good hand of Bridge. I canpot the red with unfailing regularity.If you can remove some of the furrowsfrom my brow by explaining why,each year, manufacturers make moreand more sets, sell more and more sets,dispose of their entire output in anhour and are still able to make thesame receivers at half price for thejunk shops, do please drop me a line ortwo on a postcard. A picture post-card for preference-I collect them.

BallyhooAND yet, in my unwisdom perhaps

I know that I like a certainamount of ballyhoo. It provides theright atmosphere, that mystic thingwhich originally emanated from thestage and the glamorous precincts ofthe theatre. I know, also, that thenight before the Show I shall visitRadiolympia, and wonder how onearth the Exhibition can open on thefollowing day. I shall have that sameschoolboyish feeling of anticipatorypleasure on Tuesday night, and, inspite of the fact that years of listeninghave jaundiced my outlook and maybewarped my reasoning, I shall enjoymy daily visit. I have no secrets topass along to you, for I honestlybelieve that this year the mixture willbe very much as before. There willbe the so-called improvements, won-derful tuning systems, which tell youwhen you are receiving a station youought to get but can't. There will

he fresh shapes to old objects ; theattractive damosel to ogle the doubtingpurchaser. There will be the samegood sets, and the same had sets inequally tempting exterior cabinetwork ; the same tired and harassedcrowd.

The Cabaret or the Show?IKNOW in advance that all records1 for attendance is going to he broken,and I shall make my usual estimatethat seven -tenths of the people whovisit Radiolympia in the evening enterits hallowed portals for the basepurpose of seeing the cabaret ! Theywill kill time by looking at exhibitsthey have no intention of purchasing,in the same way as you visit Whipsnadeto see the giraffes, or the antics of thesimians. Only the discerning will beable to separate the wheat from thechaff, the good from the bad. Onlythe knowledgeable enthusiast will failto be misled by a tastefully engravedtuning dial, containing hundreds ofstation names which beguile you intothinking that those are the stationswhich the set will receive. Theshock comes when you find the localspreading over half of them.

Build Rather Than Buy.OF course, no reader of this journal

comes within that category. Theybuild rather than buy, not because ofpecuniary considerations but for thejoy of building. This enthusiasticband has, in my opinion, always beenbadly catered for at Radiolympia.I have always felt that the componentsection of the Exhibition should besegregated. As it is, you find com-ponents mixed up with sets, in thecase of those firms who cater for bothmarkets. The number of firmsspecifically catering for the homeconstructor has, it will be observed,shrunk to meagre proportions. It isnice to know that many of the leadersremain. The fact that so many firmshave fallen by the wayside does notindicate a commensurate shrinkageof interest on the part of the consumer.

618

In all new industries there are thosefirms who jump in and jump out,who have no knowledge of therequirements of the public, and areprepared to sell the merest trash byblatant advertising and misstate-ments. When the public is unaccus-tomed to the wares of the newindustry it is easy to do this. As soonas the public develops a sense of valueand accumulates a nodding ac-quaintance with the science such firmsfail and rightly so.

Television This Year, Next Year ... ?IN this refining process the good

firms suffer hurt, and they have toawait their just reward. That timehas just arrived, particularly withthe dawn of the nebulous televisionservice.

The television industry arrives ata time when the public is radio -minded and not to be so easily caught.I do not anticipate that there will bethe same influx of mushroom firms,and we shall not arrive at a satisfac-tory stage after several years ofscandalous exploitation as we didwith radio ; but you never can tell !

Pride of possession is always likely toblind our acumen. As soon as Mrs.Brown tells Mrs. Smith next doorthat Mr. Brown has bought a tele-vision receiver the pangs of jearousyare aroused, and Mr. Smith will be infor a harassing time until his spouseis on an equal footing with Mrs.Brown. Mr. Brown will thereupondash out and buy anything whichlooks like a television receiver, onlyto regret after havina seen one builtby, say, a reader of this journal, thathe did not wait a little longer.

I cannot promise you that televisionreceivers will preponderate atRadiolympia. As far as I can see,only about four firm will exhibitsuch receivers, and it is not knownat the moment of writing whether apublic demonstration will be stagedat Radiolympia. In any case itwould seem that such a venue wouldnot be suitable because of the electricalinterference.

No one knows when the televisionservice will start, in spite of the factthat it is nearly two years since theTelevision Committee issued itsfamous report that " the momentwas ripe for a public television service."If the moment was ripe two yearsago it must be particularly putridnow, for it has long passed the over-ripe stage !

And speaking of television, someyear or so ago a certain well-knownradio publicist stated that televisionreceivers would require at least 3ovalves. I challenged him on this,because his remarks were widely


Superhet Selectivity

THE selectivity of superhets de-signed for an intermediate fre-

quency of I x o kc/s is usually greaterthan that of receivers employing ahigher frequency. It is possible, how-ever, to improve the degree of selec-tivity in high I.F. superhets by makingthe I.F. valve oscillate when the H.F.volume control is at its maximumsetting. This can be done in severalways, the easiest being to bring thegrid and cap leads of the. I.F. valve.near each other. This has the sameeffect as the application of reactionin a straight receiver. Sensitivity isalso improved when this is done, butquality of reproduction generallysuffers in the same way as it doeswhen reaction is applied to the straightset detector.

C.W. on Short Waves

THIS dodge can also be made useof in short-wave . superhets.

Most morse transmissions are madeon C.W. (continuous wave), andthese cannot be picked up on thenormal short-wave superhet. It isnecessary to use a reacting straightset or to provide reaction in the I.F.or second detector stage of a superhetbefore C.W. transmissions can bereceived. If the I.F. valve is madeto oscillate in the manner explainedabove, the number of stations pickedup will be more than trebled. Whentelephony programmes are to bereceived the valve must be in a non -oscillating condition, of course, andthe oscillation must therefore becontrollable. If the bias voltage typeof H.F. volume control is fitted, thiscan easily be done.

Operating D.C. Sets from A.C.

WHEN the consumption of theD.C. receiver is not more than

about 6o watts, the easiest method ofsupplying it from A.C. is by means ofa transformer-metal rectifier com-bination. Two rectifiers of the H.T.

x type should be used, connectedin bridge formation ; that is, positiveto positive, negative to negative, withthe secondary leads of the trans-former connected to the A.C. ter-minals of the rectifiers. The positiveinput lead of the D.C. set is thenconnected to the juncture of the tworectifier positive terminals and thenegative input lead to the rectifiernegative terminals.

August 29th, 1936

quoted. What does he say nowwhen it is known that the number isdown to 20, and in one case to 54. ?Of course, he made his remark with histongue in his cheek, fearful lest theindustry which he represented shotildlose sales of ordinary wireless appara-tus. I say that it is largely due to theattitude. of the wireless industry itselfthat television has not been availableat least a year ago.

Television has provided the price-less example of one industry tryingto circumvent another. Still, themain thing is that the industrythrives ; its output grows each year,and it is absorbing more and moreof the unemployed.

Radiolympia

ITis the one opportunity which 'the

listening public haS of visiting theentire industry under one roof..Itis the one opportunity provided .for meto meet my friends and enemies, andwe should view the exhibition in thesame light, as a holiday at the seaside,when we spend foolishly and actfoolishly and in a manner which weshould not do when at home. Getthe holiday spirit and loosen thepurse strings when you visit Olympia !And good hunting to you.

The Teacher PaysCOMMENTING on' a report,

Mr. A. E. Henshall; secretaryto the education committees of theNational Union of Teachers, told aPress representative in London :

" Broadcasting is a new andvaluable education development andis recognised as such by most teachers,and the more enlightened localeducation authorities.

" Yet there is little doubt that theconditions outlined in the Staffordshirereport give a fair indication of whatis happening throughout the country.

" Enterprising teachers seek the aidof ' broadcast ' talks for the bettertraining of their scholars, but fre-quently they have no option but tobuy the wireless set themselves ororganise school concerts or otheractivities to raise funds.

" In short, it is the teacher or thealready over -burdened parent whopays for this new branch of free '-education.

" We, as teachers, feel that it isbecoming increasingly incumbent onlocal authorities to provide this excel-lent ' mechanical aids to presenteducational equipment.

" Fortunately, a small proportion ofauthorities are already leading theway."

25 W.B. Speakers Given Free !See page 606.

Augtht 29th 1936

"A MARKED ADVANCE ONPREVIOUS MODELS


1937 STENTORIAN PRICESCabinet Models Chassis Models

37 SC (Senior) - 63'- 37 S - - 42'-37 JC (Junior) - - 49/637 CC (Cadet) - - 39'6

37 BC (Baby) - - 29'6

Duplex - - £6 6 0

37 J -

37 B -

37 M -

EWA/ -

Duplex -

- 37'6- 23'6- 17'6- 70/-

84' -

To the understanding eye the curves reproduced here (taken from1936 and 1937 Stentorian Senior models respectively) will conveymore graphically than any words the great stride forward thisnew design represents. Each, in a commercial speaker, is aremarkable achievement ; but a study of the 1937 type's improved

top response, absence of harsh resonances,and remarkable levelness leaves no roomfor doubt as to the magnitude of thisyear's improvement. Whether you arebuilding a new receiver or wish to revolu-tionise the performance of your presentset-hear the 1937 Stentorian and knowwhat 1937 reproduction can

YOU MAY NOW BUY THE STENTORIANSENIOR ON HIRE-PURCHASE FROM

YOUR DEALER t ASK HIM

Says Mr. F. J. CammW.B. Engineers are proud that an authority of

Mr. Camm's standing should immediately and soemphatically endorse their opinion of the new 1937Stentorian. Mr. Camm's message, reproducedbelow, gives sure proof that W.B. research in thepast year has by no means been in vain :-

" Once again I can confirm the claims of your engineersto have enhanced even further the already enviable reputationwhich your speakers enjoy. The 1937 Stentorian, which Ihave submitted to a thorough test, represents a markedadvance on your previous models. If anything, your claimsare too modest, for my curves show a greater degree of fre-quency response at both ends of the register. Last year Iasked, Can there be a better speaker ?' Your 1937Stentorian Speaker supplies the affirmative answer. Alllisteners, and particularly constructors, owe a debt of gratitudeto the indefatigability of your research engineers."

'la I aC411"46416416.°46.6.41".-

You should hear this latest W.B,product. Like Mr. Camm, you will atonce realise that here indeed is anothermilestone in loudspeaker progress.

SEE THEM AT RADIOLYMPIA

STAND 66

36 s

tuSSt,

wto...co Cram

41937 STENTORIANWHITELEY ELECTRICAL RADIO CO, LTD., MANSFIELD, NOTTS

Sole Agents in I.F.S. : Kelly & Shiel, Ltd., 47, Fleet Street, Dublin


BAN DS PREADShort -leave Thmet

Preliminary Details of an Efficient Three-valver Specially Designed for Short-wave Reception

DURING the past six months an in-creased interest has been taken inshort-wave reception. This is

mainly due to the fact that the televisiontransmissions are to be made on an ultra -short wavelength. The construction of atelevision receiver is too expensive a pro-position, for the average reader at present,but thou -Sands of our readers who havetaken no interest in short-wave listening arenow anxious to try their luck on the short-wave bands as a forerunner to televisionexperiments. We therefore decided toproduce two receivers capable of receivingtransmissions on wavelengths below 50metres. One, the Gladiator, is an all -wavemodel for the readers who want to make upan efficient receiver which any member ofthe family can operate with ease. It wasthought, however, that the short-waveenthusiast would require a set speciallydesigned for short-wave listening, havinga band -spread tuning unit for easy receptionof amateur transmissions.

the Circuit ArrangementAfter experimenting with several circuit

arrangements, it was decided that anefficient three -valve design would meet therequirements of most listeners. A fourthvalve would certainly increase the volume,but this increase would also be accompaniedby intensified background noise. Anexamination of the theoretical circuitarrangement will indicate that three pen-tode valves are used, one of the H.F. varia-ble mu type for H.F. amplification, astraight H.F. type as detector, and an L.F.type 'for the last stage.

Bandspread TuningSome readers may not approve of the

use of an untuned aerial stage. As band -spread tuning was considered to be essen-tial, however, the use of two tuned circuitswould tend to make_ receiver too com-plicated for beginners. The loss in efficiencydue to the use of an aperiodic aerial stageinstead of a tuned stage is not pronouncedas the amplification provided by the H.F.valve is very low on wavelengths below50 metres. By using one tuned stagetuning can easily be effected by means ofthe bandspread condenser operated inconjunction with the special tank con-denser. Readers who have not heard of theEddystone tank system of band spreadtuning will appreciate a few details. Thebandspread condenser C2 has a capacityof approximately 20 m.mfd., and is con-tinuously variable. Its fixed and movingvanes are connected across the fixed andmoving vanes of a semi -variable cOndenserhaving a capacity of 140 m.mfd. variablein steps of 14 m.mfd. A patented stopmechanism is incorporated so that the

minimum capacity can be set to a pre-determined value, the maximum capacitybeing then determined by the position of thelow capacity variable bandspread con-denser. This variable is provided with a9-1 slow motion drive, having a remarkablysmooth movement. The smoothness of thecontrol and the ease of tuning with thissystem has to be tried to be appreciatedfully.

Intervalve CoilThe coupling between the H.F. valve

and the detector constitutes an H.F.transformer coil. The lower end of theprimary winding of this coil is connectedto the earth end of the grid winding, and,therefore, a four -socket holder can beused, the H.F. valve cap being connectedto the top terminal of the coil. The caplead of the valve could, of course, bejoined to the coil terminal joined to thefixed vanes of the tuning condenser, butbetter results are obtainable when the coilis used as an H.F. transformer with thetop terminal in use. A .1 mfd. non -induc-tive condenser is joined between theearth end of the grid winding and themetal chassis so as to provide an effectivepath to earth and to the moving vanes ofthe tuning condenser.

Reaction CircuitIt is customary to upe a screen voltage

reaction control when an H.F. pentode isused as a detector, but experiments indicatethat it is difficult to obtain a potentiometerthat has a sufficiently silent movement toensure the absence of slight crackling whenthe control is operated. Some makes werefound to be quite satisfactory, but it isprobable that even the best ones wouldget noisy after a few months' use. Thecondenser control, on the other hand, issilent in action, and if the voltage appliedto the screen of the detector valve is care-fully chosen, very, smooth reaction controlcan be obtained.

CouplingResistance capacity coupling is used

between the detector and the output valveas the high efficiency of the pentode de-tector renders the use of an L.F. trans-former unnecessary. Resistance couplinghas the advantage of providing a moresilent background, and eliminates thecommon short-wave bugbear of thresholdhold-a very great advantage when usingheadphones.

Constructional and operating instructionsfor this fascinating receiver will be given

e

Panel layout of the Bandspread.

Jt"

= = = =

344

8"


next week. In the meantime there are, nodoubt, many who will prefer to commencework right away.The Chassis

The chassis is of the all -metal type, andmay be obtained ready -drilled and preparedfrom Messrs. Peto Scott, together with thespecial metal panel. Unless you areexperienced in metal work it will be wiseto obtain this complete chassis, as thebending of the chassis and the cutting ofthe large diameter holes for the valve -holders require some care and the use ofspecial tools.

All components which are attached to thechassis, as well as the metal panel, are heldin position by short bolts and nuts, and thesemay be obtained complete with the kit.It will be noted from the wiring diagram onthis page that the metal chassis is employedas an " earth return," that is to say, theH.T. negative supply to the receiver passesthrough the safety fuse and is then joinedto the chassis. The negative filament legof each valve -holder is then joined to one ofthe bolts which hold the valve -holders inposition, and in this way the circuit iscompleted back to the H.T. negative lead.This type of connection is not safe whenusing a wooden chassis of the metallisedtype, but when a substantial metal chassisis employed the disposal of the various con-necting wires not only greatly simplifiesthe constructional work, but also resultsin some slight gain in efficiency due to theimproved screening and the shortness ofcertain earth leads. This is particularlynoticeable in the case of H.F. decouplingcircuits, and where a long lead to earthmight result in some instability due tocoupling with other leads or - components,the direct earthed connection to the chassisavoids this trouble.

Wiring the ReceiverWhen all the components have been

mounted in the respective positions the

LIST OF COMPONENTS FORTHE BANDSPREAD S. -W. THREE.One short-wave coil, type B (Wearite).One bandspread tuning outfit C2, C3 (Eddy-

stone).One 50,000 ohm potentiometer R6 (B.T.S.).One air -dielectric pre-set condenser, Type

SW.87 C1 (Bulgin).Five fixed resistances (1 watt type) (Erie).50,000-1 RI. (Erie).100,000-2 R4, R5. (Erie).1 megohm-2 R2, R3. (Erie).Seven Fixed Condensers:One .0001, Type 665 C8 (Dubilier).One .001, Type 4501 C11 (Dubilier).One .01, Type 4501 C9 (Dubilier).Four .1, Type 4503 C5, C6, C7, C10 (Dubilier).One 3 -point on/off switch (B.T.S.).Four chassis -type valve -holders, 3 four -pin,

one 5 -pin (Clix).Two terminal Strips, aerial and earth and

loud -speaker (Belling -Lee).Seven wander plugs, H.T.-, H.T.1, H.T.2,

H.T.3, G.B.-, G.B.1, G.B.2 (Belling -Lee).Two spade connectors, L.T.- and L.T.-F

(Belling -Lee).One S.W. H.F. Choke, Type H.F.3 (Bulgin).One Type RC32 reaction condenser (B.T.S.).One loud -speaker, Type 37M. (W. B.).One pair headphones (Ericsson).One Microfuse with Holder (100 m/A).One Bandspread Three Cabinet Peto-ScottOne metal chassis 10in. by nin. by 21in.

(Peto-Scott).Three valves, Types HP211, HP2I0 (4 -pin),PP222 (5 -pin) (Tungsram).

« mi

wiring may be commenced. Use a fairlyheavy gauge wire, and either the " slip -back " type or one of the glazed cotton -covered wires will be found suitable. The

former is the simpler, as it is only necessaryto scut off the necessary length and pushback the insulated covering in order to makethe connecting loop. With the glazed type

WIRING DIAGRAM OF THE It) ANDSPREADSHORT.WAVE THREE

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L. 3'

rreeyZEADs .474.rsZ7i.eouem eueeE,e BUSH.

E.- A

E A

/W. C = METAL CNASS/S.

1937 STENTORIANALL MODELS OVER 3916 ARE AVAILABLEON H.P. TERMS FROM YOUR DEALER


of wire, the covering must first be scrapedaway, and in the past we have found manycauses of breakdown due to the manner inwhich this has been carried out. If a verysharp knife is used and is run round the wirewith much pressure, not only will the in-sulated covering be cut through, but theknife will also penetrate the actual, wire fora short distance. The result is that whenthe wire is anchored beneath the screw -head or terminal, after a very short whilethe wire will break right through, althoughit may be held in position. The result willbe noises and perhaps a complete break-down in this part of the receiver. Therefore,when scraping away this covering use theknife in a more flat position, and any loosecotton ends which may remain may easilybe removed by the simple expedient ofburning them off with a match. Theinsulated covering is heat proof and a neatend to the lead will be obtained free from" whiskers."

If a loop is made for insertion beneath aterminal head or nut, make quite certainthat the loop is made in a clockwisedirection. If this precaution is not takenthe loop will open when the nut is tightened.'As a further precaution in this connection,the loop may be " sandwiched " betweentwo washers.

Soldered ConnectionsThe resistors and condensers used in the

receiver are of the wire end type, and theactual wire ends are employed for con-necting purposes in most cases. These maybe cut down where necessary in order tokeep the component in position, and in oneor two cases the wire must be lengthened.When soldering the additional lead to theresistor do not leave the soldering iron in

long a period or the valueof the resistor may be modified. Similarly,the leads to the condensers may be loosenedby a long application of the iron, andalthough the lead may not come away,an internal disconnection will prevent thereceiver from functioning in certain cases.Condenser C8 is suspended in the wiring,and the metal ends of is must be pre-vented from coming into contact with the,chassis. A stiff and very short length ofwire joined to the grid terminal of the valve -

holder of V2 will assist in this direction, andthe lead which passes through hole No. 4may be taken over condenser C7 to assistfurther in this direction.

Operating InstructionsIt is not intended to give full operating

instructions this week, but for those who

have sufficient of the components handyor who are able to obtain the parts at onceand complete the receiver, the followingbrief details will enable the receiver to beput into commission. First of all; the aerialto be used should be of the type designedfor good short-wave reception. Goodinsulation is one of the main features, andthe length may also be found critical insome cases. Experiment will enable asuitable arrangement to be found. When thereceiver, is switched on the main tuning iscarried out by adjusting condenser C3to the first of the " stops " on the controlknob, and then turning condenser C2

August 29th, 1936

through its entire range. Reaction shouldbe kept advanced to such a position thatit is just off the oscillation point. If nostation is heard when condenser C2 isreturned to its original position,the control on C3 should beturned to the next stop and

The completed BandspreadShort-wave 'Three.

the same procedure again gone through. Itthus be seen that at each stop or section

of C3 the condenser C2 is employed as a ver-nier device and divides up the tuning scaleinto a further narrow band. It is due to thiseffect that the term " band -spreading " isemployed. If the reaction control (C4) isadvanced too far the receiver will fall into' astate of oscillation, and it will not be possibleto hear telephony' signals. C.W. or con-tinuous -wave morse signals would then beheard, however, and these will appear in theform of a loud whistle or chirrup.

TO OUR READERS-AND THE TRADE (Continued from por 603)

unsatisfactory components have been issued to the public,and it is my fervent hope that this will not be the casein the ensuing season. A beginner who is disappointedin this way deserts home construction, and you havelost a customer, we a reader.

Each year a new generation of home constructorssprings up, and we endeavour to produce designs satis-factory in performance, but simple in construction, tosupply their needs. It is not unreasonable to ask you toencourage their interest by taking the greatest possibleprecaution to see that unsatisfactory components do notreach the market.

To new readers may I say that this is not a normalissue. Many of our regular features have been un-avoidably held over because of the justifiable claim uponour space made by the Show Report. Normal issuescontain a fair blending of every radio interest-a short-wave section, a beginners' supplement, summary of ourblueprint service, an up-to-the-minute news section, thevery latest news from the field of television, constructionalarticles on coils, transformers, chokes, and other com-ponents, constructional details of receivers perfected inour laboratories, free gift blueprints at regular intervals,

interesting replies to readers' letters, and a wide varietyof general radio subjects.

This journal has been responsible for the great revivalin home construction which has taken place duringthe past four years. It has introduced some radicalchanges, such as metallised chassis, transfer print wiringdiagrams, service data sheets' of our receivers, free repliesto, readers' questions, the specification of only thoseparts which were used in our original designs ; outseries of technical volumes, many of which have beentranslated into several languages, have a sale far greaterthan any other volumes of similar character-the salesrunning 'into millions. It is a matter of gratification tous who serve your interests that we have earned thereward of your continued loyalty to this paper. Thememorial stones to this are those of our contemporarieswho have fallen by the wayside.

During the season which follows we shall introduce manynew features and surprises of far-reaching effect. May Iadd that I shall welcome on our Stand No. to on theground floor any reader who calls upon me ; my staff willalso welcome you. It is the one occasion in the year whenreaders, staff, and Editor may meet on common ground.

Yours faithfully,THF., EDITOR.

August 29th, 1936

AERIALITE, LTD., Junction Mills, WhittingtonStreet, Ashton-u.-Lyne. Stand No. 9

THE specialities exhibited on this stand will consistof aerial accessories, such :IS the 7 -strand and.

11 -strand Sqper Aerial Wire, and the " Trapeze,"and Di -pole aerials. A special interference -freematched di-noie aerial kit will also be seen, together

ith many accessories for the erection of neat and

The neat speaker opening and single externalcontrol employed in Beethoven Model RS. 827.

efficient aerial systems. In addition, tricklechargers, eliminators and loudspeakers willalso be shown, whilst some special Short-wave Adaptors, for either battery or maimuse will be a prominent feature.AERODYNE RADIO, LTD., Aerodyne Works,

Tottenham, N.17. Stand No. 74AN interesting range of receivers will be

shown here, running from a simplebattery three-valver to a super -sensitive 5 -valve mains set. Most of the models are of the all -range type, covering the short wave -bands inaddition to the normal broadcast bands. Model 54wiU prove attractive on account of the uniqueSpear-o-lite tuning indicator which is fitted and whichindicates by means of an illuminated arrow the exactstation and wavelengthto whichthereceiver is adjusted.The large tuning dial which is fitted to the Aerodynereceivers greatly simplifies tuning and gives thereceivers a very attractive appearance.AERONAUTICAL AND GENERAL INSTRUMENTS,

LTD., Purley Way, Croydon. Stand No. 30.ALL POWER TRANSFORMERS, LTD.,8a, Gladstone

Road, Wimbledon, S.W.19. Stand o. 206AN extensive range of mains accessories, including

transformers and chokes, will be featured bythis company. In addition, output and intervalvetransformers, employing special core materials, willalso be on view. The production- of television equip-ment and high-powered public address equipment hasalso led to a demand for high -voltage mains accessories,and many of these will be on show on this stand.


Complete Guide I

to the ExhibitsIn some eases details of exhibits have not been

released at the moment of going to press.

Some new lines will include special high -voltage,low -amperage maim transformers for feeding cathode-ray equipment, and also some high-fidelity amplifiersgiving 10 watts output. Special components designedfor tzopical use will also be on view.ARMSTRONG MFG. CO., 100, King's Road, Camden

Road, N.W.1. Stand No. 224.AUTOMATIC COIL WINDER AND ELECTRICAL

CO., LTD., Winder House, Douglas Street, S.W.1.Stand No. 31T port ion of the exbil,its on this stain] will

.1 instrument, of all types,

A new split anode circuit connector produced by Messrs.Belling and Lee.

These will include the very popular Avometer andAvonduor, as well as some new instruments such asthe Capacity Meter and a new 46 -range UniversalAvometer. An improved Signal Generator will alsobe seen for the first time, and Service Engineers andadvanced experimenters will be interested in thisand the Avo-Oscillator, which are valuable adjunctsto the testing of receivers. A new machine designedfor the simultaneous winding of coils with paper in-sertion and final parting off on completion will also beshown, and this has variable speeds from 500 to 3,000r.p.m. and winds up to 12 coils at a time.BALCOMBE, A. J., LTD.,52-58, Tabernacle Etreet,

London, E.C.2. Stand o. 41THE Alba receivers to he seen on this stand will

range from a 6 -guinea 3 -valve battery set to

Floor Plan appears on page 627.Bus and other Transport Facilities elimination of mains noises. These cover practically

page 629. every type of interference and may be applied to"Stand -to -Stand" Report next w ek. practically every piece of apparatus or wireless receiver.

A new aerial kit for the suppression of noises introduced

623

a 27 -guinea A.C. automatic radiogram. The lattermodel possesses several novel features and is a neatand attractive piece of cabinet work. The circuitemployed consists of an 8 -stage superhet with a wave -range from 19.5 to 2,000 metres, the lower rangeending at 50 metres. The large tuning scale is alsofeatured in the Alba receivers, and to indicate tuningpositions the "Searchlight" tuning device is fitted,and a cut-off switch is provided for switching off thelight when the receiver is tuned in the battery models,in order to avoid an undue drain on the battery.

BARR ATT & ROBINSON, LTD., 288, York Road,King's Cross, N. Stand No. 226.

BEETHOVEN RADIO, LTD., Chase Road, North Acton,London, N.W.10. Stand No. 34THE Baby Portable will attract considerable

attention on this stand, as it is one of the smallestcommercial portables to be produced. Measuriagonly Dins. by 8bins. by 5ins. and weighing only 10lbs.,this interesting little receiver comprises a standar.14 -valve circuit (using full-size valves) and incorporatesa 70 -volt H.T. battery and an accumulator givingtwenty hours service per charge. It costs £6 6s. Inaddition there will he several other portables on view,

: as well as the- alligglidatvo,parttet radiogram, in a'two-tone French WRIbut cabibet costing 25 gas.,which is shown on thig page.

BELLING AND LEE, LTD., Cambridge Arterial Road,Enfield, Mddx. Stand No.98

IN addition' to the multitude of small accessoriessuch as wander plugs, connectors, leads, etc.,

featured by this firm, there will be many interesting

The novel tuning indicator on this Beethoven Model 99recover greatly simplifies tuning.

Suppressing devices for use in connection with the


from the aerial side of the receiver will also be exhibited,and a special exhibit will consist of the InterferenceMeasuring Set, which has been built by Messrs. Bellingand Lee to Post Office Specification and which measuresthe interference voltage and enables the preciseeliminating equipment to be chosen.

BENJAMIN ELECTRIC, LTD., Brentwood Works,Tariff Road, Tottenham, London, N.17. Stand No. 91.

UNDOUBTEDLY the main attraction on the Ben-jamin stand will be the new Duode loudspeaker.

This is a high -quality speaker and the inventor willbe in attendance to describe its main features andto answer questions in relation to its performances,etc. Other Magnovox speakers will also be shown,and in addition many of the small Benjamin productssuch as vaiveholders, switches, transformers, chokes,etc., which have for a long time proved very popularwith the home -constructor.

BRIDGER & 'CO., LTD., R.O., No. 4, Factory, Shel-ford Place, Church Street, N.16. Stand No. 211.

BRITANNIA BATTERIES, LTD., Union Street, Red -ditch, Worcs. Stand No. 71THE main portion of the exhibits on this stand

will consist of Pertrix batteries. These are ofthe non -sal -ammoniac type; and in addition there willbe some neutral electrolyte refill batteries for flashlights, cycle larbps and torches, Pertrix accumulatorsfor L.T. purposes, as well as a full range of Bulldog(Sal -ammoniac) dry batteries for H.T. purposes. It isinteresting to note that as each commercial receiver isproduced a new Pertrix battery is also producedspecially designed to fit it. There is thus always' aPertrix battery available for the popular makes ofreceiver.

BRITISH N.S.F., CO., LTD., Wadden Factory Estate,Croydon, Surrey. (See Wingrove & Rogers).

BRITISH G.W.Z. BATTERY CO., LTD., FalmouthRoad, Trading Estate, Slough. Stand No. 69.

BRITISH PIX CO., LTD., Pix House, 118, SouthwarkStreet, London, S.E.1. Stand No. 209THE Pix Indoor Aerial is, of course, already very

popular and will be well displayed on this stand.in addition the various other aerial accessories, such asthe Grippon fitting, which is illustrated below,

The novel Crimson Aerialdevice to be shown by

British Pix, Ltd.

and the lightning arrestor and selectivity device willalso be well featured. Pix Valves, the Pix MetallisedEarth, the Hydrolyte Earth Conductivity Compound,and the Modals Armchair Control are other accessorieswhich will go to make up a very attractive display,and they are all accessories which will appeal to thelistener who is out to get the best from his receiver.

BRITISH ROLA CO., LTD., Minerva Road, Park Royal,N.W.10. Stand No. 93THE display of loudspeakers on this stand will

include no fewer than eighteen separate models,ranging from the miniature model suitable for thelightweight portable, to the large 12in. diameter 0.12fidelity speaker shown on this page. This particular

model will take pride of place and will attract everyonewho is looking for the latest in loudspeaker design.Another outstanding model in the Rola range is theRoma (also illustrated), specially designed to cover allextension speaker requirements. This is an Sin.speaker housed in a handsome walnut cabinet, andfitted with two low- and two high -impedance terminals.By placing a wander plug in the correct socket exactmatching with any receiver can be secured. Ifdesired, the speaker used in this model may be obtainedwithout the cabinet.

B RITISH TUNGSRAM RADIO WORKS (GT. BRITAIN),LTD., 72, Oxford Street, W.1. Stand No. 33.

A FULL range of valves including some novelI-% power valves for mains use will be seen onStand 33. A new Universal vari-mu ILL. pentode willbe shown as well as a slew triode-hexode.

BROWN BROS., LTD., Gt. Eastern Street, E.C.Y.Stand No. T8.THIS will be purely a wholesaler's exhibit and

representative models of various well-knownmakes will be seen.

B ULGIN & CO., LTD., Abbey Road, Barking, Essex.Stand No. 1.

THE name of Bulgin needs no introduction, and therewill probably not be another stand in Olympia

with such an extensive range of components designedfor the home constructor. Ranging from a selection of

SITTING TOWALLS 1.-5.IN THICKNESS

Two of the many new Bulgin accessories :phi, h 11).11

be on view on Stand No. 1

control knobs costing only a few pence each, thisextensive range will embrace such items as tuning coils,condensers, resistances, transformers, connectors,chokes, fuses, solder, instruments, neon lamps, aerialkits, etc. The two illustrations on this page shownew lines which will be seen at Olympia for the firsttime and these include pre-set condensers, Vibratortype H.T. transformers, midget split -secondarytransformers, chokes, Meter Push controls, lead-ininsulators, flexible shaft couplings, valve -holders, andRelays.

BURGOYNE WIRELESS (1930), LTD., Great WestRoad, Brentford, Mddsx. Stand No. 75.

FOR the first time Messrs. Burgoyne Wireless willbe showing all -wave receivers, and some striking

all -wave receivers and radiograms will be exhibited.A five -valve superhet tuning down to the S.W. bandfrom 19 to 55 metres will form an attractive centre-piece for the remaining battery and mains receivers,and the straight circuit incorporating four -valveswith Litz wound coils will also prove very interesting.An interesting point with regard to the Burgoynesuperhet is that the intermediate frequency whichhas been selected is 473 kc/s.

BURNDEPT, LTD., Light Gun Factory, Erith, Kent.Stand No. 65.

THE twin -speaker Ethodyne will fbrm an importantexhibit on the Burndept stand, and will be

backed up by various battery and mains receivers,at prices ranging from t5 38a. 6d. to 131 gns.. and

cover a three -valve portable,four -valve band-pass receiverand the A.0Mains Max -Specification2 -Band super -het. Two newall -wave re-ceivers areintroduced un-der the title ofFour -bandband-pass and itshould be

August 29th, 1936

The new RolaG.12 Speakerand RomaE x tension

model

noted that only two very narrow bands are omittedfrom the complete coverage from 13.5 to 2,000metres. One receiver is for bath, y use and theother for Universal mains.

BUSH RADIO, LTD., Woodger Road, Shepherd's BushW.12. Stand No.50.

AMONG the Bush receivers will le a seven -stagesuperhet with nine tuned circuits covering four

separate wavebands. The same chassis is included inmodel R.G.33, which is a radio gramophone fitted witha 12in. moving -coil speaker. Various other interestingmodels will be shown, and a feature of the Bush setsis the double pointer on the rectangular tuning scale,which shows every setting of the tuning condenser.In the radiograms the lid la split so that either halfmay be raised at will, and thus when only the radio isrequired it is unnecessary to uncover the turntable.

CADISCH & SONS, R., 5-6, Red Lion Square, W.0.1.Stand No. T10.

THIS also will be a wholesale exhibit showingrepresentative commercial receivers.

CELESTION, LTD., London Road, Kingston -en -Thames. Stand No. 24.

THE display on this stand will consist of a completerange of permanent and energised magnet -type

loudspeakers. These will include cabinet and chassismodels, together with one new cabinet speaker whichwill be known as the Junior 8 model. This is fittedwith a fully universal transformer and a constantimpedance volume control. The cabinet is of figuredwalnut, and the tappings on the transformer make itpossible to match this speaker to any receiver bramplifier.


ENCYCLOPEDIABy F. J. GAMIN 4th 5if(Editor of ... Practical Editionand Amain:, Wireless- ) not.

Wireless Construction, Terms, andDefinitions explained and illustrated

in concise, clear language.

From all Booksellers, or by post t/6 fromGeorge Names, Lid., 8-11, Southampton

Street, Strand, London, W C.2.

August 29th, 1936

CHLORIDE ELECTRICAL STORAGE CO., LTD.,Exide Works, Clifton, Junction, Nr. Manchester.Stand No. 32,

ANextensive range of batteries for all purposes will1-1 'be shown by the makers of the popular Exide andDrydex components, and the latest development in


An H.T. accumulator unit from the Exide range.

L.T. accumulators is the Exide " Hycap " cell, anillustration of which appears 'on this page. "Thisbattery has been designed to cope with the increasedcurrent consumption of the' modern hig1Gpowerreceiver. The popular visible charge indicator is in-corporated. A stack -type wood crate has also beenproduced this year for the H.T. accumulators, and anillustration of this is also given. There are now morethan 150 different types of Drydex dry battery, andthese will form an attractive display.

CITY ACCUMULATOR, CO. 'LTD., 18-20, NormanI Buildings, Central Street, Stand No. 18.

addition to the various receivers to be seen on1 this stand, an interesting item, will be the all -wave set of coil units, complete with screens, wave -change switch, I.F. transformers, I.E. and local stationfilters, etc. These are supplied ready with the neces-sary fittings for inclusion in a normal chassis andwill greatly simplify the construction of an all -wavesuperhet. The two new receivers include the " Coro-nation" model shown on this page, which is a six -valve A.C. receiver, incorporating scanning -disc tuning

COLE, E. K., LTD., Ekco Works, Southend-on-Sea.Stand No. 63.THE chief attraction on the Ekco stand will un-

doubtedly be the " batteryless " battery receiver.In this, by means of a novel device, the H.T. batteryhas been dispensed with, and the necessary high-tensionsupply is obtained from the L.T. accumulator. Otherinteresting details concern the moulded cabinets, andthe interesting designs of Serge Chermayeff in blackand ivory will no doubt set a new note in receiverdesign. High fidelity is also an important feature ofthe Ekco receivers, and a special filter is now ineor-'pgrated in the Ekco receivers to prevent interferencefrom tWo neighbouring stations, and an extremelyresponsive speaker gives improved reproduction.

COSSOR, A. C., LTD., Cossor House, Highbury Grove,N.5. Stand No. 55.

I N addition to an extensive range of completereceivers, the Cossor stand will undoubtedly

feature valves, cathode-ray tubes, and similar equip -

ment. The complete range of Cossorvalves will be made into an attidt-tive display., and the. cathode-raytube, owing to it's increased popu-larity due to television, will attractconsiderable attention. A Ganging

-Oscillator,`a` PortableOsqillwaph, and somecomplete teievidion equip-ment will' also be exhibi-ted, and the ingeniousdesign of the completestand (following the linesof a Moroccan Palace) willmake this exhibit a mostattractive one.

CRYPTON EQUIPMENT,LTD., North ActonRoad, Park Royal,N.W.10. Stand No. 202ACOMPLETE range of

battery chargers willform this exhibit and willappeal chiefly to thedealer and serviceRotaryman.-transformers,switchboards, rectifiensand all allied equipmentwill bd included.

COSMOCORD, LTD.,Cambridge Arterial

Road, Enfield, Middx. Stand No.78.THE neat Unigram Playing Desk,

illustrated last week, is amodification of the unit which hasalready been seen before and whichhas proved very attractive. It con-verts any table -type receives' into an

Note the novel tuning scab on this 4 -band Bush receiver.

DAVIS & TIMMINS, LTD., Brook Road, Wood Green,N.22. Stand No. 210.

The Hycap Exide Model C. F. G. 9.

efficient radiogram, and is designed for use with A.G.mains. It comprises a powerful induction motor, newCosmocord pick-up, volume control and speed regulator,and it will be Shown, together with the separateCosmocord components, on this stand.

COLLARD,

Cossor's popular receiver. has an interesting cabind design.

LTD., Culmore Works, Culmore Road,Peckham, S.E.15. StandNo. 70.

TURNTABLES, pick-ups andapplied gramophone appara-

tus will be exhibited on thisstand, and a new automaticrecord changer will form themost important feature. Inaddition, a new A.C. inductionmotor, and a Universal motor,will 'be included, together withsome complete radiogram units.For those with no mains facili-ties, some spring gramophoneunits will be on view, and thesewill appeal to every enthusiastwho wishes to build a radio-gram.

DALLAS & SONS, LTD., J. E.,Dallas Building, Ridgmoun,Street, London, W.C.1. StandNo. T23.

THE exhibits on this standwill cover all the popular

makes of complete receivers,valves, batteries, components,etc., and as factors, Messrs.Dallas will provide an attrac:tive comprehensive display.

'it

D. M. DAVIES WOODWORK, Trading Estate, Slough,Bucks. Stand No. 17.

DECCA GRAMOPHONE CO., LTD., 1-3, Brixton Road,London, S.W.9. Stand No. 44.

THE range of Decca receivers extends from a simplebattery three-valver to an elaborate A.C. mains

auto -changer radiogram with six valves. The rangeof instruments will also include a mains portable radio-gram and a mains gramophone attachment. Many ofthe new models incorporate the Selectorlite dial, a newfeature to simplify tuning.

DENT, R. H. (Ardente), 309, Oxford Street, W.1.Stand No. 3.

ACOMPLETE range of the latest and most advanceddesigns in public-address equipment will once

again be on show at this stand. One of the moatoutstanding attractions on view will be the newArdente Dynamic Ribbon microphone. This attrac-

One of the new

1.1

1937 C. A. C. receiversning Disc tuning.

(4:1

with Scan-

626 PRACTICAL AND AMATEUR WIRELESS AugUst 29th, 1936

Full List of Exhibitors arranged in AlphabeticalOrder, with Addresses and Stand Numbers.

z

-e-CX1-1111BITOR\S7

NAME ADDRESS STAND NO. NAME ADDRESS STAND NO. NAME ADDRESS STAND NO.Aerialite, Ltd., Junction Mills, Whittington

Street, Ashton-u.-Lyne 9East London Rubber Co., Ltd., 29, Great Eastern

Street, E.C.1 T9Multitone Electric, Ltd., 95, White Lion Street,

Islington, N.1 .. 86Aerodyne Radio, Ltd., Aerodyne Works,

Tottenham, N.17 74Eavestaff Co., Ltd., Autoplayer Factory, Ashfleld

Road, N.4 225 New London Electron Works, Ltd., East Ham,Aeronautical & General Instruments, Ltd., Econasign Co., Ltd., 92, Victoria Street, S.W.1 222 E.6 22

Purley Way, Croydon, Surrey.. 30 Edtkon Swan Electric Co., Ltd., 155, Charing Nomnes, Ltd., (Worm 8-11, Southampton Street,All Power Transformers, Ltd., 8a, Gladstone Cross Road, W.C.2 .. 42 W.C.2 .. 10

Road, Wimbledon, S.W... .. 206 Efficiency Magazine, 87 Regent Street, W.1 .. 221Armstrong Mfg. Co., 100, King's Road, N.W.1. .Automatic Coil Winder & Elec. Equipment Co.,

Ltd., Winder House, Douglas Street, S.W. ..

224

31

Ensign, Ltd., 88, High Holborn, W.C.1Epoch Reproducers, Ltd., Aldwych House,

Aldwych, W.C.2 . ..Ever Ready Co. (G.B.), Ltd., Hercules Place,

T22

94

Partridge Wilson & Co., Ltd., Evington ValleyRoad, Leicester

Philips Lamps, Ltd., 145, Charing Cross Road,W.C.2

107

43

Balcombe, Ltd., A. J., 52, Tabernacle Street,

Barratt & Robinson, Ltd., 288, York Road,King's Cross, N...

41

226

Holloway, N.7 -Everett Edgcumbe & Co., Ltd., Colindale Works,

Hendon, N.W.9 ..Farrex Radio, Rear of 543, Holloway Road, N.19

58

213

218

Plessey Co., Ltd., Vicarage Lane, Ilford, Essex ..Primographie, Ltd., 40-44, Chipstowe Street, W.1Primus Mfg. Co., Ltd., Primus House, Willow

Street, E.C.2

27223

lABeethoven Radio, Ltd., Chase Road, North Ferranti, Ltd., Radio Works, Moston, Manchester Prism Mfg. Co., California Works, Brighton

Acton, N.W.10 34 8, 63, 216 Road, Belmont, Surrey 80Belling & Lee, Ltd., Cambridge Arterial Road, Film Industries, Ltd., 60, Paddington Street, W.1 4 Pye Radio, Ltd., Radio Works, Cambridge 48

Enfield . . 98 Flinders (Wholesale), Ltd., 14-20, St. Peter's ..Benjamin Electric, Ltd., Brantwood Works,

Tariff Road, N.17Bridger & Co., Ltd., R.O., No. 4 Factory,

Shelford Place, Church Street, N.16..

91

211

Street, Ipswich .

Fuller Accumulator. Co., Ltd., Woodland Works,Chadwell Heath, Essex.. .. ..

T16

101Radio Gramophone Development Co., Ltd.,

18-20, Frederick Street, Birmingham ..Radiometers, Ltd., Dunbar Works, Dunbar

56

Britannia Batteries, Ltd., Union Street, Redditch, Garrard Engineering & Manufacturing Co., Ltd. Street, West Norwood, S.E.27 20371 Newcastle Street, Swindon, Wilts. _ 37 Radio Resistor Co., Ltd., 1, Golden Square,

British Broadcasting Corpn., Broadcasting General Electric Co., Ltd., Magnet House, Piccadilly, W.1 10House, W.1 38, 67

British G.W.Z. Battery Co., Ltd., FalmouthRoad, Trading Estate, Slough .. 69

British N.S.F. Co., Ltd., Waddon FactoryEstate, Croydon, Surrey 96

British Pix Co., Ltd., 118, Southwark Street,S.E.1 209

Kingsway, W.C.2.. . . 40,Gilbert" & Co., Ltd., C., 73, Arundel 'Street,

Sheffield -.. ..Goodmans (Clerkenwell), *Ltd.; Broad Yard

Works, Turnmill Street, E.C.1 .

Gorst Electrical Co., Ltd., Portadyne Works,Goret Road, N.W.10 .

51

T14

87

46

Radio Society of Great Britain, 53, VictoriaStreet, S.W.1

Rawlplug Co., Ltd., Rawlplug House, CromwellRoad, S.W.7

Reproducers & Amplifiers, Ltd., FrederickStreet, Wolverhampton

214

79

92British Role Co., Ltd., Minerva Road, Park

Royal, N.W.10 .. 93Gramophone Co., Ltd., di, Cleikenwell Road,

E.C.1 54Rists Wires & Cables, Ltd., Freemantle Road,

Lowestoft 208British Tungsram Radio Works, Ltd., West

Road, Tottenham, N.17 .

Brown Brothers, Ltd., Great Eastern Street,E.C.2 .

33

T8

Grampian Reproducers, Ltd., Station Avenue,Kew Gardens, Surrey

Hacker & Sons, H., Perfecta Works, Ray Lea

21Rothermel, Ltd., R. A., Rothermel House, Canter-

bury Road, N.W.6 89

Bulgin & Co., Ltd., A. F., Abbey Road, Barking,Essex .. . 1

Road, Maidenhead . .Harmer & Simmons, Ltd., 223, Hoe Street,

29 Selecta Gramophones, Ltd., 81, SouthwarkStreet, S.E.1 T11

Burgoyne Wireless, Ltd., Great West Road, Walthamstow, E.17 217 Self -Changing Gramophones, Ltd., 11, BerkeleyBrentford, Middx. .. 75 Harries Thermionics, Ltd., Avenue Chambers, Square, W.1 59

Burndept, Ltd., Light Gun Factory, Erith, Kent 65 Vernon Place, W.C.1 Shaftesbury Microphones, Ltd., 24, AldersgateBush Radio, Ltd., Woodger Road, Shepherd's Haynes Radio, Queensway, Enfield, Middlesex 13 Street, E.C.1 99

Bush, W.12 60 Heayberd & Co., F. C., 10, Finsbury Street, E.C.2 25 Siemens Electric Lamps & Supplies, Ltd., 39,Henderson's Wholesale Electrical & Radio, Ltd., Upper Thames Street, E.C.4 00

Electric House, Queen's. Road, Brighton .. T17 Sound Sales, Ltd., Marlborough Road, UpperCadisch & Sons, R., 5.6, Red Lion Square, W.C.1 T10 Henley's Telegraph Works, Co., Ltd., W. T., Holloway, N. .. 70Celestion, Ltd., London Road, Kingston -on - Holborn Viaduct, E.C.1 28 Stratton & Co., Ltd., Eddystone Works, Broms-

Thames .. .. 24 High Vacuum Valve Co., Ltd., 113, Farringdon grove Street, Birmingham .. . 23Chloride Electrical Storage Co., Ltd., 417 Bat- Road, E.C.1 26

tersea Park Road, S.W.11City Accumulator Co., Ltd., 18, Normans Build-

ings, Central Street, E.C.1 .

Cole, Ltd., E. K., Ekco Works, Southend-on-SeaCollaro, Ltd., Culmore Works, Culmore Road,

Peckham, S.E.15Cosmocord, Ltd., Cambridge Arterial Road,

Enfield, Middx. .. ..Cossor, Ltd., A. C., Cossor House, kighbury

Grove, N.6 .

Crypton Equipment, Ltd., North Acton Road,

32

'1853

70

78

55

Hillman Brothers, Ltd., 123, Albion Street, LeedsHobday Brothers, Ltd., 21, Great Eastern Street,

Invicta Radio, Ltd., Parkhurst Road, N.7 ..Ismay Distributors Ltd., Sterling Works,

Dagenham Jackson Brothers, Ltd., 72, St. Thomas Street,

S.E.1

T3

T20

35

73

81

Tannoy Products, Canterbury Grove, W. Nor-wood, S.E.27

Telegraph Condenser Co., Ltd., Wales FarmRoad, North Acton, W.3

The 362 Radio Valve Co., Ltd., Stoneham Road,Upper Clapton, E.5

Thompson, Diamond & Butcher, 34, FarringdonRoad, E.C.1 . .

Tucker Eyelet Co., Ltd., George, Cuckoo Road,Birmingham, 7 ..

45

68

207

T4

105Park Royal, N.W.10 .. 202 Kingsway Electricals, Ltd., 3-9, Dane Street,

88 Ultra Electric, Ltd., Western Avenue, Acton, W.3 52Dallas & Sons, Ltd., John E., Dallas Building,

Rldgmount Street, W.C.1 T23Kolster-Brandes, Ltd., Cray Works, Sidcup,

Kent 57Union Radio Co. Ltd., U.R. Works, Aurelia

Road, Croydon .. .. 20Davies Woodwork, D. M., Trading Estate, Slough,

Bucks. 17 Lectro-Linx, Ltd., 79a, Rochester Row, S.W.1.. 82 Varley, Cambridge Place, Bunage Road, S.E.18 77Davis & Timmins, Ltd., Brook Road, Wood L.E.S. Distributors, Ltd., 15, Alfred Place, Vidor, Ltd., West Street, Erith, Kent .. 61

Green, N.22 210 Tottenham Court Road, W.C.1 T21Decca Gramophone Co., Ltd., 1-3, Brixton Road,

8.W.9De La Rue & Co., Ltd., Thos., 00, Shernhall

44Linguaphone, Ltd., 24-27, High Holborn, W.C.1Lissen, Ltd., Worple Road, Isleworth, MiddlesexLondon Electric Appliances, Ltd., 62, Glengall

10664

Waterhouse, Ltd., Frederick, Stanley Works,Edward Street, Dudley Hill, Bradford

Webber & Co., Ltd., J. M., 39, Great Eastern201

Street, E.17 Road, Old Kent Road, S.E.15 212 Street, E.C.2 . T13Dent, IL H. (Ardente), 309, Oxford Street, W.1 3 Lugton & Co., Ltd., 203, Old Street, E.C.1 T5 Westinghouse Brake & Signal Co., Ltd., 82,Dew & Co., Ltd., A. J., 33, Rathbone Place, W.1 T6 York Road, Kings Cross, N,1 36Dibben, Ltd., Horace, 34, Carlton Crescent,

Southampton ..Diggle & Co., Jane Street, Rochdale .. ..

T1515

Manufacturers' Accessories Co. (1925), Ltd., 85,Great Eastern Street, E.C.2

Marconiphone Co., Ltd., 210, Tottenham CourtT7

Weston Electrical Instrument Co., Ltd.,Kingsto,nBy -Pass, Surbiton, Surrey ..

Wharfedale Wireless Works, 62, Leeds Road,215

Dubilier Condenser Co. (1925), Ltd., Ducon Road, W.1 49 Bradford .. 204Works, Victoria Road, North Acton, W.3 .. 89 McMichael Radio, Ltd., Danes Inn House, 265, Whiteley Electrical Radio Co., Ltd., VictoriaDulcetto-Polyphon, Ltd., 2-3, Newman Street, Strand, W.C.2 47 Street, Mansfield, Notts GE

Dyson & Co., Ltd., J., 5, Godwin Street, Bradford

&stick & Sons, J. J., 118, Bunhill Row, E.C.1

T19T2

T24

Milnes Radio Co., Ltd., Church Street, Bingley,Yorks ..

Mullard Radio Valve Co., Ltd., Mullard House,Charing Cross Road, W.C.2

205

62

Wingrove & Rogers, Ltd., Arundel Chambers,188, Strand, W.C.2

Wright & Weaire, Ltd., 740, High Road, Totten-ham, N.17

95

07


FINDING YOUR WAY ROUND RADIOLYNTIAFloor Plans Showing Positions and Numbers of Stands

91

92

93

94

95

96

97

226

225

15

82 81

14ILI El=

22 23

36

40

51

54

65

69

80 79

199 100 101 102 r

T14T13

24 25

41

50

55

64

70 71

78 77

103 104.

'PRACTICAL 8 AMATEUR WIRELESS")

26 27

34

42

49

56

63

1 76

GROUND FLOOR PLAN

711 T10 T9

RADIOINTERFERENCE

BUR EAU

T8 T71

8

28 29

33

43

INFORMATION

52

74

16 TS

THEATREBOOKINGOFFICE

T4 T3 T2

7

44

46

INTERPRETER

61

TORADIO

THEATRE

TI

205

Make a Note of It !" Practical and Amateur Wireless," the Leading WirelessJournal with the Largest Net Sales, is on sale at Stand No.10, Ground Floor, with its stable companions, " PracticalMechanics " (6d. monthly), " Practical Motorist " (3d.every Friday), and " The Cyclist " (2d. every Wednesday).Full range of our standard works on Wireless, Blueprints,etc., are also on sale.

T6 T17 T18 T19

GALLERY PLAN

T23

;ti 222

T24T 25 T 26

PROGRAM tAEDIFFUSION CCUIPOENT

59107

60

i2 o1

P 1106

214

215

216

217

218

ADDISON

ROAD

ENTRANCE

et


Give instrument, which has been tested and highlypraised by many authorities, is claimed by the Ardentelaboratories to be the greatest advance ever made inmicrophone technique.

The " heart" of the new microphone, which ranksahead of all other types for sound amplification, is ametal ribbon only a quarter of a thousandth of an inchthick.

Ardente will also display more than twenty variedexamples of their amplifier units, the majority of whichwill be housed in black ripple cases with chromefittings, together with loudspeakers, microphones, etc.

DE LA RUE & CO., LTD, T., 90, Shern Hall Street,E.17. Stand No. 6.

THIS exhibit, being of a Trade nature, will consistof moulded atticles designed especially for

manufacturers, and will form a very interesting display.

DEW, A. J. & CO., LTD., 33, Rathbone Place, W.1.Stand No. TS.

DIBBEN, HORACE, LTD.,34, Carlton Crescent,Southampton. Stand T.1THIS exhibit is of a wholesale type, featuring

commercial receivers of well-known makes.

.DIGGLE & CO., Jane Street, Rochdale. Stand No. 15.

DUBILIER CONDENSER CO. (1935), LTD., DuconWorks, Victoria Road, North Acton, W.3. StandNo. 39.

AMONG the many interesting condensers and otheraccessories to be seen on this stand will be two

new types of moulded mica condenser. These aremoulded by a special process which provides perfectsealing and protection. A new range of paper con-densers with solder tag connections will also be seen,as well as non -inductive tubular paper condensers,condenser blocks, wet electrolytic condensers, dryelectrolytic condensers, and electrolytic condenserblocks and various types of resistances.

DULCETTO POLYPHON, 2 and 3, Newman Street,Oxford Street, W.1. Stand No. 119.

ALL the exhibits on this stand will consist of well-known commercial products, and it will be a

purely wholesale exhibit.

DYSON & CO., LTD., J., 5, Godwin Street, Bradford.Stand T.2.

ONLY well-known commercial receivers will beseen on this stand.

EASTICK & SONS, J. J., 118, Bunhill Row, E.C.1.Stand T.24.

EAST LONDON RUBBER CO., LTD., 29/33, Gt.Eastern Street, E.C.2. Stand No. T9.

AGAIN, as wholesalers, the products on this standwill consist entirely of well-known lines and no

products of the East London Rubber Co. will be shown.

EAVESTAFF CO., LTD., Autoplayer Factory, AshfieldRoad, N.4. Stand 225.

ECONASIGN, CO., LTD., 92, Victoria Street, S.W.1.Stand 222.

EDISON SWANELECTRIC CO.,L T D., 1 5 5,Charing CrossRoad, W.C.2.Stand No. 42.

ik COMPLETEI -A range ofMazda valves willbe featured " onthis stand, andthis will be aug.mented by adisplay of cathoderay tubes andspecial valves, andthe B.T.H. pick-ups and similar ac-cessories., Hi addi-tion thefull rangeof Ediswan Ex.tra Life Accumu-lators and theTungar RadioBattery Chargerswill be seen. Inconnection withthe latter somenew models will be

A new FidelityRibbon -Type Micro-phone developed forP. A. work by

Grampian.

seen for the first time and these include models suitablefor home use as well as for those operating largebattery charging stations. The latest B.T.H. pick-upis the Minor model, which now costs only 17s. (K.I.complete with self-contained volume control.

EFFICIENCY MAGAZINE, 87, Regent Street, W.1.Stand 221.

ENSIGN LTD., 88, High Holborn, W.C.1. Stand T.22.ONLY exhibits of a wholesale nature will be shown

here.,

EPOCH REPRODUCERS, LTD., Aldwych House,Aldwych, London, W.C.2. Stand No. 94.ANEW super -'cinema loud speaker will be shown on

this stand; and existing models such as theDomino Model 1011 and DI speakers will be seen inimproved designs. A new suspension material is nowbeing employed -on-the -outside edge of the cone andthis has increased the frequency response of themodels. A P.M. super-einema model Is also beingintroduced and is capable of handling 30 watts ofundistorted speech. A new range of horns for usewith speaker units and an improved microphone willalso be seen.

EVER -READY CO. (Gt. Britain), LTD., Hercules Place,Holloway, N.7. Stand No. 58.

TN addition to a full range of batteries of all types,I The Ever -Ready Company will also be exhibiting

a complete range of receivers, including portables,transportables and table model superhets.

One of theGrampian P. A.

Loudspeakers.

EVERETT, EDGCUMBE & CO., LTG., ColindaleWorks, Hendon, NAVA. Stand No. 213

THE complete range of meters and test equipmentto be seen on this stand includes some useful

equipment for the experimenter as well as for theservice engineer. An .all-purpose tester, a visual valvetester, and a service valve tester have all been improvedthis year, and the illustrations on this page show thefirst two of these exhibits.

FARREX RADIO, Rear of 643, Holloway Road,London, N.111. 7 Stand No 218;

THE range of apparatus to be seen on this standwill include All -Metal Converters, a Universal

Power Pack, a Dual -Mick Converter, Public AddressEquipment and Power Units. The public addressequipment will embrace microphones, projectionspeakers and amplifiers, and certain models havebeen developed to render them suitable for televisionpurposes.

August 29th, 1936

The latest Fidelity Auditorium Type GoodmanSpeaker.

FERRANTI, LTD., Radio Works, Moston, Manchester10. Stand Nos. 8, 83, 216.

THE main Ferranti stand will be utilised solely forthe purpose of showing the new all -wave range

of receivers, radiograms, and extension speakers.The receivers include various all -wave models, andan interesting feature is the ingenious tuning scalewhich is incorporated to simplify tuning on the shortwaves. A separate small stand will be devoted to thedisplay of a very comprehensive range of 2hin. movingcoil, A.C. rectifier electrostatic and thermal instru-ments, whilst in addition a variety of components,ncluding transformers, chokes, condensers, resistances,speakers and similar items will be on view.

FILM INDUSTRIES LTD., 60, Paddington Street, W.1.Stand No. 4

PUBLIC Address apparatus NA ill form the bulk ofthis exhibit, and the apparatus displayed will

include loud -speakers of boils the cone and the horntype. -Microphones, amplifiers and special school radioequipment will be seen, the latter taking the form of aneat portable equipment mounted on castors, anddesigned- to deliver sufficient power to supply up toeight extension loud -speakers. The small " Baby "P.A. equipment employs a battery -operated amplifierwith a Class B output stage and will no doubt proveof considerable interest as it feeds a 4Oin. all -metalhorn -type loud -speaker.

Two interesting items horn theEverett Edgctimbe range of testtnstruments-A Valve -Tesler

and All -Purpose Tester.

August 29th, 1936 629PRACTICAL AND AMATEUR WIRELESS

NATIONAL.R.A010

EXHIBITION

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FLINDERS (WHOLESALE), LTD., 14-20, St Peter'sStreet, Ipswich, Stand 1.16.

THIS exhibit, also, is of a wholesale type.

FULLER ACCUMULATOR CO. (1926), LTD., Wood-land Works, Chadwell Heath, Essex. Stand No. 101.

ANEW accumulator, type FM0 (illustrated on thispage) will be an attraction on the Fuller stand

and will take its place amongst the vast range of Sparta

T he Magnascopic dial on the Ferranti rsceiv:rs ischatty seen in this illustration.

SHEL-11,reSTO 8, FROM

OLYMPIABV UNDERGROUND &

MOTOR BUS.

UnclergrOund RakuayS.MorOr eusRo,res

-BUSES PASSINGOLYMPIA Nos.

'The new FMC model Fuller accumulator.

dry batteries and other multi -plate accumulators.'the range of H.T. dry batteries has been considerablyextended and it is now possible to select a battery forpractically every commercial receiver which is manu-factured.

GARRARD ENGINEERING & MFG. CO., LTD.,.Swindon. Wilts. Stand No. 37.

IN addition to the already popular range of gramo-phone accessories of Garrard make, a new

Automatic Record -changer will be seen this year.This includes a pick-up and arm and is supplied com-pletely ready tbr fitting in position in the cabinet.Phis changer will play automatically and consecutively

eight 10in, or eight 12in. records of any make providedthey have the central run-off or eccentric groove.When the last record has been played the changerautomatically stops and switches off the electriccurrent. A rejector control is fitted.

GENERAL ELECTRIC COMPANY, LTD., MagnetW.C.Y.

STAND No. 51 will attract attention by the artisticlines of its layout and the original lighting effects

which form part of it. The display has been designedto give leisurely inspection of the complete range ofreceivers ranging from a simple battery 3 -valuerutilising a straight circuit to an all -wave record -changing radiogram. On Stand No. 40 displays ofvalves and public address and relay equipment willbe given, one of the most interesting items being apiece of apparatus illustrating the functioning of thecathode-ray tube. Another working model which willattract attention is that illustrating clearly the effectof overloading various types of power valve.

Ctrs, Radio 11,41 be showing this Portadyne receiver.

1937 STENTORIANSEE THEM AT RADIOLYMPIA

STAND 66


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August 29th, 1936

&AMATEURAitg,110A WiRELEs '" ,E.y.- ., . ,.

,.. .., ....._._..... _. ..

GILBERT & CO., C., 73, Arundel Street, Sheffield.Stand T14.

GOODMANS INDUSTRIES, LTD., Lancelot Road,Wembley, Middlesex. Stand No. 87.

AHONG the loud -speakers to be exhibited on thisstand will. be, the 12in. auditorium high-fidelity

speaker which is illustrated on page 628. An entirelynew model, a 10in. auditorium model designed for a

The New Garrard Auto -recordUnit.

power output (6 watts) will also be seen, and amongthe remaining models is an Sin. chassis model, con-tinued from last year,

is.the 24B semi -projector

model with a 241n. flare. This model is fitted with anentirely new unit, and still cOsts'El0. The new modelAirfio extension walnut cabinet loud -speaker, completewith volume control, will also be seen.

GORST ELECTRICAL CO., LTD., Portadyne Works,Gorst Road, North Acton, London, N.W.10.Stand No. 46.

THE complete range of Portadyne receivers will beseen here, and these will include Model A.64,

shown on page 629. This is a 0.-valyeistiperhet coveringfour wave -bands (including the short waves from 16 to50 and from 50 to 150 metres). An important featureof these receivers is the inclusion of the " Porta "aerial and tone control.

GRAMOPHONE CO., LTD., 98, Clerkenwell Road,E.C.1. Stand No. 54.

THIS exhibit consists of seventeen receivers andradiograms. and two new Television receiving

instruments. One of the latter is illustrated on thispage and will no doubt attract considerable attentionin view of the forthcoming transmissions. Thereare two television receivers, one of which has afixed -tuned sound section to simplify operation,and the other has 6, standard radio section. AnImportant point regarding the standard radioreceivers is that in some of the all -wave modelsthe lower wavelength covered has been reducedto 7 metres so that the sound portion of thetelevision transmissions may be heard. Thenovel cabinet designs will also prove interestingand some radical changes from orthodox practicewill be seen and will no doubt form the topicof considerable discussion among the visitors to theexhibition.

GRAMPIAN REPRODUCERS, LTD., Kew Gardens,Surrey. Stand No. 21.

THE majority of the apparatus on this stand willconsist of public address equipment and this will

embrace microphones, loud -speakers and amplifiers.

hoicks Radio are showing an ordinary Battery Three inaddition t o some elaborate special sets.

For big outdoor events, the model 25 amplifier, de-livering a 25 watt undistorted output, will attractattention, and is stated to have a frequency characteris-tic which is linear within 3 db. up to 10,000 cycles.Other items include the moving -coil microphone andprojection speaker designed to handle 12 a atts.

HACKER & SONS, H. Perfecta Works, Ray Lea Road,Maidenhead. Stand No. 29.MESSRS. HACKER will be showing a range of

high-fidelity radio-uramophoneS and receiversander the name of Dynatron. This year there will be

four completely stew models, the Victor, VikingValkyrie, and Vulcan. The Ether Empress is anall -wave if valve automatic radiouram, a com-plete high-fidelity instrument for the music lover.

HARMER & SIMMONS, LTD.,Electra House, 223, Hoe Street,Walthamstow, E.17. Stand No. 217.

THE apparatus shown here willconsist of special output

rectifiers for use with all types of apparatus requiringdirect current. In addition there will be othermains equipment including .rectifiers, eliminators,and gas -filled valve rectifiers ,for ,use on a 400 volt3 -phase supply for battery charging.

HARRIES THERMIONICS, LTD., Avenue Chambers,Vernon Place, W.C.1. Stand No. 2.

HAYNES RADIO, LTD., Queensway, Enfield, Middlesex.Stand No. 13.AS in previous years, the exhibits on this stand will

consist. of high -quality receivers and radio-grams. Muse interesting amplifiers will also be shown,and these include the Duophase method of L.F.coupling invented by Mr. F. H. Haynes. The receiverswill attract attention on 'account of the fact that thevisual tuning indicator which is fitted consists of astandard milliammeter, in Contrast to the variousingenious " thermometers " and other devices whichare used on other receivers. The Haynes Loud -speaker,a heavily -built quality Component, \ t also beshowm.

HEAYBERD & CO., F. C. 10, Finsbury Street, London,E.C.2. Stand No. 25.

THE major portion of this exhibit will consist ofmains accessories, Rich aS transformers, chokes,

etc. In addition to these, some complete mains unitswill be seen in company with various chargers, bothfor the amateur and for the service engineer. This

Simpson's 'Synchronous Turntable will again be featured :onStand No. 88.

year a new amplifier of the portable type will be onshow, and will attract attention in view of its noveldesign and low price.

HENDERSON'S WHOLESALE ELECTRICAL &RADIO LTD., Electric House, Queen's Road, Brighton.Stand T17.

HENLEY'S TELEGRAPH WORKS CO., LTD., HolbornViaduct, London, W.C.1. Stand No. 28.

THIS stand will be devoted almost exclusively tothe Solon electric soldering iron, which is now

one of the most popular irons amongst home construc-tors. In addition, many manufacturers employ thelarger model of the. Solon iron, which is availablewith a 240 -watt dissipation. A new pencil -pointAnt will be seen this year and will prove veryuseful for making connections in the latest typesof small and compact receivers.

HIGH VACUUM VALVE CO.' LTD., 113,Farringdon Road, E.C.1. Stand No. 26.

A MOST interesting range of valves will formthe main portion of this exhibit and the

midgets will no doubt attract the greatest amountof attention in view of the present popularity ofthe midget type of receiver. The special valvesfor short-wave use and other specialities will alsomake this an attractive exhibit.

1111

One of the first Television receivers to be produced forOlympia-This is an H.M.V. model.

£6 5s. (C.W.37) to a 22 -guinea all -wave mainsradiogram. The range includes a special Fisher-man's, set which is a three -waveband receiverdesigned especially to withstand the effects of seaspray and other climatic extremes met with in ayacht or fishing vessel. Theeabinet is of Bermudateak and the cost is £9 19s. 6d.

ISMAY DISTRIBUTORS, LTD., Sterling Works,Dagenham. Stand 73.

JACKSON BROS. (LONDON), LTD., 72, St. Thomas'Street, London, S.E.1. Stand No. 81.

THE main part of this exhibit will consist of variablecondensers and drives, and tissue extend Irons a

simple single short-wave unit to ganged units of fourseparate sections designed for use in commercialsuperhero. The range of drives will prove especiallyattractive and these may now be obtained with wave-length calibrations designed for use with modern coils.Control knobs and similar smaller items will also beseen. together with some special complete tuners inwhich the coils are also included.

HILLMAN BROS., ;LTD., [123, Albion Street, Two of the new Solon Electric Soldering Irons, showing theLeeds, Stand T3. new Pencil -point bit.

HOBDAY BROS., LTD., 21, Gt. Eastern Street,E.C.2. Stand T20.

Tilts is a wholesale exhibit.

INVICTA RADIO, LTD., Parkhurst Road, London, N.7.Stand No. 35. -APOPULAR range of receivers will be seen here,

ranging from a three -valve battery model at

-Win a W.B. Speaker!Turn -to page 606.


KINGSWAY ELECTRICALS, LTD., 3 to 9, Dane Street,London, W.C.1. Stand No. 88.

THE Simpson electric turntable is the main featurehere, and in addition a number of component

parts manufactured to special orders will also he seen.It will give some idea of the wide range of componentswhich can be made by this particular firm.

The Airplane Type die/ is featured in the Listen setshown above.

KOLSTER-BRANDES, LTD., Cray Works, Sidcup,Kent. Stand No. 57.

AMONG -the-many receivers to be shown en thisstand the principal new features to he ineluiled

are known as the " Supermagnidyne " device. whichis the name given to receivers incorporating specialtuning coils wound with multi -strand Litz wire: the"Fototune" tuning dial; the '" K -Beacon " ,t wyde-ray. visual tuning indicator ; the differential tonecontrol. In addition, of Course, the well-knownRejector:dal feature will be prominently displayed.

LECTROLINX, LTD., 79a, Rochester Row, London,S.W.1. Stand No. 82.

THE home -con d rie-tor will find this stand- ofparticular interest in view of the many small

components which will be featured. These includevalveholders, connector strips, plugs, sockets, andsimilar items. New items this year will be the fuseplugs, a loud -speaker control panel with ".ping -switch," and the skeleton valve adaptor.

L.E.S. DISTRIBUTORS, LTD., 15, Alfred Place, Totten-ham Court Road, W.C.1. Stand T21, T26.

LINGUAPHONE, LTD., 24-27, High Holborn, London,W.C.1. Stand Nb. 106.

FOUR radio -grams will be seen here, the sin:Westa recording gramophone which, although little

larger than a portable set, has an Sim internal energisedmoving -coil speaker. The largest model is an " All

World " recordiogram costing 50 gns. and employing8 valves with a push-pull output stage feeding aduode speaker. This set covers four separate wave-bands and full provision is Made for making gramo-phone records.

LISSEN, LTD., Worple Road, Isleworth, Mddx. StandNo. 64.

A N extensive range of receivers, batteries, and valvesA will be seen on this stand, and the portablewith the novel loud -speaker mounting will no doubtprove the most interesting in view of the departurefrom normal design. This particular receiver isillustrated on page 642 and the method adopted mayclearly be seen.

LONDON ELECTRIC APPLIANCES, LTD., 62, GlengallRoad, Old Kent Road, S.E.15. Stand No. 212.

AMONG the receivers to be shown here are theJunior, Senior, Major, and the Grand. These

are all 4 -valve portables, and the Major is fitted withdetachable handle and turntable. These receivers allincorporate the Hivac midget valves and a furthernovelty fitted in the Grand is a battery economisercircuit.

LUGTON & CO., LTD., 203, Old Street, London,E.C.1. Stand No. T5.

ALTHOUGH the main portion of this exhibitwill be of a wholesale nature, representative

of all the well-known models,the Maxitone accumulators andother spcialities of Messrs.Lugton will be 011 view.MANUFACTURERS ACCE 8-

SORIES CO. (19281, LTD.,85, Gt. Eastern Street, E.C.2.Stand No. 17:

fi I S exhibit will also be of a wholesale nature,1 featuring well-known receivers for which Manu-

facturers Accessories are acting as distributors.

Marconiphone Swill also be showing a Television receiverand this illustration shows how the screen has been mounted

Just a few of the many specialised components produced by Kingsway Electricals.

631

MARCONIPHONE CO., LTD., Tottenham Court Road,London, W.C.1. Stand No. 49.

AMONG the many new receivers to be seen herethe Television receiver will undoubtedly create

the greatest interest. Other important features which

An extremely efficient Portable-The Wayfarer " Grand"'produced by London Electric Appliances, Ltd.

will identify the Marconiphone sets are the specialmaterial used for the loud -speaker opening, the novelmanner in which the latter has been developed, and theunusual cabinet designs. The new tuning indicatorswill also strike a navel note, and the special giantdisplay models will give the stand an attractiveappearance.

One of the LinguaPhcne Recording Radiograms

"CONSTRUCTORS OWE YOUA DEBT OF GRATITUDE"

Says Mn F. J. Camm


MeMICHAEL RADIO, LTD., 205, Strand, London,W.C.2. Stand No. 47..

-j'EN new models will be on view on this stand,and the makers claim that this will be the most

comprehensive programme which they have everoffered to the public. The receivers include six mainsand four battery models and the novel tuning dialwhich has been included in Model 366, actually mountedand recessed into the underside of the cabinet lid,will prove a great attraction and greatly simplifiestuning.

Tuning in sim-plified in thisMc Michaelre-ceiver owing totheGrant TuningDial which isfitted inside thelid and which isoperated bs thenormal .controls.

MILMES RADIO CO., LTD., Church Street, Bingley,Yorks. Stand No. 205.

THE H.T. Supply Unit will continue to be the mostprominent feature on this stand, and the design and

price remains nnchanged. Two new lines to be seenfor the first time will be the SP. 60 Charging Batteryand ST switch. The former is a 0 -volt L.T. accumu-lator with plates of the car starter type, and each cell isprovided with separate screw terminals instead of the

customary lain -bars. The switch is designed to screwat the end of the mains unit and enables the three cellsto be connected in series or parallel for charging andvalve supply purposes.

MULLARD RADIO VALVE CO., LTD., Mallard House,Charing Cross Road, W.C.2. Stand No. 62.

AL T110 UGH valves will form a large proportion of theexhibits on this stand, the new receivers will prob-

For P.A. work thisPrism Loud Speakergives surprising re -

sails.

For the deaf or hard of hearing this Multitone device enables the programmes to be heardwithout inconveniencing others.

ably prove jest as attractiveto visitors to the show. Thenovel cabinet designs whichhave been introduced, coupledwith the new control featuressuch as the " Uni-knob," willattract many, and as usual thegiant models of various itemswill initiate the newcomer intothe mysteries of many of theusual radio accessories.

MULTITONE ELECTRIC CO.,LTD., 95-98, White LionStreet, Islington. StandNo. 86.THE main feature on this

stand will be the Adaphonedevice, designed to enable adeaf person to join the restof the family circle inhearing the broadcast pro-gramme from the standardbroadcast receiver. Thelistener cannot be jarred orstartled by a sudden loudaccess of sound, whethercaused by someone else turningup the volume control or bya loud burst of music, owingto a special method of auto-matic volume check includedin the device. A manifoldsystem of insulation also avoidsthe danger of shock either ona battery or a mains set.

A cabinet with distinctive lines used for one of the new Mallard ail -wave -reeeioers.

A quality radiogram withmany novel features. Thisis a Prism Product with s,

specie! speaker.

NEW LONDON ELEC-TRON WORKS, LTD.,East Ham, London,E.6. Stand No. 22.

A'HONG the manynovel radio acces-

sories to be seen herethe new Screened Su-perlal and the all -waveaerial -101 be the mainfeatures. In addition the(Hobe aerial will also beprominently displayed.together with varioustypes of aerial wire.

nil, . 00

GEORGE NEWNES, LTD., Sill, Southamp-ton Street, Strand, London, W.C.2. StandNo. 10, Ground Floor.

MESSRS. GEORGE NEWNES, Ltd., prob-ably publish more technical :wireless

handbooks, blueprints, and wireless and tele-vision periodicals than any other publisher.On this stand, therefore, you are bound tofind a book or a periodical which appealsto you.

PRACTICAL AND AMATEUR WIRELESS,Practical Mechanics, Practical Motorist,and The Cyclist are but a few of the leadingjournals on show here. A full range of blue-prints of wireless receivers ranging fromcrystal sets to multi -valve superhets will beon sale, as well as a full range of technicalbooks, including " The Wireless Con-structor's Encyclopaedia," " Everyman'sWireless Book," " Television and Short -Wave Handbook,"" The Practical Motorist'sEncyclopedia," "The Home Mechanic'sEncyclopaedia," "Ralph Stranger's WirelessLibrary." You will also be able to inspectMr. Carom's series of receivers and thereceivers described in PRACTICAL AND

I AMATEUR WIRELESS during the past year.Mr. P. J. Carom and the technical staff

I will be available to answer readers' queries; free of charge. Call and see us.


PARTRIDGE WILSON & CO., Davenset Works,Evington Valley Road, Leicester. Stand No. 107.

MNY of the well-known Davenset Battery Chargerswill be seen here, together with some specialmodels

designed for the charging of H.T. accumulators. Inaddition a full range of battery charging accessories,

Two of the T.C.0 electro-lytic condensers.

such as cell -testing voltmeters, non -corrosive batterycliPs,.hydroMeters, etc., will also be shown.PHILIPS- LAMPS, LTD., 145, Charing Cross Road,

W.C.2. Stand No. 43.MNY novel features are to be seen on this year's

Philipareceivers, and the single -knob control whichenables tuning, volume, tone,'selectivity and so on to becarried out by means of a single control, together withthe affjustable tuning scale will prove of the greatestinterest. The scale may be raised or lowered to providethe most easily -read position, yet the pointer, as well asthe visual tuning indicator and the wave -range switchIndicator work perfectly in all positions.PLESSEY COMPANY, LTD., Vicarage Lane, liford,

Essex. Stand No. 27.THE exhibits on this stand will consist of components,

chassis, etc., made up especially for set manufac-turers, and will furnish an interesting illustratibn of themethods involved in modern set construction.

I PRACTICAL & AMATEURWIRELESS

: See George Newnes, Ltd., p. 632

PRIMOGRAPHIC, LTD., 40-44, Chipstone Street,W.C. Stand 223.

RIMUS MFG., CO., LTD., Primus House, WillowStreet, E.C.2. Stand 1A.

PRISM MFG. CO., LTD., California Works, BrightonRoad, Belmont, Surrey. Stand No. 80.

HIGH -quality reproduction has been achieved in thePrism radiogram by the use of an ingenious type

of built-up loudspeaker and the cabinet is open on allsides. In addition to this speciality, some interestingpublic-address equipment will also be exhibited.PTE RADIO LTD., Africa House, Kingsway, London,

W.C.2. Stand No. 48.PFTEEN new receivers will be on view on this stand.

and the models will cover practically all require-ments. An interesting feature of the new receivers is thatmany parts which are Incorporated are immediatelydetachable and Interchangeable. Two models are beingkept secret and will not be despatched from the

The new season's Ultra models have many newfeatures. Above is the Model 48. in a novel

cabinet design.

Cambridge works of the company until the morning ofthe exhibition, when they will be flown to Londonby autogyro. All -wave tuning Is animportant feature ofthe new sets, the short waveband being covered intwo separate stages.

RADIO GRAMOPHONE DEVELOPMENT CO., LTD.,18-20, Frederick Street, Birmingham. Stand No. 58.

FOUR 6 -valve receivers, an 8 -valve and a 12 -valveradiogram will be the main items on this stand.

All these models are of the " all -wave " type,, with fourseparate wavebands. The larger models incorporatesuch details as " mystic ray " tuning, 5 -point high andlow -note balance control, automatic record changing,

A quality receiver in a table console cabinet.One of the 1937 R.G.D. models.

J

Shaftesbury Microphones' latest mode/-The Bio-Tran.

etc. In addition, the largestmodel incorporates a newfeature known as a contrastcontrol valve which gives thecorrect relationship betweenthe loud and quiet passagesin reproduction.

RADIOMETERS, LTD., Dun-bar Works, Dunbar Street,West Norwood, S.E.2T.Stand No. 203.

AMONG the various measur-ing instruments to be

seen on this stand is theresistance and ca pacitymeasuring bridge, the valveanalyser, an A.C. voltmeter,an adaptor for the all -wavetester, and a universal meterfor measuring D.C., volts,current, and ohms.

633

RADIO RESISTOR CO., LTD., 1, Golden Square, WA.Stand No. 16.

RESISTORS of all types will be shown on this stand,and these are available in every conceivable

ohmic value from 1 to 40 megohms in 1, 2, and 3 -watt

Ultra's' latest model, 99,

ratings at ls. per watt. In addition, grid leaks Invarious values with wire ends, insulated resistors ofthe miniature type in ,i-and 1 -watt ratings, kits of

wire-wound resistance and volume controls.will be featured. In addition, suppressors for use with -car radio apparatus will also be seen.

RADIO SOCIETY OF GT. BRITAIN, 53, VictoriaStreet, S.W.1. Stand 214.

RAWLPLUG CO.' LTD., Rawlplug House, CromwellRoad, S.W.7. Stand No. 79.

THE main items on this stand Mil be Rawlplugs,plastic wood, and the special heat -proof adhesive

Duroflx. The latter is of great value to the homeconstructor for the mirth* and manufacture of loud-'speaker cones, etc. Plastic wood also is of value- forthe repair of cabinets and similar processes.

REPRODUCERS & AMPLIFIERS, LTD., FrederickStreat, Wolverhampton. Stand NI. 92.

THIS display will consist of high-grade energisedand P.M. types of loudspeaker. Special models,

not offered for sale direct to the public, will be avail-able for inspection by designers and constructionalengineers. Other apparatus to be seen will consistof P.A. sound -projection equipment featuring ex-ponential horns and a new P.A. unit with a 101in.chassis.

RIST'S WIRES & CABLES, LTD., Waveney Works,Lowestoft. Stand No. 208.

THE display here will consist of various types ofwire from lead-in cable to headphone leads. The

range includes special aerial wires, loudspeaker cords,multiway cables, slip -back connecting wire, andscreened tubing.

Tonnoy, the sound people, make a speciality of P.A. equipment. One is seen above.

I e i et

1 it ,,,,i

V


ROTHERMEL, R. A., LTD.,Rothermel House, Canter-bury Road, N.W.6. StandNo. 89.TIl E " Radio -heart " will be

the most interestingfeature on the Rothermelstand, and this consists of acomplete chassis covering fourwavebands (from 16.5 to 2,400metres), complete with tuningcondenser, coils, etc., andonly ' needs the necessaryvalves to be plugged into theholders mounted on it inorder to convert it into acomplete " receiver." Theunit is complete with dial.In addition to this there willbe the usual range of piezo-electric components, such aspick-ups, tweeters, andmicrophones.

SELECTA GRAMOPHONESLTD., 81, Southwark Street,S.E.1. Stand T11.

SELF -CHANGING GRAMOPHONES, LTD.,11, Berkeley Square, W.1. Stand No. 59.

THE main feature of the apparatusshown on this stand will be the special

seif-changing record mechanism. The specialcabinet designed by Robert Butyens,shown on another page in this issue, willbe a prominent feature, and, the portable automaticradiogram will also attract attention. Finally, therewill be a special remote control systein which allowsfor the operation of the automatic gramophone froma number of different points in a house, with extensionspeakers for the purpose.

SHAFTESBURY MICROPHONES, LTD., 24, AldersgateStreet, London, E.C.1. Stand No. 99.

THE Bio-Tran microphone, the ;Junior Microphone,and special power amplifiers will be shown here,

together with a complete range of box and exponentialborn type speakers capable of handling up to 20 watts.

SIEMENS ELECTRIC LAMPS & SUPPLIES, LTD.,38-39, -Upper-Thames Street, E.C.4. Stand No. 60.THIS exhibit will comprise a comprehensive range of

Full O'Power batteries, amongst which will befound a type suitable for practically every receiver on.the market. In addition, a range of small batteriessuitable for torches and lamps will be featured,

August 29th, 1936

Two new Varleg Coil Unitsand a new I.F. Transformer.

Above is seen one of the new Vidor receivers,and on the right and left are two WharfedalecomPonents, the left-hand model being a small

loudspeaker designed to be held in the hand.

SOUND SALES, LTD., Marlborough Road, UpperHolloway, N.19. Stand No. 78.

INCLUDED in this exhibit will be amplifiers.speakers, chargers, microphones, and a complete

Quality Radiogram. This particular model will befitted with a gramophone record -changer and a 4-12watt quality amplifier, feeding a super auditoriumspeaker.

STRATTON & CO., LTD., Eddystone Works,Bromsgrove Street, Birmingham, 5. StandNo. 23.

ALL of the apparatus shown on this standwill be designed for short-wave work,

and will include a new 8 -valve batterysuperhet, built for tropical use and fitted withall up-to-date refinements, such as A.V.C.and push-pull output stage.' Some new short-

wave coils of the interchangeabletype will also be seen in companywith many existing popular short-wave items.

TANNOY PRODUCTS, CanterburyGrove, West Norwood, S.E.27.Stand No. 45.

ALL of 'the apparatus on view herehas been designed for public-

address work, and includes amplifiers,speakers: and microphones.Every branch of the subjectis covered by these items,and the makers have a wideexperience in the subject.

TELEGRAPH CONDENSERCO., LTD., Wales FarmRoad, North Acton, W.3.Stand No. 68.TTill:T.C.C. exhibits will

consist of all types ofmica and paper fixed con-densrers, including non -inductive paper tuhulars, andspecial components for car

radio work. In addition, dry and wet electrolytics will beseen and a special feature will he the surge proofvoltage regulating wet electrolytics designed for usein A.C.J.D.C. receivers. All types of moulded con-densers and transmitting and high -voltage condenserswill also be seen.

For the Books,Blueprints, Periodicals,and Reader Service,visit our Stand, No. 10,

Ground Floor !

1937 STENTORIANNOW--

A NEW AND HIGHER STANDARD OF REPRODUCTION


FOR EVERYTHINGTHAT YOU SEE ATPETO-SCOTT OLYMPIA

ESTpao_Xcow NOISE -SUPPRESSING - IMMEDIATE DELIVERY of all latest Speakers, Eliminators, Kits, Pick-ups, Testing Meters.Receivers for CASH, C.O.D. or Easyway. Quotations of anything Radio on Request. PILOT

ALL -WAVE AERIAL 1919 Eliminates Man -Made Static.

AsSNIBLEDani READY

FOR and 7 monthlyERECTION payments 1 28.

Increases Signal Strength on all inimibands.

Improves Selectivity. MEW Waterproof and Weatherproof.Obtain the utmost entertainment fromyour radio set by using this Peto-Scott Aerial Outfit, the first reallyeconomical solution for overcomingthe noise of man-made static.AERIAL OUTFIT COMPRISES

Duplex enamelled strandedaerials, 4 insulators, 50 feetwaterproof "lead-in" wire,Aerial and Set Transformers,all assembled and readywith detailed Instructionsand drawing illustratingthe method of erection.

Cash or C.O.D., Carriageraid. 17 e.

Pao -Scot& 1937 ALL -WAVES.C.3 KIT

ana 11 monthly

World wide programmes onall wave - lengths, 16 - 2,100metres. Every constructorshould build his OVTLI all -wave set and enjoy the thrillof All - Wave listening thatwill bring programmes fromall over the World. Pete -Scott offer you a Kit whichis, in the words of a famousdesigner, " An 'amazingly eft'.cleat, yet simple to buildKit set."

NO COIL CHANGING. LOW LOSSROTARY SWITCH. PRESSED STEELDRILLED CHASSIS. S.G., DETECTORand PENTODE CIRCUIT. ("FULL INSTRUC-

payments of7/- TIONS AND DIAGRAMS.

Carriage Paid : :KIT "A " Gash or C.O.D: 17 6Complete Kit of components, less valves and cabinet.11. WNW 111,111 RIM '111101/ MOM

I KIT " B " As for Kit " A " but with 3 recom-mended Hivac valves. Cash or C.O.D. Carriage

I Paid. £5 : 0 : 3 or 9/- deposit and 11 monthlypayments of 9/3.

CONNECT THIS Pao -,StorZSHORTWAVE AC/DC PRESELECTOR

TO YOUR EXISTING SET

Absolutely Readyfor Use.

O Dual Ratio flow -Motion Dial (8-1,100-1)

IV Wavelength -Calibra-ted Scale.

B.V.A. Valves.

and tune into America and thewhole World on Short Waves.Only a few simple connectionsnecessary and NO ALTERA-TIONS to your receiver. Incor-porates special coil unit covering13 to 74 metres and is equippedwith an arrangement whereby justa turn of the switch by-passes thePre -Selector so that your set Isthen available for reception onnormal broadcast wave -lengths.Suitable for all receivers, A.C.,D.C. or batters/. Providing maims

supply is avail-able.

and 11 monthlypayments of 9/-.

COMPLETEwith valves andcabinet illustrated

14 : 17 : 6Cash or C.O.D.Carriage Paid.

13.T.S. SUPERHET CONVERTER13-71 Metres. on Your Present Set I KIT

No Coil Changing.Ready drilled andEnamelled Steel Chassis.

Simple to Build.This amazingly sensitiveSuperhet Converter Kitset ON EASY TERMS.Build it in an eveningand connect it to yourexisting set. Equippedwith self - contained dualrange coil and rotary

switch (13-29 and 30-71 metres).Suitable for an, Battery receiver.

COMPLETE K I Tand 9 monthly comprising all ;noes-payniqnts of 4/-. eary parts with full

instructions and 'dia-grams, less valves.Cash, C.O.D., Car-riage Paid, £1 :17:6

2 B.V.A.Valves 18/8estra

Fully described in No. 2 B.T.S.SHORT WAVE CONSTRUCTOR.

Post Free Cid.

AUTHOR KITS are guaranteed to specification, build one and be satisfied.

The following comprises just a small selectionof 1937 productions that we can simply for INN.CASH, C.O.D. or EASYWAY. Many moreavailable. SEND POE QUOTATION. 1011W

NEW SPEAKERSBLUED SPOT SENIOR SPEAKER; complete with Send

multi -ratio transformer which provides 16matchings, and 4 low impedance tappings forExtension Speaker matching. and

COLA P514 P.M.T. SPEAKER, supplied with

yCash or C.O.D..O.. Carriage Paid. 21/9/6.Balance in 10 monthly payments of 3/..

universal tapped transformer suitable forall outputs.Cash or C.O.D. Carriage Paid. 01/3/6.Balance in 10 monthly payments of 2/6.BENJAMIN "DUODE 33" SPEAKER. Double

voice coil construction and provided withHum Neutralising Coil and tapped transformer.Cash or C.O.D. Carriage Paid. 115/5/0.Balance in 11 monthly payments of 9/9.CELESTION 71771/OR S SPEAKER. Permanent Send

Magnet speaker with matching transformersuitable for all outputs.Cash or COD. Carriage Paid. 211.5/0.Balance in 9 monthly payments of 4/-.

NEW PICK-UPSCOSMOCHORD MODEL 10. Pick-up head only

fitted with clip for fixing to existing gramotone -arm. With silk covered connecting leads.Cash or C.O.D. Carriage Paid. 10/-.CELESTION P.2 PICK-UP. Florentine bronze

finish. Complete with volume control.Cash or C.O.D. Carriage Paid. 21/9/6.Balance in 10 monthly payments of 3/-.ROTHERMEL 88 PICK-UP. Piero -electric

pick-up and arm, with head -rest.-

Cash or C.O.D. Carriage Paid. 52/2/0.Balance in 11 monthly payments of 4/,

T.H. NEEDLE ARMATURE PICK-UP andTONE -ARM. With pick-up rest, flexible lead

and volume control. Cash or C.O.D. CarriagePaid, 22/0/0. only

Balance in 10 monthly payment' of 4/3.

NEW GRAMO-MOTORS .

COLLARO AC37 ELECTRIC INDUCTIONMOTOR. A.C. mains 100/130 or 200/200 Send

12in. turntable and fullyautomatic stop.Cash or C.O.D. Carriage Paid. 01/14/0. onlyBalance in 9 monthly payments of 4/-.COLLARD DOUBLE SPRING MOTOR, with

12in. turntable and all accessories. Willplay 2 full 12in. records at one winding.Cash or C.O.D. Carriage Paid. 21/6/0.Balance in 10 monthly payments of 2/6.

-ARRARP202A ELECTRIC INDUCTION

MOTOR. A.C. mains 100/250 volts, 25/60cycles. 12in. turntable mounted on motor platewith automatic start and stop.Cash or C.O.D. Carriage Paid. 22/10/0.Balance in 10 monthly payments of 5/-.

NEW RADIOGRAM UNITSCOLLARO AC37. RADIOGRAM UNITS.

Mounted on 8in. by 7tiu. unitplate with 121mturntable, automatic start and stop, pick-up andvolume control. A.C. mains 100/130 or 200/200volts, 50-60 cycles.Cash or C.O.D. Carriage Paid. 23/0/0. onlyBalance in 11 monthly payments of 5/6.nAIEBARD EADIOGRAM UNIT with A.C.1 Send

Electric Induction Motor. Complete withpick-up, 12in. turntable and plate. Type R.A.C. maim 100/250 volts. 50/60 cYclee.Cash or C.O.D. Carriage Paid. 28/2/6.Balance in 11 monthly payments of 5/9.

NEW ELIMINATORSDETO-SCOTT M.A. 10/30 ELIMINATOR WITH

TRICKLE CHARGER. A.C. mans .200/250volts, 50/100 cycles. Westinghouse metal rectifier.4 H.T. tappings. Output 20 m/A at 120 volts.Cash or CAD. Carriage Paid. 22/19/8. onlyBalance in 11 monthly' payments of 518.DETO-SCOTT ELIMINATOR. A.C. Send

mains 200/250,/rolts, 50/100 cycles. Incor-porates Westinghouse rectifier. 3 tappings.Output 25 m/A at 120 volts. onlyCash or C.O.D. Carriage Paid. 22/9/6.Balance in 10 monthly payments of 5/-.DEGENTONE W.I.P. ELIMINATOR with output Send

regulator. A.C. mains. 7 voltage tappings.Output 120/150 volts at 12 m/A.Cash or C.O.D. Carriage. Paid. 22/10/0. onlyBalance in 10 monthly payments of 5/-.

NEW TESTING METERSDEMO ROTAMETER. 9 ranges, 100 testa. Send

Mains or battery receivers.Cash or CCD. Carriage Paid. 21/9/6.Balance in 10 monthly payments of 3/... onlyA VONINOR D.C. MAINS AND BATTERY TEST Send- METER. 10 ranges. Supplied in velvet linedcase with leads, clips and prods.Cash or C.O.D. Carriage Paid, 22/0/0. onlyBalance in 10 monthly payments of 4/8.

AVOWINOR Universal A.C./D.C. Test Meter.22 ranges. Moving Coil. 3' full scale dace -

Cash or C.O.D. Carriage Paid. 05/0/0.Balance in 11 monthly payments of 9/3.

DESCRIPTIVE LEAFLET OF ANY OFABOVE ON REQUEST.

2/6

Send

2/6only

Send

9/ -only

2/6only

Send

2/6only

Send

2/6only

rend

2/6

2/6

Send

2/6only

Send

5/ -only

Send

5/-

5/ -only

Pend

5/-

5/-

5/-

2/6

2/6

9/ -only

, LOT.AUTHORAny item supplied separately. Orders over 10/ -

sent C.O.D.-carriage and post free.

BANDSPREAD S.W.3KIT SS A 99 CASH OR C.O.D. 4D 3: 5 0rs CARRIAGE PAID ose

or 12 monthly payments of 6/-.Author's Kit of first specified parts, less valves, speaker,headphones, and cabinet.With 3 specified valves. Cash or C.O.D. Carriage Paid, £4/17,0or 12 monthly payments of 8/9.

3 specified PRIMW.B. Speaker, Type 3711Pr. Ericsson headphones ..Peto-Stott Bandspread 3 cabinet

s. it... 1 12 0.. 17 6

15 019 6

GLADIATOR THREEKIT si A 99 CASH OR C.O.D. £4:19:6

a+ CARRIAGE PAIDor 12 monthly payments of 9/-.

Author's Kit of first specified parts, less valves, speakerand cabinet.With 3 specified valves. Cash or C.O.D. Carriage Paid, £6/1,2/6or 12 monthly payments of 12/,

Pato-Scott Gladiator Cabinet.W.B. speaker, Type 37.J.3 specified Valves ..

(I.., 19 6

1 12 6.. 21 13 0

SIGNET TWOKIT ssAll CASH OR CAD.

CARRIAGE PAID £2:4:6or 5/- down and 11 monthly payments of 4/-

Author's Kit of first specified parts, less valves, cabinetand speaker.WitA specified valves. Cash or C.O.D. Carriage Paid, 02/17/9or 12 monthly payments of 5/3.

3 specified Valves ..Epoch speaker, Type S.D. ..Peto-Scott Signet Cabinel

£ s. d.. 13 3

.. 1 1 019

4g)SIENT0,101.1!OtiiN

IMMEDIATEDELIVERY 2'6W.B. 1937 STENTORIAN

JUNIOR (Type 37J) DOWN

Specified for the BandsprejdS.W.3. Incorporates the newexclusive Stentorian features andmakes an unmistakable improve-ment in volume and realism ofreproduction. Perfectly matchesany receiver as principal or extraspeaker.

CASH OR C.O.D. CARRIAGE PAID01 12 6

or 2/6 down and 11 monthlypayments of 3/-.

W.B. 1937 STENTORIAN BABY (Type 37B)Highly efficient Baby Speaker with an adaptation of the famous" Microlode " matching device. Suitable for any receiver.CASH OR C.O.D. CARRIAGE PAID .. £1 3 6

or 9/6 down and 10 monthly payments of 2/6.The undermentioned W.B. speakers, chassis and cabinet modelsare also available on attractive Easy Payment Terms. Cabinetmodels can be fitted with the new " W.B." Long Arm " RemoteControl Device at a slight increase in deposits and monthly, pay-ments.W.B. SENIOR (Type 175) SPEAKER .. 22 2 0

In cabinet with volume control 23 3 0W.B. JUNIOR in cabinet with volume contro LS 9 6W.B. BABY in cabinet .. £1 9 6

POST THIS COUPON NOWFOR THIS CONSTRUCTORS' BOOKLET -FREE

FETO-SCOTT CO., LTD., 77, CITY ROAD, LONDON, E.C.1.WEST -END : 62, HIGH HOLBORN, LONDON, W.C.LPlease send booklet describingS.W. PRESELECTOR H.T. BATTERIES

ALL WAVE S.G.3 KIT / ELIMINATORS BROADCAST S.G.3 KIT ANTI -NOISE AERIAL S.W. ADAPTOR KIT SPEAKERS TELEVISION ADAPTOR CRAMADAPTOR

NAME

ADDRESS

rr W. 18


The D.C.AVOMINOR

A compact moving -coil combination meter-t3 ranges of readingsin milliamps, volts andohms. It tests circuits,valves, components,batteries, power units,etc. Provides a de-gree of accuracy un-approached by anyother instrument atanywhere near its price.In case, with leads,interchangeable testingprods and crocodileclips, and completeinstruction book.

Price 401.Deferred Terms if desired

The UNIVERSALAVOMINOR

A smaller brother of theUniversal Avometer. Itgives 22 different ranges ofreadings (A.C. and D.C.).Has Sin. scale. Totalresistance 200,000 ohms.Complete with instructionbook, leads, and inter-changeable testing prodsand crocodile clips.

,Price £5Leather Case, 10s.

Deferred Terms if desired

The AVODAPTEREvery valve test can be made ex-ternally on the bench. No grovellingabout inside the set or having tosever connections. Tests are madewith ease and under actual workingconditions. Instantly adaptable for4 -Pin, 5 -pin, or 7 -pin valves.

Price 25/ -The AveCouPLIER

Renders the AvoDapter instantlysuitable for 9 -pin valves. Completewith instructions.

Price 12/6

" RADIO SERVICING SIMPLIFIED !!with Supplement

This invaluable book explains every phase offault -tracing and testing in non -technical lan-guage. Multitudinous tests are so set forthas to be a matter of straightforward procedure.The comprehensive information and numerousdiagrains enable everyone to test sets and apparatuswith ease and success.

Price 2/6 Post Free 2/9

August 29th, 1936

Is the performance of your set as efficient as it should be ?Nine times out of ten the reception you should get is lostbecause of small defects. If they are traced, remedied,you can put new life into the performance of that set ofyours.

With Avo ' Testing Instruments you can trace faultsspeedily and accurately. It is, of course, essential thathighly accurate instruments are used. Avo Instruments,famous for precision, are designed to meet' the needs of

every radio enthusiast as well as of service men.See Avo ' Testing Apparatus a Radiolympia.

RADIOLYMPIA

Stand 31AVO-OSCILLATOR

A compact Oscillator of ex-treme usefulness for servicework. Provides a steady localsignal, ' modulated or non -modulated at will, the funda-mental frequency of which canbe varied over the long, mediumand intermediate wave -bands.Harmonics extend the rangedown to the short waves.Small size (bins. x 4ins. x Sins.)enables the instrument to beeasily carried. Complete withshielded lead, valve and H.T.and L.T. batteries.

Price A5 :10s.Deferred Terms if desired

'AVO' TESTINGACCESSORIES

Accurate and simple testingis greatly assisted by the boxedkit of ' Avo ' Testing Acces-sories. They do away withnondescript lengths of wire.You can test more quicklywithout making dangerous mis-takes. For use with anytesting meter.

Price 2/6

TESTINGINSTRUMENTS

If you do not visit Radiolympia, write for illustrated lists of Avo' Instruments.THEAUTOMATIC COIL WINDER & ELECTRICAL EQUIPMENT CO. LTD.

- Winder House, Douglas Street, London, S.W.'. Phone: VICTORIA 3404-7.


THE 362 RADIO VALVE CO. LTD., Stoneham Road,Upper Clapton, E.5. Stand No. 207.

THOMPSON, DIAMOND & BUTCHER, 34, FarringdonRoad, E.C.1. Stand No. T4.

TUCKER EYELET CO., LTD., Cuckoo Road, Birming-ham, 7. Stand No. 105.THIS exhibit will consist of a range of eyelets,

solder tags, battery connections, and sockets,and a range of other small metal presswares for usein receiver construction. These components are, ofcourse, only employed in commercially -built receivers..

ULTRA ELECTRIC LTD., Western Avenue, Acton,W.3. Stand No. 52.THE new Ultra receivers will show many new

novelties, the most prominent of which is thenew tuning scale on Models 96 and 99. A novel typeof cabinet is also employed for Model 98, and the largeairplane type dials fitted to the remaining receiverswill prove of great interest. All -waves will also be afeature of some of the new Ultra models.

UNION RADIO CO., LTD., U. R. Works, Aurelia Road,Croydon. Stand No. 20.

VARLEY, LTD., Cambridge Place, Burrage Road,S.E.18. Stand No. 77.

SOME new components for the home -constructorwill be seen on Stand No. 77, and many existing

lines will also be seen. Among the new lines are gangedcoil units for superhet. and straight receivers and aNew I.F. transformer. Amongst the remaining linesare chokes, transformers, power resistors and thepopular thermal delay switch.

VIDOR, LTD., West Street,Erith, Kent. Stand No. 61.AMONGST the various

complete receivers to beseen on this stand willbe the miniature portablewhich has already beenreviewed by us. A short- For Television apparatus this Westinghouse rectifier will find many uses. It is rated to give an output of 650 volts.wave converter, and asuperhet. radiogram represent the other extremes, andthe new open tuning dial which is fitted to these re-ceivers will represOnt.the modern trend of tuning indi-cators.

latest product, the Voluphone, will present an entirelynew aspect- in reception conditions. This is a " handloud -speaker " designed for the partially deaf listenerIt is complete with a volume control and lalsY also beused by the ordinary listener who wishes to avoiddisturbing other people when listening to a particularitem. Extension speakers, and a moving -coil micro-phone will complete the range of exhibits.

WHITELEY ELECTRICAL RADIO CO., LTD., VictoriaStreet, Mansfield, Notts. Stand No. 66.

THE range of Stentorian speakers will again be tilefeature on this stand, and this year's models

present several interesting improvements. The latestmidget will prove popular on account of the presenttrend in miniature receivers, and the larger Seniormodels will also attract those to whom high -qualityreproduction is of the greatest importance. There is aStentorian for practically every type of receiver, andthe prices cover every class of listener. The extensionmodels incorporate a volume control so that theoutput may be regulated without the necessity forcontinual journeys to and from the actual receiver, anda new distant control, " Long Arm," is also to beprominently featured.

This year's Signior -tan has a number improvements, andthe model shown above is the Junior which may also be

obtained in a cabinet version.

WINGROVE & ROGERS, LTD., Arundel Chambers,188-189, Strand, W.C.2. Stand No. 95.

THE displays on these stands will embrace many ofthe popular Polar components such as variable

condensers, sloW-Motion drives, etc., as well as theN.S.F. volume controls, resistors, and tubular con-densers. The new condensers include the, Bar Type

two and three -gang unitsin which rigidity of (on-

' struetion has been featured,and which may be obtainedeither with bakelite or cera-mic insulation. One or twonew models have been intro-duced to replace certainmodels which were seen atthe last exhibition.

WATERHOUSE, LTD., F., Stanley Works, EdwardStreet, Dudley Hill, Bradford. Stand No. 201.

The Weston Oscillator, one of the many measuring devicesproduced by the Weston Electrical Instrument Company.

WEBBER & CO., LTD., J. M., Weblite House, 39,Gt. Eastern Street, E.C.2. Stand No. T13.

THIS exhibit will be of a wholesale nature and willembrace the various manufacturer's receivers

which Messrs. Webber are handling this season.

WESTINGHOUSE BRAKE & SIGNAL CO., LTD.,82, York Road, King's Cross, N.1. Stand No. 36.ARANGE of metal rectifiers, from the simple H.F.

type to the large charger type, will be seen here,

and amongst the new types the " H "and "J models,designed for use in modern teleVision apparatus, willbe most prominent. These are -bite high -voltage low=current types suitable for -time ,,,,base units and othercathode-ray tube circuits. Charging sets suitable forcommercial use will also be seen.

The "Long Arm" is a remote -control device produced toWIB, and gives full control over the receiver at a distant

listening Point.

WESTON ELECTRICAL INSTRUMENT CO., LTD.,Kingston By-pass, Surbiton, Surrey. Stand No. 215.

A-COMPREHENSIVE range of measuring instru-ments, including output meters, will be shown

on this stand, and some new items will include theSelective Analyzer, which is a complete testing equip-ment. Other models are the Super Oscillator, the Volt -Ohmmeter, and the Valve Voltmeter.

WHARFEDALE WIRELESS WORKS, 62, Leeds RoadBradford. Stand No. 204.

THE complete range of ..Wharfcdale speakers willform the exhibit on Stand No. 204, and the

WOODWORK, DAVIES D. AL, Trading Estate, Slough,Bucks. Stand No. 17. See also D. M. Davies Woods o rk.

An Output Meter which is another Weston product.

WRIGHT & WEAIRE,' LTD., 740, High Road,Tottenham, N.17. Stand No. 97.

THE well-known Wearite components will be showntogether with some new lines and the welcome

announceihent of a reduction in price in certainexisting models. Coils, condensers, switches, volumecontrols, mains transformers, chokes and many otherItems of great value to the home constructor will beseen, together with the range of test equipment whichwill appeal to the service engineer and the advancedexperimenter.

HEAR THE DIFFERENCE A

1937 STENTORIANWILL MAKE TO YOUR SET

638

WE have received somany inquiries foran efficient, yet

simple, two -valve receiver re-cently that it was decided toproduce a design that couldeasily be built by the veriestnovice. A chassis was chosenin preference to a flat base-board, as the finished receiveris neater and can be housed in avery small cabinet.

Circuit DetailsThe circuit is the well -tried

detector-L.F. arrangement, atriode valve being used in thedetector stage and an economypentode in the output stage.A triode could be substitutedfor the pentode, but this wouldresult in loss of volume and,therefore, the specified valveshould be adhered to. The coilis an efficient dual -range type,Wave -changing being effectedby means of an external three-point switch. It is of thetransformer type so that a' high degree ofselectivity can be obtained if the reactioncondenser is judiciously operated. This coilworks best with an outside aerial of approxi-mately 40ft. If a longer aerial is used itwill be advisable to connect a fixed con-denser of approximately .0002mfd. betweenthe aerial lead and the aerial socket of theset.

L.F. CouplerReaction is provided by means of a

differential reaction condenser, therebyensuring an effective path to earth for theH.F. component at the anode ofthe detectorvalve. A special L.F. coupling unit is used

A Simple Two-Valver forthe Beginner

between the detector and output valves.This incorporates a resistance and a con-denser as well as a transformer. Parallel--feed coupling is therefore provided withresultant good bass response. When astraight transformer coupler is used directcurrent passes through the primary windingof the transformer and bass response isconsequently adversely affected. Thetransformer section of the coupling unit hasa step-up ratio of 3-1, and, therefore, anadequate input for the pentode valve isassured.

RangeThis simple little set can be relied upon

to pick up medium -wave stations at a dis-tance of approximately 100 miles when areasonably efficient aerial is employed, andreception of Droitwich on the long wave-band may be obtained in most parts of thecountry. This does not mean that foreign


A Simple Detector -L.F. Receiver which Offers the

Utmost Simplicity of Construction and Operation, and is

Ideal for the Beginner

station reception is impossible ; with anefficient aerial several Continental stations

Full Constructional Details iwill be Given Next Week

will be picked up after dark. Full con-structional details will be given next week ;

August 29th, 1936

in the meantime, the followingabridged details will enable theconstructor to commence the

ork of building the set.

Building the ReceiverIt will be noted that the

receiver is ideal for the construc-tor who is attacking his firstpiece of constructional appara-tus, and the layout has beenarranged so that no possibledifficulty can arise. The wiringdiagraffi shows how the very fewwires are placed in position, andprovided that all connectionsare firmly made (either bymaking a neat loop for inclusionbeneath the terminal head, or bysoldering to connecting lugs) thereceiver may be relied upon tooffer many months of efficientservice without risk of break-down. When wiring the receivercross out each wire on thewiring diagram as its counter-part is placed in the receiver,and thereby avoid the risk of

omitting one wire and dispose of all doubtas to whether any mistakes have been made.

The illustrations may be used as a guidein wiring, and every component required isclearly set out in the list of components onpage 641. Do not be tempted to use asubstitute if you cannot at -once obtain theparts named. Not only will the layout


A view of the underside of the Signet ready for Wirth;

August 29th, 1936 PRACTICAL AND AMATEUR WiRELESS

HESS96:ai. RADAO

PROGRAMME

aeat

Advt. of The General Electric Co. Ltd., Magnet louse, Ringsway, London, W.C.2.

639


001

Pentode for use in battery

"NOP 1057 /7,01. ie/ "ger //910011W/50,/ ////// 9//////.1//////////// // // // // // /./ //// //// /17.67/77/.51, /AY Z/AZ, ///71/// ////7/////7/.410% /WM% //- .////Z41//1/211111010.11191111200111/7"

/////////////,/////////////////////////////////////x,/////// ///////////, 49.11,1414.51/44,11V/14,44.1511.51M.91..1.4.1./.6441111////,/,,K614.11616./ .4.5111/1/4.1.109111/.611,141.1/1,11141,1,/,/,,,,,,,,1110.61.1.11.1011/ 1//4,11.11//

2 newBATTERYPENTODES

V.P. 210 PEN. 231A variable -mu screened H.Freceivers.The valve is specially constructed for use under conditionswhere freedom from microphonic noise is required.The anode -grid Capacity is only 0.004 mrnfd.

RATINGFilament Volts - - 2.0 Filament Current - 0.1Max. Anode Volts - - 150 Max. Screen Volts ISO TYPICAL OPERATING CONDITIONS

Mutual Conductance - 1.4* - 'Ahode Volts - - - - 120 Screen Volts -ot Ea120v. Es60v. EgO Grid Bias - - - - 2.5 Anode Current

-The bulb is metallised and fitted with a 7 -pin standard Optimum Load - 19,000

base. The valve is fitted with a standard 5 -pin base.

EDI SWAN reirA,0.i. MI

A high slope output pentode for use in battery receiverswith a self -biased circuitRATINGFilament Volts - - Filament Current - 0.3Max. Anode Volts - 150 Max. Screen Volts 150

Mutual Conductance - 5.3**at Ea100 E5100 EgO.

Fa/ details of these valves and others in the MAZDA range can be obtained on application to the Technical Service Dept.Mazda Radio Valves are manufactured in Great Britain for The British Thomson -Houston Co. Ltd., London and Rugbr, and distributed byTHE EDISON SWAN ELECTRIC CO. LTD., 155 CHARING CROSS ROAD, LONDON, W.C.2 R.M.292

ew

04r/174VASYGIN310111,1:8NEMEW,..117(4102174ENERr' 10711SMIZAVIAlEr

1205.0

a811111.

frezerom vie

THESE TWO COMPONENTSHorizontal Drive Type SL 9. Black or BrownBakelite Escutcheon with Air Dielectric Trimmer.Cat. No. 2135. Price 6/6.

Slow Motion Popular Log ratio 35-1. Cat:No. 1046. Price 7/6.

These two components, the Horizontal Driveand the Slow Motion Popular Log, both ofwhich are on show on the J.B. Stand at Radi-olympia, have been chosen by the Practical WirelessTechnicians for their two latest circuits. The formeris specified for the " Gladiator Three," and the latteris included in the specification of the " Signet Two."

A full selection of our condensers and dials is on viewon Stand 81 at Radiolympia. You can examine themechanism and make your choice.

'JACKSON Brothers (London) Ltd., 72, St. Thomas Street, S.E.1Telephone Hop 1837

RADIOLYMPIA

STANDroNo. 81


35/4M

/0

641

Panel layout decigram,(Continued from page 638)

probably have to be modified to accom-modate the alternative part, but the per-formance may be impaired due to differ-ences in characteristics.

The ChassisIf desired, a chassis may be obtained

already drilled from Messrs. Peto-Scott,from whom also a complete kit of parts for

LIST OF COMPONENTSOne coil (C20) (Bulgin).One .0005 mfd. condenser (1,046) (Cl) (J. B.).One .00025 mfd. reaction condenser (1,081)

(C2) (LB.).One L.F. coupler (Transfeeda) (Benjamin).One resistance : I meg., R1 (Erie).One .0001 mfd. condenser (665) (C3) (Du-

bilier?.

One switch (S36) )Bulgin).One switch (S22) (Bulgin).Two terminal strips, A.E. and L.S. (B. Lee).Two valveholders (one 4 -pin, one 5 -pin)

(Clix).Two valves: D210, Y220 (Hivac).Five plugs : H.T.--, H.T.I, H.T.2, G.B.+,Two spades : LT.+ (B. Lee).Four component brackets (P. Scott).Metaplex chassis, 10" by 6" by r (P. Scott).One 100 m.a. microfuse and holder (Micro -

fuse).One spealier, Type SD (Epoch).

this receiver may, be obtained. If such achassis is obtained the actual construc-tional work may be carried out with theaid of only a screwdriver and a pair of pliers.If a complete chassis is obtained holes willhave to be drilled in order to accommodatethe valveholders, the terminal socket stripsand for the various connecting wires to

pass through. There are nine of these,and a gimlet may be used for the purpose.Alternatively, a hole -kin. in diameter maybe drilled, but for the valveholders a holelin. in diameter must be drilled, and as aprecautionary measure the metallised sur-face round the hole should be scraped awayby means of a penknife in order to avoidrisk of short-circuits when the valveholdersare screwed into position. For the socketstrips you can drill either a separate tin.hole for each projecting socket, or may cuta slot into which both sockets on each stripwill pass. This is done by drilling two kin.

0A -A- Jiwrc..v

holes separated by a space of lin. andsawing away the intervening wood.

Before mounting the components oneimportant factor must be stressed. Theon -off switch is included in the L.T. positivelead and, consequently it must be insulatedfrom the metallised chassis which is con-nected to the L.T. negative lead. Themetal -mounting bracket, which is employedis screwed to the chassis, and the plunger ofthe switch is in direct contact with themounting bracket. Therefore, beforescrewing the bracket into position themetallised surface must be scraped awayfor a sufficiently large area to ensure thatthe foot of the bracket will be effectivelyinsulated. Again, a penknife will enablethis operation to be carried out quickly andefficiently.

Next week we will give further detailsconcerning the construction, together withoperating details.

Wiring Diagram of theSignet Two

`1 'E 0/AA/GE J7,-2,/ 7 CA,

.f2WAVDE ifiVAYAIETAZ.L /-T/NG

9

\0 0

r]

.41, 9 = ii 74It/SEO

f/7

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..t? /41.z-6,

Ammorift,..

-11

r-\1-1-1-11-1

4/1,co

211C000.z..S 4,F0i 1

6

YOUR SETT.___ 1936MAY NOW BE JUST I:THIS MUCH 36sBETTER F

r 1,,e+

1937


A Pre -Show View and ReviewBy W. J. DIELANL Y.

August 29th, 1936

CCOVQ1(Snand their

An Interesting Review' of the 4AIPDevelopment of the Modern Wireless Receiver, withSpecial Reference to Some of the New ModelsWhich will be Seen at This Year's Radiolympia

IN the early days of radio the apparatusused for the reception of the variousamateur and commercial trans-

missions was of a really crude nature.Mounted upon a flat baseboard (in manycases the domestic breadboard or pastry -board) and adorned with a weird collectionof home-made components, it reposedeither in the son's den, or was treasured byfather, and was not to be touched by

The loud -speaker opening on this Aerodyne receiveris neat, and gives the cabinet a distinctly effective

appearance.

anyone. When the broadcast programmesstarted, commercial components becamesteadily available, and the receiver beganto take on a new appearance. An endeavourwas made to enclose the " works " andprotect them from damage and dust.To enable advantage to be taken of theprogrammes which were from time totime available, the receiver bad to beinstalled in the living -room, and it generallytook a place of honour in front of a windowso that a short aerial and earth lead couldbe utilised. The loud -speaker was im-provised, and stood on the receiver or thetable, or, in some cases, was hung upon thewall.

Separate SpeakersAs improvements were made the receiver

became totally enclosed in a cabinet,generally home-made from any odd ply-wood, and the general appearance was notunlike a miniature coffin, the front arrayedwith controls of all shapes and sizes.

The development of the cone -type loud-speaker led to the, construction of cabinetsto accommodate this type of speaker, andthis took up its position near the receiver,

Other Interesting CabinetIllustrations will be Foundin Our Complete ShowReport, pages 623 to

637.

inetsand, in view of the general bulk, the privilegedposition near the window was > foresaken,and the equipment was provided with aseparate table in a corner out of the way.We may trace the.progress of the apparatusfrom this stage to the present day in manysteps, from the large cabinet enclosingboth speaker and receiver, with separatebatteries placed upon the floor or in anearby cupboard, to the floor model, orlarge type cabinet which now seems to bethe recognised home for the radio receiver.But those early cabinets were reminiscentof the Victorian piano, with their fret -worked fronts backed with gaudy piecesof silk. Do you remember the loud-speaker openings of those early days?Such motifs as rising suns, trees in thedesert, bird and cloud effects, and evenchildren hand -in -hand were carefully cutout, and, whilst perhaps appealing to sometastes, they did very little to improve thepoor reproduction of the loud -speaker, due,to the rattle set up by the split layers offretweod, and flap of silk against wood.To -day's Furniture

But to -day all this has changed. The radiooutfit is now rightly regarded as a musicalinstrument, and takes its place in the homeas an article of furniture in additionto this. A walk round the stands at thisyear's great exhibition will show that thecraftsman, the scientist, as well as theradio -technician, has been called in todesign the cabinet. Gone is the fretted

loud -speaker opening, and the thin three-plystructure which resonated at every note.In their place we find solidly -built cabinets,lined with non -resonant material, or other-wise divided up to avoid resonances;

In this receiver the loud -speaker opening has againbeen diverted from the vertical, but is curved,

and strikes a new note in design.

This is a Mallard receiver, in which the cabinet design follows the very modern trend of severe andstraight lines.


IT PAYS TO USE EDDYSTONEVISIT STAND 23

.getyour copy of the1937 EDDYSTONESHORT WAVE MANUAL

INTERCHANGEABLE COILSNew low loss formers of DL -9 high -frequencyinsulation. Rigidly made and each coilmatched. First class results assured.- 4 -pincoils have two windings. 6 -pin three windings.NO. 9596 -pin Set -of 4 12-170 metres Price 16/.No. 932 4 -pin Price 14/.

AIR TUNED I.F.TRANSFORMERSCompact unit withhigh efficiency airtrimmer and genuinelitz wound coils.Total tuning coverage400 to 500 Kc/s.Gives high stage gainwith approximately 9Keit. band -width.Nc. 1.014, 450 kch,

Price 13/6.

UNIVERSAL S.W. VALVEHOLDERMIDGET INSULATOR A low loss holder for above or below baseboard use.

for The valve enters the contacts from either side.Made from Frequentite r Therei no measurable increase of self -capacity tometal parts. lin, overall.height. that aheadin the valve base. DL.9. H.F. dielec-high- frequency work,with N.P.

No. 1019. Price 411 each. trio, one -prate noiseless contacts.No.1015. 4 -pin, 1/3. No, 1016 5 -pm, 1/3.

No. 1024. 7 -pin, 1/8.

ULTRA SHORT-WAVE H.F. CHOKES.These chokes are single layer space woundon DL -9 formers, and have an exceedinglylow self -capacity. 21-10 metres.No. 1011. D.C. Resistance 1.3 ohm,. Price 1/3No. 1021. D.C. Resistance 0.4 ohms. Price 1/3

FLEXIBLE COUPLERFree from back -lash but veryflexible, this coupler banishesalignment troubles. DL.9,H.F. insulation. For fin.

spindles.No. 1009. Price 1/.3.

N

IMPROVED MICRODENSERNo. 900.

For ultra H.F. and general S.W. useCALIT insulation, !ow series resist-ance, noiseless movement, extendedLin, spindle for ganging.20 romfcl., 3/9 ; 40 in.mfd., 4/3 ;

100 m.rnid., 5/-.

BANDSPREAD TUNING OUTFIT.Devised to simplify station selection.

The Tank con-denser unit has

a capacityrange et1 0 x 14

mrnfd. Achievedby a patentedstep by step

device. Complete with scale and knob.Tank Unit :

Cat. No. 1042. Price 6/.

In parallelwith t h eTank capa-city is he

slow motion135 ndspread

Trimmer con-denser, with a capa-city slightly greaterthan each step by

step of the Took condenser.,Complete with dial. Trimmer Unit:.Cat. No. 1043. Price 6/C.

SHORT WAVE COMPONENTSSTRATTON & CO., LTD. Bromsgrove St., Birmingham. LONDON Service Depot: Webb's Radio Storrs, 14, Solo Street, Oxford Street, W.

zc

TUNGSRAM VALVESEXCLUSIVELY SPECIFIED

Listed below are the only valves specified for the new "BandspreadS.W. Three" details of which are given in this issue. All are 2 volt

battery valves. All are Tungsram !

H.P.211 H.F. PENTODE . . . 4 PIN .. .11/-H.P.210 H.F. PENTODE . . . 4 PIN . . .11/-P.P.222 OUTPUT PENTODE . 5 PIN . . .10/-

TUNGSRAMMANUFACTURED INTOTTENHAM LONDON Barium VALVES

THE TUNGSRAM ELECTRIC LAMP WORKS (GREAT BRITAIN) LTD., 7 2 OXFORD ST., LONDON, W.I. PHONE: MUSEUM F,CF.3.

644 PRACTICAL

RECEIVERS AND THEIR CABINETS(Continued from page 642)

special loud -speaker mountings to produceevery note in the musical scale with equalfidelity ; special materials covering aclean-cut opening for the speaker, and,in many cases, a complete absence ofknobs, switches, and other projections.

Look at the H.M.V. receivers, in whicha complete departure has been made' fromall standard practices. The loud -speakeropening is not even flat, but is neatlycurved to enable the speaker to be mountedat an angle and direct the sound waves ina more useful manner, and to provide atthe same time " something different."Special metallic gauze covers the openings,and in one case three separate speakers facein different directions, and thus coverevery part of the room with their radiations.

This

August 29th, 1936

Utility ApparatusMany radiograms are

used as a convenient placefor the placing oft bowl offlowers or a small electricstandard -lamp. Cons e-quently, when it is desiredto reproduce gramophonerecords, these articles mustbe removed to open thelid. Again, H.M.V. havecome to the assistance ofeveryone by designing acabinet on the lines of anordinary writing bureau,and the top does not haveto be lifted, the slopingfront lowering to reveal thecontrols, turntable, etc.

In two or three cases wemassive cabinet was designed for the Self -Changing Gramo- find that well-known per -

phone Company by Robert Lutyens, sonages have been calledin to assist in the design of. -

AND AMATEUR WIRELESS

HIVACHARRIES

THE WORLD'S BEST OUTPUT VALVEThe Triode, hitherto, has yielded

quality wilh low sensitivity.

The Pentode type left much to be

desired in quality, but gave sensitivity

-whilst the advent of the HIVAC

HARRIES valve combines the quality

of the triode wiih the sensitivity of a

pentode because the suppressor grid

has been removed and the anode

set at a "critical distance."

This remarkable technical achievement

approximates to the ideal requirements

of the perfect output valve.

The illustration shows the manner inwhich the electron stream is "focussed",in HIVAC Harries " critical anode dis-tance " output valves. The latest andgreatest development in valve design.

SIMPLY PLUG IN A HIVAC HARRIES AND CET GREATER VOLUME IMPROVED TONAL BALANCE INCREASED CLARITY OF REPRODUCTION

PRICES FROM

16c

9 THE SCIENTIFIC

STAND 26RADIOLYMPIA

VALVE

BRITISH ,51

There is a HIVAC

OUTPUT VALVE

to suit every set.

A fs:ur coloured Illustrated Folder "PRIV on HIV -IC Harries Output Valves. FREE for P!C or Telephone request.

HIGH VACUUM VALVE CO., LTD., 113-117, FARRINGDON RD., LONDON, E.C.1,

a cabinet which may be itself regarded as awork of art. In the Self -Changing Gramo-phone Company's console model the well-known architect, Robert Lutyens, F.I.A.A.,was responsible for the cabinet design, andthis particular model is illustrated on thispage.

Moulded CabinetsBut cabinet -work has taken on a different

atmosphere in the Ekco models, wherebakelite has been employed, and this ismoulded by a special high-pressure process.Again, special experts have been called into assist in obtaining cabinets which maybe placed alongside modern furniture, andone of this year's special Ekco models hasbeen designed by Serge Chermayeff, and isan artistic production in black, with ivorycontrol knobs.

Television ReceiversBut the forthcoming production of

receivers for the reception of the televisionprogrammes necessitates the inclusioneither of the screen of the cathode-ray tubeon the front of the cabinet, or, as in thecase of the H.M.V. receivers, of a mirrorinside the lid, which has to be raised at anangle of 45 degrees in order to reflect thetop of the cathode,ray tube which is placedin a vertical position. These particularmodels, together with some other interest-ing examples of the modern wireless receiver,are illustrated in our Complete Guide tothe Show, which is given on other pages inthis issue, and the home -constructor iscatered for by several firms who nowspecialise in the production of cabinetswhich may take their place with the modernhome furnishings, and no longer give to theradio receiver the appearance of a scientificpiece of apparatus which was in the pastregarded as " something uncanny."

NEWNES'

TELEVISION AND

SHORT - WAVE HANDBOOK i2nd Edition

By F. J. CAMM.

Price 3/6 or 3/10 by post from the Pub-; lishing Dept., George Newnes, Ltd., 8-11,

Southampton St., Strand, London, W.C.2.

Telephone : CLErkenwell 7587.


This is a selection from theAN EXPERIMENTER'S TEST BENCH(Continued from page 604)

provided with six terminals -for aerialand earth, loudspeaker and low-tensionleads, and with Clix sockets for the grid -bias and high-tension connections. Thejacks are arranged between the terminalsand sockets, those for current readingsbeing above the centre line, and thosefor voltages being below, as indicated.This ebonite strip can be attached to theback of the bench, and should preferablybe covered in at the back so that straywires cannot fall on the terminals andconnections and so cause short-circuits.

Another refinement consists of a .0003-mfd. bakelite-dielectric condenser, mountedbetween the aerial and earth terminals,and connected in series with the -aerial

; this can be used for varyingthe degree of selectivity when the set undertest is not provided with a series -aerial.condenser. If a D.C. mains unit is em-ployed for H.T. supply, another refinementmight consist of a 1-mfd. fixed condenserwired between the earth terminal on thepanel and the earth lead.

An Output FilterThe idea of using the loudspeaker ter-

minals on the panel is that a standardloudspeaker, placed in what has been foundto be the best position in the room, can bepermanently connected to them. Thespeaker should preferably be fitted with atapped matching transformer, but analternative is to mount a choke -capacityoutput filter on the panel, connected asshown in Fig. 3. It will be seen that thetwo ends of a tapped output transformerare connected to the two speaker terminalson the panel, the speaker itself being con-nected to any one of the other terminalsby means of a flexible lead with spadeterminal, and also to one terminal of a4-mfd. condenser, the other terminal ofwhich is joined to the earth terminal onthe panel.

Reverting to the meter and its plug, itis best to connect a .1-mfd. non -inductivecondenser in parallel with the meter toact as a by-pass when current readingsare being taken. If this were not doneinstability might be introduced due to thecomparatively high resistance of the meter.The meter can then be mounted on a suitablebracket above the test panel or arrangedto hang from a hook on the wall. Inany case it will be found convenient toarrange yet another open -circuit jackon the panel, and to attach a couple ofleads with . test prods to this. Thenany measurements which have to be takeninside the set, or when testing components,can be taken simply by inserting the meterplug into the " spare " jack and using thetest prods in the normal manner.

ModificationsThe general arrangement which has been

described can be modified in various waysto suit individual requirements, and itwould be a perfectly simple matter to includeadditional jacks for extra H.T. and G.B.leads. Those who have an output meterof some kind could also arrange to plugthis into a jack connected to the loud-speaker terminals. In the case of mainsoperation some of the leads might carry

thatin which case it must be remembered

that an A.C./D.C. meter would be necessaryin order to take all measurements. Gen-erally speaking, however, the system ismore suitable for battery -set users, andunless the reader has a fair knowledgeof electricity he is not advised to attemptto modify it for use with mains sets.

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645

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SHROUDEDPLUGS AND

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FUSE PLUS.B.S.S. and R.C.M.F. specifi-

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CARTRIDGE FUSES.1+ in., 1 in., (linstandard specifications,colour coded, 60 m/A to 3 amp., all one price, 6d.A lso "Scrufuse," for bulb type holders. same price.FLEX FUSEHOLDER. -

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FOR short-wave reception simple appar-atus is very popular, arid, if intelli-gently operated, w ill provide world-

wide reception under average receivingconditions.

Choice of receiving apparatus is largelygoverned by individual requirements andcircumstances, both of which are apt topresent the set designer with some difficultproblems to solve, in order that all tastesmay be catered for in a satisfactory manner.

evs

A B.T.S. 3 -range dual S.W. coil unit fitted with rotary switchingdevice.

For example, one enthusiast favours astraight two or three-valver, and judgingby the colossal logs compiled by many whouse this type of, receiving apparatus, thereis no doubt that very satisfactory resultsare obtained.

On the other hand, sorpe enthusiastsfavour the superhet, owing to its superiorselectivity, and others, whilst in agree-ment in matters of selectivity, considersupers to be noisy, everything else unselec-tive, and await the ideal receiver withsuper selectivity, and a one -valve noiselevel.


SHORT WAVE_SECTION

Further Notes for S. -W. ExperimentersAmong the Subjects Discussed in This Article are Aerial Coupling, Aerial

and Earth Systems, and Tuning Units By A. W. MANN

The Straight Two and Three-valverThe straight two and three:valve type

of receivers are comparatively unselective,but in the light of personal experience,not as unselective as many would have usbelieve. When a receiver of this type isso unselective that reception on all bands isdevoid of any pleasure at all, it is clearthat the circuit fundamentally is not atfault, but that the constructor is largelyresponsible.

For example, short-wave coils as we knowthem to -day all look very much alike ;nevertheless, they are not when perform-ance is taken into account, and if it werepossible to take a census amongst themost successful DX enthusiasts who usestraight receivers, I think it would be foundthat coils of high class make and first ratedesign are used by the majority. -

Aerial CouplingsNext comes the question of aerial

couplings, which mays beaperiodic or- capacitative.Fortunately, the present dayconstructor cannot go farwrong when the formermethod is used, due to thefapt that the couplingbetween the windings isfixed.

Thus it will be appreciatedthat when aperiodic couplingis used, first class coils aremost desirable, otherwise,once absorption and associ-ated troubles are experi-

enced a remedy under the existing circum-stances may be hard to find.

Another point sometimes, overlooked,especially by those who wind their owncoils, is that the distance hetween the gridaad aperiodic windings, also the number andspacing of the turns of the latter, have agreat bearing on the selectivity.

As we have only one tuned circuit, it isnecessary to strike a compromise. Imaginethat the aperiodic winding is movable, infact a separate coil unit as in the old days.

First couple the aperiodic and grid coilsas close together as possible ; volume

be satisfactory, but selectivity poor, whilstinstability may be expected.

In order to improves selectivity, it isnecessary to slacken the coupling betweenaperiodic and grid coils, and strike a happymedium which will assure average selec-tivity and volume with stability. It willbe appreciated, therefore, that when home -constructed coils are contemplated, it is-advisable to work from published data.

Aerial series -capacity coupling is verymuch in favour nowadays especially withbeginners. The latter, however, some-times strike trouble when first putting thismethod in use.

They find that by screwing the '0001(Continued overleaf)

1111111A1ud111II II

I

1111111SW IIII1111111

IIIIIIaIIII.IIlllilll fil lII

I li1111111111.IIII

A three -range air -spaced short-wave coil by Bulgin.

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816Intermediate Frequency Transformerfor 465 k.c. Fixed Coupling isemployed with Mica Trimming con-densers and Litz -wound iron -coredcoils. Price 8/6.

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BP 112 Superhet model with Inter-mediate Frequency of 465 k.c. 1316.BP 114 Straight model having oneH.F. Valve. 13,16.

As in previous years the Varley company haveproduced another interesting range of efficientcomponents for the home constructor.Old friends, such as the Permeability tuner,are on show and in addition the three newcomponents shown here. All three have causeda considerable stir in the radio industry andthey are assured, by their low price andefficient action, of a record sale to the homeconstructor.Come and see them on Stand 77.

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SHORT-WAVE SECTION(Continued from previous page)

mfd. pre-set condenser right down, maximumvolume is obtained. Selectivity, however,will be poor, and it is undoubtedly true tostate that instability, threshold howl, andbody capacity effects in modern straightcircuits as used by beginners, are, in themajority of instances, directly due to tightaerial coupling.

A little time spent in trying varioussettings of the pre-set condenser until aposition is found which enables optimumvolume and selectivity on all ranges to beobtained, is well worth while.

Here again well designed coils willprove to justify their cost, because a settingwill be found which will provide the desiredresults no matter which coil is in use, andthe pre-set condenser can be firmly lockedin position. This is a most desirablefeature when direct tuning dial calibrationis contemplated.

Aerial and Earth SystemsApart from the above considerations

there is another, which has a bearing on theselectivity problem, i.e., the aerial andearthing systems. How many use longaerials and poor earthel Even a single wireaerial designed on scientific principles willprovide better results than a haphazarderection.

In many instances anything given thename of an earthing device is consideredsuitable for short-wave requirements.Copper -plated metal tubes, for example,whilst satisfactory for broadcast purposes,are in some instances unsatisfactory forshort-wave use. Examination of suchdevices after a few months use, showsthat the copper covering no longer exists.A tube of solid copper, a length of solidcopper rod, or a copper earthing mat arethe most satisfactory. On the other hand,it is sometimes found that a battery -operated short-wave receiver, functionssatisfactorily without an earth.

Interest and attention is now being paidto experimental all -wave receivers. Experi-menters have their own ideas as to whatconstitutes an all -wave receiver.

On the one hand is the amateur whofavours the plug-in coil system, and onthe other those who favour speciallydesigned tuning units. When the plug-incoil method is used, selectivity on thebroadcast bands is relatively poor.

The reason for this state of affairs isdue to the unsuitable ratio of inductanceand capacity. The standard tuning capacityfor broadcast reception and around whichmedium and long -wave tuners are designed,is .0005 mfd., and the most suitable valueof tuning capacity for short-wave use, iseither .0001 mfd. or .00016 mfd., accordingto the make of coils used. Thus, in orderto cover broadcast wavelengths, a coilfor use with such low capacity tuningcondensers contains a greater number ofturns than when the higher capacity is used.

As a result, we have a high inductanceand low capacity ratio which, due to broadtuning, provides very poor selectivity.All -wave tuning on the above lines cannotbe otherwise than a compromise.

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WITH the continualincrease in the numberof South American and

other distant stations reportedin various quarters, one is apt tolose sight of the great develop-ment taking place in the Euro-pean short-wave network, whichincludes many powerful trans-mitters giving broadcasts easilyreceived by the owners of themore modest one and two -valve sets. Asa rule, the tyro who takes up short-wavelistening, in his anxiety to log distanttransmissions is liable to miss much ofinterest nearer home, and it would bewise, if disappointment with the newreceiver is to be avoided, to try at the outsetfor some of the short-wave broadcastsregularly put out by the Continentalstations. Without turning to Colombia,Venezuela, Canada, Cuba, Costa Rica,it is possible in this manner to compilea very respectable log in the course of afew hours on most evenings, as identifi-cation by means of the musical intervalsignals, and the oft -repeated calls in variouslanguages, has been made much lessdifficult than it was a year or so ago.

Germany's Extra StationsDuring the period of the Olympic Games

the ether was full of broadcasts carried outby Berlin, and no doubt some of the extrastations brought into action for the purposeof transmitting commentaries and reportsof results to foreign countries interestedin the competitions may be used again inthe near future. Here are three powerfultransmitters which were on the air inaddition to the regular numerous DJ,Zeesen stations : DZC, 29.16 m. (10,290kc/s) ; DZB, 29.87 .m. (10,042 kc/s) ; andDZA, 31.011m. (9,675 kc/s.), all situated atZeesen, and as a rule solely employed incommercial telephony or relays of pro-grammes for re -broadcast abroad.

And Now SwedenThe Stockholm short-wave station to

which I referred recently in these notesnow appears to have adopted a regularschedule; is is rn the air daily on 25.63m. (11,705 kc/s) from roughly "B.S.T.17.00-23.00 with a relay of the Stockholm-Motala programme. On Wednesdays aspecial transmission is made for Swedishlisteners in North and South Americafrom B.S.T. 23.00 until midnight. Onsome nights from the closing -down timethe station reverts to its amateur status,and, under call -sign SM5SX, works on14,341.2 kc/s-namely, in the 21 -metreband. The Swedes as a nation are goodlinguists ; from the Stockholm short-wavetransmitter you will hear announcementsin Swedish, German, English, Spanish,French, Italian, and Russian.

Oslo Follows SuitOslo will be shortly testing the new

25 kW. Jeloy short-wave station on 31.48m. (9,530 kc/s) with special programmesfor listeners outside Europe. Identificationwill be facilitated by the fact that theannouncer will give call and details ofprogrammes in both Norwegian andEnglish. To finance these extra trans-missions, which are to consist of half-hour broadcasts from B.S.T. 00.00-03.00daily, sponsored programmes will be givenadvertising Norwegian goods suited to theexport trade. Care must therefore be takennot to take the Norwegian transmissionsfor some emanating from the UnitedStates.

[Leaves from alShort-wave Log

A New Portuguese ChannelLisbon, with the call Emisora Nacional,

has been heard trying out gramophonerecords and speech on a condenser readingimmediately below that of 12R0 Rome ;although I have not yet secured confir-mation I take it that the broadcast is on25.36 m. (11,830 kc/s), a channel used lastyear by CT1AA, Lisbon, and later aban-doned for its present frequency.

Extended Russian BroadcastsAgain Moscow transmitters have altered

their timing of English programmes ; wenow find RW96 on 19.76 m. (15,18) kc/s)with a Sunday transmission at B.S.T. 16.00and another one at 19.30. RNE, on 24.99m. (12,005 Ire/s), takes the air on Sundaysat B.S.T. 16.00, every week -day at midnight(S.B. on 31.51 m.-4,520 kc/s), and onWednesdays give a special talk at midday.

The Lesser Reported Jugo,:,slavianBelgrade (II), on 49.18 m.

(6,100 kc/s), 250 watts, givesout broadcasts which a.re nowclearly he'ard in most parts ofGreat Britain. This station worksfrom B.S.T. 17.30-22.30, and 1

occasionally again after 23.00 foran hour or so. The woman

announcer repeats the call at every,possible opportunity in French, Italian, Ger-man, Magyar, Greek, Albanian, and Serbian.Dutch Programmes for America

PCJ, Eindhoven (Holland), on 31.28 m.(9,590 kc/s), may be heard every Monday,between B.S.T. 01.00-02.00 and everyThursday from B.S.T. 01.00-04.00 with avery good wireless entertainment mainldestined to the United States. Mr. Startz,the announcer, leaves you in no doubtregarding the origin of the programme, ashe repeats his Dutch announcements inEnglish, German, French, and Spanish.More Transmissions from Schenec-

tadyW2XAF, on 19.56 m. (15,330 kc/s), has

extended its broadcasts by nearly two hoursdaily ; the. station now gives a continuoustransmission from B.S.T. 16.00-21.45, whilstW2XAD, on 31.48 m. (9,530 kc/s) continuesto transmit from B.S.T. 22.00-06.00.

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LETTERS FROM 'READERSThe Editor does notnecessarily agree withopinions expressed by his

correspondents.

S.W. Reception in Aberdeen

SIR,-Perhaps some readers would be

interested in the following list ofrecently verified reception as I have notseen a published S.W. log from this district.

Empire broadcast to Africa, 49 metres ;time, 8.0 p.m. B.S.T. Saturday, August 1st,1936. Radio Coloniale, F.Y.A. ; time,8.0 p.m. Sunday, August 2nd,. 1936: DJE,DHB, DUB, Germany calling China ; time,11.50 a.m. Calls in English every minuteuntil 11.59 a.m.


tion).

The set used was a B.T.S. InternationalS.W.-receiver. Aerial 25ft. with 25ft. leadin. With headphones reception was veryclear. -E. LEASK (Aberdeen).S.W. Superhet

SIR,-I should like to add my appeal

to those you have already receivedfor a short-wave superhet. I suggest abattery -operated four -valve set using plug-in coils, preferably of the six -pin type.

In such a set I should like to see sensiti-vity given the first consideration. As some

PILOT MODEL U.6506 Valve Superhet Receiver covering4 Wave -bands (16 to 2,100 metres).

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PILOT RADIO LIMITED 87PARK ROYAL RD., LONDON, N.W.10

August 29th, 1936

people are interested in C.W. reception theinclusion of a beat oscillator should beoptional. I am at present using a det.-2LF set, and should like something moreelective. -E. Cox (Bishopstoke, Hants.).

Automatic TuningIR,-I have seen on some commercialS - receivers a device by which the sot

automatically pulls itself into tune, whenthe hand is removed from the tuning knob,provided that the tuning is approximatelycorrect. Please could you explain theworking of the above device, or inform mewhere I could obtain details ?-R. A. H.KENT (Northallerton, Yorks).

[An article dealing with this subject appearedin PRACTICAL AND AMATEUR WIRELESSdated November 9th, 1935. -ED.]

A Good S.W. LogSIR, -I enclose my log, which may

interest other S.W. listeners.Broadcasting stations : GSC, DJA, 2R0,

RW59, VP3MR, GBTT, HBP, HBL, EAQ,KVJ, W1XK, W2XAD, W3XAL, JVH,JVM, OXY, CKAA, VK2ME, TFJ, PHI,W2XE, OLR, W8XK, TPAC, GBZW, andR. Belgrade.

Two a.m. phone : SM5SX, G6LB,W1MX, W1VJ, SU1SG, . F8NG, W2SA,W2MJ, W2E0, W2BTV, W1BIC, W2EIO,SU1CH, VE2PJ, OM2MJ, W8CMA,W8DW,W1AXA, W3EAI, W1SLO, W3GPP,W2FS, WICH, W3EAO, W5XG, W3CP,ON4PA, PY2BA, G5ML, G6LL, G2FC,G2FJ, SUISD, and SUIKG.

Eight a.m. phone : PAOPMR, ON4SS,and PAOSV.

My receiver is a .home-made 0-v-1with a 70ft. aerial of a single strand. -E. Wnalarsow (Alford, Lines).

Public Schools Expedition to Finland

SIRbrother, J. R. S. G. T., is inof W/T morse, on 20, 40, andCIVaMrgye

80 metres with the Public Schoolboys'Exploration Society's expedition in Lap-land, and should be " on the air" till aboutSeptember 14th, working from 11' to 11.30p.m. (B.S.T.).

British and other transmitters are invitedto try and make contact with them. Theyare, I believe, about 500 miles away fromrail and road, in the extreme north ofFinland. -CHRISTOPHER TAYLOR (Derby).

[Further particulars of this expedition weregiven in our issue of August 22nd, p. 573. -En.]

Light Entertainment from Weston -super -Mare

THE Show of Shows," presented byGeoffrey Hope and Vivian Palmer

and produced by Vivian Palmer, will beheard in a, broadcast from the KnightstonePavilion, Weston -super -Mare, on September4th. This is the second opportunity whichWestern listeners have had this season ofhearing " The Show of Shows " from theKnightstone Pavilion, the previous broad-cast being given on July 10th.

The Editor will be pleased to consider articles of apractical nature suitable for publication in PRACTICALAND AMATEUR WIRELESS. Such articles should bewritten on one side of the paper only, and should containthe name and address of the sender. Whilst the Editordoes not hold himself responsible for manuscripts, everyeffort unit be made to return them if a stamped andaddressed envelope is enclosed. All correspondenceintended for the Editor should be addressed : The Editor,PRACTICAL AND AMATEUIt WIRELESS, George Newnee,Ltd., 8-11, Southampton Street, Strand, W .C.2.

Owing to the rapid progress in the design of wirelessapparatus and to our efforts to keep our readers in touchwith the latest developments, we give no warranty thatapparatus described in our columns is not the subject ofletters patent.


PRACTICAL TELEVISION(Continued from page 614)

Lewis's Concert Hall, where a chamber largeenough to accommodate two people togetherwith the associated lighting and scanningequipment was erected for the purpose.Details of the method used are being kepta close secret at the moment, but accordingto one newspaper report arrangements arebeing made to install apparatus in Francefor use in conjunction with a broadcastingstation.

Spain RejectsIn Spain recently an effort was made by

two engineers to secure the requiredauthority for setting up a television station.This was, however, refused by the Ministryof Communications, since any form of radiotransmission is an exclusive service of theState. It devolves upon the radio adminis-tration for providing any service of tele-vision, and this can only be undertakenon some competitive basis. No doubt thisis meant to infer that a committee of investi-gation would have to be set up on linessimilar to that of this country before anyfinal concession was awarded. Bearing inmind the turmoil which at present existsin that country, there seems little likeli-hood of Spain undertaking any work of thisnature for some time to come.

The U.S.A.Some of the evidence placed before the

United States Federal CommunicationsCommission has been dealt with in thesenotes, and it is now interesting to refer tothat detailed by Mr. Jolliffe on behalf ofthe R.C.A. Quite rightly, he pointed outthat no system of television could properlyjustify itself until it had undergone themost stringent field tests prior to commer-cialisation. After trying out a number ofmethods, concentration was now being madeon the iconoscope, the present standardsof test transmission being one of 343 lineswith 60 frames per second interlaced togive thirty complete pictures per second.Carrier frequencies of 49.75 megacycleswere employed for the vision signals, andfifty-two megacycles for sound during thecourse of the New York tests, but it wasfelt that this did not in any way representthe final ones which would be acceptableto a critical public requiring perfect hometelevision entertainment. Good televisioncould be embodied in a band width of sixmegacycles (three magacycles maximummodulation frequency), and any effort towork below this figure would only reducepicture quality to an unacceptable standard.Figures were also furnished for the optimumviewing distance from the picture screen,this being given as approximately four timesthe screen height. Screen brilliance andcolour must also have a direct bearing onthis quantity, however, and further testswill have to be undertaken in conjunctionwith line definition and the picture repetitionfrequency.

Other important questions dealt withby Mr. Jolliffe concerned the relation be-tween service range and interference range.It was conceivable that the latter may beanything from five to ten times the former.To secure an adequate ether allocation forfrequency channels the possibility of whollyor partially suppressing one side -band was,considered, but many more tests will haveto be undertaken before any kind of decisioncan be arrived at on this question. Experi-ments conducted in the U.S.A. confirm thosecarried out by the Baird Company in thiscountry; namely,that forsatisfactory picturereception a signal strength of one millivoltwas sufficient. Below this figure results'could still be satisfactory provided the

receiver or the aerial was remote from anypossible form of interference, factorswhich could very readily be settled on sitewithout much difficulty. Another factorto come under discussion concerned thedistribution of programmes. It was pointedout that as far as America was concernedno network of cables capable of handlingthe video frequencies of television signalswas available, although installations of aco -axial cable had already begun. On theother hand, the direct relaying of pro-grammes by means of directional micro-wave links was feasible and further workon both these methods would have to beundertaken. A careful watch was beingkept on the work being carried out in theprincipal European countries, it beingstressed that carrier frequencies betweenforty and fifty megacycles were beingcentred on by those authorities concernedwith the provision of any form of ultra -

short -wave, high -definition television ser-vice, whether for experimental work orcommercial exploitation.

FROM THE PUMP ROOM,LLANDRINDOD WELLS

WELSH listeners will hear a new com-bination of broadcasters for the

first time on August 31st. Violet McDermottand her Orchestra will give a Recital fromthe Park Pump Room, Llandrindod Wells.Walter Glynne (tenor) will be the soloartist. The leader of the Orchestra isAnna Janssen, who, as her name suggests,is of Norwegian descent. The secondviolin is Peter Rosetti, daughter of JulianRosetti, the Polish pianist. The 'cellist,Paula Wilcock, has broadcast from theNorth Regional on several occasions andwas until recently a member of the ScottishSymphony Orchestra.

NEW LINES AND NEW LISTS

NOW READY FOR YOUTwo entirely revised two-coldurfolders, in which new lines areillustrated and described inaddition to the large range ofperfect -contact components forwhich Clix are renowned, areyours for a post -card request.Please ask for Folders " N."

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DIIERIESNQUIRIES

Second Channel Interference"I have repeatedly come across the

expression second channel interference "when dealing with superhets, and wouldlike to know just what it means. Also Iam considering taking up radio engineeringas a career, and would like to know thebest way to go about it."-G. S. M. (Roch-dale).SECOND channel interference is the

name applied to the whistles -whichare experienced in a superhet receiver andwhich are due to the generation of a beatnote between the station to which thereceiver is tuned and other powerfulstations which have a wavelength of sucha value that harmonics fall upon thedesired station. That is to say, whenreceiving a station at 400 metres, a powerfulnearby station radiating on 200 metreswould set up a second channel whistle, asthe first harmonic of 200 metres is 400metres and this coincides with the stationbeing received. The only satisfaCtory wayto avoid this trouble is to fit selectivecircuits before the frequency -changingstage, and whilst a simple band-pass aerialtuner in the grid circuit of the frequency -changer will do much to avoid the trouble,when situated very close to powerfultransmitters, the only effective remedy is touse a signal H.F. stage with sharply tunedcircuits. One of the well-known trainingcolleges can provide you with details of acourse suitable for your requirements.

L.F. Couplings"I use transformer coupling between

the detector and L.F. valve, and alsobetween the L.F. and output valve. I wantto know if it would be all right if they wereparallel -fed as shown in the Beginners'Supplement in your August 8th issue, asthey are cheap transformers. Also, wouldit be permissible to use zinc sheet insteadof aluminium on the baseboard? "-R. C.(Belfast).IT would certainly prove better to use the

parallel -fed method of coupling withcheap transformers, but, generally speaking,when using two similar couplings in succes-sive stages, it is worth while mixing thecouplings. That is, use straight transformercoupling in one stage and parallel -fed inthe other. The order to be adopted willdepend upon the H.T. available, and toenable the detector to receive sufficientH.T. for smooth reaction control and givegood rectification the transformer could beincluded as the first coupling. The L.F.valve must then be of .the type which willoperate with a low anode current, or thevoltage drop through the anode resistance

a

will prevent the valve from handlinga very large signal. You shouldtherefore experiment in your particularcase and find which combination pro-vides the maximum performance. Zinc

sheet or any other metal, provided it isnon-ferrous, may be used for screeningthe H.F. circuits, and, as pointed out lastweek, the metallised chassis used by us aresprayed with zinc.

Winding Broadcast Coils"I wish to wind a small coil to cover the

medium waveband tuned by a .0005 mfd.condenser, with a reaction winding, to usein a straight three designed solely for qualityreception of the local programmes. What

RULESWe wish to draw the reader's attention to thefact that the Queries Service is intended onlyfor the solution of problems or difficultiesarising from the construction of receiversdescribed in our pages, from articles appearingTh our pages, or on general wireless matters.We regret that we cannot, for obvious reasons-

(1) Supply circuit diagrams of completemulti -valve receivers..

(2) -Suggest alterations or modifications ofreceivers described in our contem-poraries.

(3) Suggest alterations or modifications tocommercial receivers.

(4) Answer queries over the telephone.(5) Grant interviews to querists.

Please note also, that queries must be limitedto two per reader, and all sketches and draw-ings which are sent to us should bear thename and address of the sender.Si a postal reply is desired, a stamped addressed envelopemost be enclosed. Send your queries to the Editor,PRACTICAL AND AMATEUR WIRELESS, GeorgeNantes, Ltd., &II, Southampton Street, Strand,

London, W.C.E.

number of turns should I require on aformer lin. in diameter for tuning and forreaction ? Also, what number of turns ineach case on a former of liin. diameter ?I make these small diameter dimensionsbecause I wish to make the set as compactas possible."-H. R. (Shipley).

AS you only wish to cover the mediumwaveband for the reception of the

locals, your coil should include the NorthNational and North Regional, and thereforemust tune from 261.1 to 449.1 metres.Allowing a small margin at either end, thecoil may be wound to cover from 200 to500, in which case an inductance of approxi-mately 175 microhenries would be required.This could be obtained on a 1 in. former bywinding on approximately 90 turns of 34gauge enamelled wire. On the liin. dia-meter former you would need only approxi-mately 80 turns. For reaction purposes 35turns of the same wire should be wound inthe same direction and separated about/in. from the " earthed " end of the formerwinding.

Faulty H.F. Chokes" In most wireless receivers I notice that

August 29th, 1936

an H.F. choke is put in the plate circuit ofthe detector valve, and this I am told isto prevent the H.F. currents from gettinginto the L.F. side to prevent distortion. 1

have a receiver that was faulty-a terriblenoise being emitted with the signals. 1

put this right by shorting the H.F. choke,and the set is now O.K. Also, in anotherreceiver the H.F. choke was taken out,replaced by a resistance of 20,000 ohms andI had no more trouble. Probably you couldexplain this, seeing that they both nowfunction better without the choke."-H. M. (Cawthorne).

THE trouble may be put down to one oftwo things. Either the H.F. chokes

were inefficient due to insufficient turns,or they were so placed in the receivers thatinteraction took place between them andsome other component-probably the tun-ing coils. This latter effect would beexactly the same as the normal reactioneffect, and thus the receiver would be in astate of oscillation all the time, producingdistorted signals. If the choke had in-sufficient inductance, it would fail to actin the correct manner, and could just aswell be omitted. By purchasing a goodmake of component this factor may betaken care of, and if the choke is of thescreened type, the casing should be earthedin order to provide the necessary screeningeffect. Alternatively, the choke may bewound astatically to restrict the field andavoid interaction with other components.

Grid Insulation" I have built a mains R.C.C. amplifier

but experience severe distortion. I havemade various tests with such meters as Ihave in my possession, and the only defectI can locate is that the anode currents ofthe L.F. valves are higher than they shouldbe by the valve data. I have checked thegrid bias circuits (these are automatic) andthey appear in order. Is it possible to giveme any assistance to locate the trouble fromthese details? The distortion is apparentthroughout the entire musical scale andespecially on speech, unless the volume isreduced to a very low level."-G. I. L.(Cardiff).

THE fact that the anode current is highwould indicate either that the H.T.

applied is greater than you think, or thatthe G.B. is lower than it should be. Asthe latter point has been checked and foundin order, and we presume that the H.T. ismore or less correctly arranged, the onlycause of the trouble must be that in someway the G.B. voltage is reduced or nega-tived. This can be caused by a leakycoupling condenser, and as the amplifieris a mains model you may have usedcoupling condensers which are not designedfor the high voltage working, and as aresult a positive potential is being applieddirect to the grid. This will result in dis-tortion, and, in addition, the increased anodecurrent may be resulting in an overloadof some other component which has beenselected from your original calculations.

The coupon on page 648 must be iattached to every query.

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BLUEPRINT SERVICEPRACTICAL WIRELESS

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, Is. each.

Dateof lessee. No. ofBlueprint

All -Wave Unipen (pentode) PW31A

Two -valve : Blueprints, le. each.Four -range Super Mag Two (D,

Pen) _ .. 11.8.34

Three -valve : Blueprints, ls. each.beectone Battery Three (I), 2 LF

(trans.)) .. -A -Sixty -Shilling Three (1), 2 LF

(R.C. & trans.)) .. 2.12.33Leader Three (SG, D, Power) .. -Summit Three (HF Pen, D, Pen) 18.8.34All -Pentode Three (HF Pen, D

(pen.), Pen) .. .. 22.9.34Hall -Mark Three (SG, D, Pow.) .. -Hall -Mark Cadet (D, LF Pen

(R.C.)) .. 16.3.35F. J. Camm's Silver Souvenir (HE

Pen, D (pen), Pen) (All -WaveThree) .. .. 13.4.35

Genet Midget (D, 2 LF (trans.)).. June '35Cameo Midget Three (D, 2 LF

(trans.)) .. 8.6.351936 Sonotone Three -Four (HF

Pen, IIF Pen, Westector,17.8.35

Battery All -Wave Three (D, 2 LE31.8.35

The Monitor (HF Pen, D, Pen) .. 8.2.36The Tutor Three (HF Pen, 1), Pen) 21.3.36The Centaur Three (SG, D, P)

Four -valve : Blueprints, ls. each.Fury Four (2 SG, D, Pen) ..Beta Universal Four (SG, D,

Cl. B) . 15.4.33Nucleon Class B Four (SG, D

(SG)F,

LF, 6.1.34Fury our Snper (SG, SG, p, Pen)Battery Hall -Mark 4 (HF Pen, I),

Push -Pull)

Mains Operated.Two-vsdvo : Blueprints, is. each.A.C. Twin (D (pen), Pen)..A.C.-D.C. Two (SG, Power) .. 7.10.33Selectone A.C. Radiogram Two

(D, Pow.) ..Three -valve : Blueprints, Is. each.Double -Diode -Triode Three (HE

Pen, D.O.T., Pen) ..D.C. Ace (SG, I), Pen) ..A.C. Three (SG, D, Pen)A.C. Leader (HF Pen, D, Power)D.C. Premier (HF Pen, D, Pen)Ubique (1IF Pen, D (Pen), Pen)..Armada Mains Three (HF Pen, I),

F. J. Camm's A.C. All -Wave SilverSouvenir Three (HF, Pen, D,Pen) ..

"All Wave" A.C. Three (D, 2LF(R.C.))

A.C. 1936 Sonotone (HF Pen, HFPen, Westector, Pen)

Four -valve : Blueprints, 1s. each.Al:. Fury Four (SG, SO, D, Pen)A.C. Fury Four Super (SG, SG, 1),

Pen).A.C.A.C. Hall -Mark (HiPen, D, Push -

Pull)Universal FcllMaili (HF, Pen, 5,

Push-pull) .. 9.2.35

10.6.3315.7.33

7.4.3131.3.3428.7.34

18.8.34

SUPERHETS.Battery Sets : Blueprints, ls. each.

Superhet (Three valve) ..F. J. Camm's 2 -valve Superlict

(two -valve) 13.7.35P. J. Cumin's £4 Superhet

Mains Sets : Blueprints, Is. each.A.C. £5 Superhet (three -Valve)D.C. £5 Superhet(three-salve) .. 1.12.34Universal £5 Superhet (three


het 4 .. 11.1.30

11.5.35

17.8.35

31.8.35

SHORT-WAVE SETS.Two -valve : Blueprints, 1s. each.Midget Short -Wave Two (D. Pen) 15.9.31

Three -valve : Blueprints, is. each.Experimenter's Short-wave Three

(SG, D, Power) ..The Prefect 3 (D, 2 LF, RC and

Trans.) 8.2.36

PW3013

le

PW34APW35PW37

PW39PW41

PW48

FW49PM2

PW51

PW53

PW55PW61PW62PW64

PW11

PW17

PW34BPW34C

PW4G

PW18PW31

PW1-9

PW23PW25PW29

PW35CPW35BPW36A

PW35

PW50

PW54,

PW5G

PW20

PW34D

PW45

1'W47

PW40

PW52PW58

PW 43PW42

PW44PW59

PW60

I'W38A

PW30A

PWG3


Portable (HF Pen, D, Pen) .. 16.5.36Four -valve : Blueprints, Is. each.Featherweight Portable Four (SG,

D, LF, Cl. B)MISCELLANEOUS.

S.W. Converter -Adapter (1 valve) - PW48AAMATEUR WIRELESS AND WIRELESS MAGAZINE

CRYSTAL SETS.Blueprints, ed. each.Four -station Crystal Set .. . AW4271934 Crystal Set) - AW444150 -mile Crystal Set .. - AW450

STRAIGHT SETS. Battery Operated.One -valve : Blueprints, Is. each.B.B.C. Special One-valver - AW387Twenty -station Loud -speaker


PW65

PW12

AW449

These blueprints are full size. Copies of appro-priate issues containing descriptions of these setscan in most cases be obtained as follows:-"Practical Wireless" at 4d., " Amatetir Wire-less " at 4d., " Practical Mechanics" at 71d., and" Wireless Magazine" at I/,3d., post paid. Indexletters " P.W." refer to Practical Wireless"sets, " P.M." to " Practical Mechanics" sets," A.W." refer to " Amateur Wireless" sets, and" W.M." to " Wireless Magazine" sets. Send(preferably) a postal order (stamps over sixpenceunacceptable) to "Practical and Amateur Wire-less ". Blueprint Dept., Geo. Newnes, Ltd., 8-11,


Mains Operated.Two -valve : Blueprints, in. each.Consoelectric Two (D, Pen) A.C.. 23.9.33Economy A.C. Two (D.Trans) A.C. -Unicorn A.C./D.C. Two (D, Pen) . Sept.'35Three -valve : Blueprints, 1s. each.Home -lover's New All -electric

Three (SG, D, Trans) A.C. -8.G. Three (SG, D, Pen) A.P. -A.C. Triodyne (SG, D, Pen) A.C. 19.8.33A.C. Pentaquester (HF Pen, D,

Pen) A.C. . .. 23.6.34Mantovani A.C. Three (HF Pen,D, Pen) A.0.......-£35 15s. 1936 A.C. Radiogram

(FIF, ), Pen) .. .. Jan. '36

AW403WM286WM394

AW383AW390AW399

AW439

WM371

WM401.

By Po s -rONWER SElvr

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August 29th, 1936

I REPLIES IN BRIEFThe following repltes to queries are given in

abbreviated form either because of non-compliancewith our rules, or because the point raised is not ofgeneral interest.

A. V. B. (S.E.19). We have no details of the coil,and connections are not standardised. We cannotassist you in this case.

R. R. (Enfield.) Take a course at one of the technicaltraining colleges, such as the Northern Polytechnic.They will coach you for the appropriate examination.

W. B. (Itexham). We do not publish any book onthe subject.

A. L. (High Wycombe). We have not published anycircuit or blueprint for a receiver of the type mentioned.

J. A. (Hebden Bridge). In view of the differentcharacteristics of the valves we do not recommend are -fitting with modern valves in this particular set.

F. E. B. (Politycleiflon). The Prefect S.W. Three isthe best we can recommend in your particular case.

H. W. M. (Wood Green). See the various reports inthis issue in the Guide to the Show section. There areseveral makers of the type of apparatus mentioned.

W. G. (Wigan). We could not recommend a receiverto go with your condenser. Perhaps one of the setsdescribed in this issue will prove of Interest to you.

F. 0. (Fartneolib). The blue glow generally indicatesthat the valve Is being over -run, either due to excessiveH.T. or lack of G.B. It would appear from your otherremarks t hat t he circuit is wrongly wired or is otherwise

faultyliN. A. W. (Redland). We have not described themethod of fitting A.V.C. to the set in question.

F. H. (Kenton). We have no service data of theapparatus in question and cannot suggest the reasonfor the wire. Can you not communicate with the firmfrom whom you obtained this device ?

P. H. (Llandudno). We have no blueprint of areceiver for the parts named by you. The Hall -MarkFour is the nearest, but theoutput Is Class A push-pull,not Class B or Q.P.P.

J. M. (Glasgow). A blueprint is available, but theissue In which t he set was described is now out of print.

A. S. V. (Stoke Pages). We have not designed a setof the type mentioned within recent times.

J. J. (Manwood). We have not yet examined theapparatus referred to, but we have given one or tworeaders' wrinkles in which a similar device was em-ployed. We shall go into the matter in a future issue.

B. T. (Bolton). The code has been fully described ina past issue and in our Short. Wave Handbook. It willno doubt be referred to again in a subsequent articlein our S.W. section. The choice of a meter must beleft to you as we are unable to make definite recom-mendations and comparisons between various makes.

G. E. T. (Hull). We have no blueprint of a portableof the type referred to.

D. E. H. (Smethwick). The aerial must be short andefficient and probably the damping of your presentsystem prevents the receiver from oscillating.

W. C. (Hull). The receiver should be constructedexactly as described and the rectifying valve shouldbe included.

A. E. S. (Barking). It should be quite possible tomake the substitution, but without a circuit diagramwe cannot say what alteration (if any) must be madeto the wiring.

W. F. (Leicester). No doubt we shall deal with thepoint as raised by you, under the B.L.D.L.C. sectionin a future issue.

J. S. B. B. (No address). The apparatus may beobtained from Electradix Radios, whose advertisementappears in this issue.

BOOK RECEIVED,-J

B.T.S. S. -W. Constructors' Manual

WI:ER two of this interesting journalshort-wave enthusiasts has just

been published by the British TelevisionSupplies, Ltd., Faraday House, 8-10,Charing Cross Road, London, W.C.2, atthreepence. It is a magazine speciallyproduced for short-wave enthusiasts, andcontains many interesting articles, in-cluding constructional details of the World -Wide Two (an all -wave S.G.3), How to CutOut Noise, Tuning for Shorts, Do's andDon'ts, Using Your Present Set for Short -Wave Reception, Building Your OwnShort -Wave Converter, The B.T.S. 5 -valveShort -Wave Superhet, and an article by theEditor Of PRACTICAL AND AMATEURWIRELESS entitled " The Truth AboutTelevision." A useful List of Short -WaveStations is also included. An interesting.little journal which every short-wave con-structor will want.


PRONE SUPPLY STORESLARGEST RADIO MAIL ORDER HOUSE IN EUROPE

SEND FOR OUR NEW ILLUSTRATED GIANT CATALOGUE AND VALVE LIST 4D'AMMAINS VALVES famous Europa 4v. A.C. types,

H.L., L., S.C., Var-Mu- B.G.,H.F. Pens., Vas -Mu -11.F. Pens. 1-, 3- and 4 -wattA.C. directly heated output Pentodes, Full -waverectifiers, 250v. 60 ma.; A.C./D.C. types, 20 volt;.18 amp, S.G.,Var.-Mu-S.G.,,H., ILL., Power, 4/6 each.Full -wave rectifiers 350v. 120 ma., and 500 v. 120 ma.25 watt indirectly heated pentodes.

o Frequency Changers. Octodes, lIentodes, 5/8 each.BATTERY VALVES. 2 volts, ELF., L.F., 2/3;Power, Super Power, 2/9 ; B.G. Var.-Mu.S.G., 4- or5 -pin Pentodes, H.F. Pens., V. -Mu -11.F. Pens., 5/ -Class B, 3/6.AMERICAN VALVES. Genuine American DUO-

TRON all types, Is. 6d. HYTRON super quality, 3 months'guarantee, all types, 5/6.New Metal Glass Valves, all types, 616.

PREMIER CHARGER KITSs (for A.C. mains)

Include Tapped MainsTransformer andWestinghouse

Rectifier.8 volts at .5 amp. 14/68 volts at 1 amp. 17/615 volts at 1 amp. 19/-15+15 volts at

1 amp. .. 37/615+15+15 volts

at 1 amp. .. 50/-8v. at 2 amp,. 29/6

Premier Mains TransformersScreened Primary. Wire -end Type.

250+250 or 300+300 v.60 ma. 4v. 1-2a ., 4v. 2-3a .,4v.3 -4a., all C.T.IL T.8 & 9, 4v. la.,4v.4a.,all C.T.H.T. 10, 4v. la., 4v.4a., all C.T.

8/6 EACH350+350 V. 120 Ma. 4v.1-2a., 4v. 2-3a., 4v. 3-4a.,all C.T. 10/6500+500 v. 150 ma., 4v.2-3a., 4v. 2-3a., 4v. 2-3a.,4v. 3-4a., al1C.T.1 916

Terminal Types, as illustrated, 1/6 extra.100 watt auto transformers ; 100-110 v. to 200-240v.10/- terminal type.Westinghouse H.T. 8 or 9 Rectifiers, 8/6 extra.11.T.10, 9/6 extra.

PREMIERSMOOTHING

CHOKES25 ma. 20 HY 2/940 ma. 30 HY 4/-60 ma. 40 HY 5/6

150 ma 40 HY 10/6Speaker ReplacementChokes, 2,500 ohms, 5/6

MOVING COIL METERS0-1 ma. 100ohms resist-ance. Dia-meter 21in.,18/6.Larger model,diameter 3in., 22/6.Flush mount-ing Bakelitecases B.E.S.A. first -grade accuracy.Multipliers for above, 1/- each,Westinghouse Rectifiers, 17/6.

MOVING IRON METERSAny range between 10 and 500 ma.Also 1.3 or 5 amps. Read A.C.

or D.C.Flush Bakelite ease,- 21in. diam.B.E.S.A. standard specification 89.

.5/9 EACH.

Premier Eliminator Hits (torA.C. amine) Comprise maim

Transformer, West-inghouse Rectifier,Choke, Condensersand Resistances.120 volts 20

milliamps.. 20/ -With Trickle

Charger .. 2,8/-150 volts 30

ma. and 4v.- - - 2-4a C.T. L.T. 25/ -With Trickle Charger . -31/6250v. 60 ma. with 4v. 301 -Class " B " Eliminator Kits 27/6

Diagrams supplied.

SPECIAL OFFERELIMINATOR KITS for A.C. mains. 120 V. 20 Ma., or 150v.25 m.a.,T10/ tapped S.G. del. and output. Complete Kit withlong-lifi valve rectifier (replacement costs only 2/-).

CALLERS TO -20 -22, HIGH STREET,

CLAPHAM, 13.W.4MAatelay 2381

ALL -WAVE 3 -VALVEKIT

PREMIER SHORT-WAVE KITfor 1 Valve Re-ceiver or Adaptor,complete withChassis, 3 Coils,15-170 metres,Condensers, Gir-

1 cuit and all parts.

VALVE n16GIVEN I ArFREE ! ! !

2 -Valve3 -Valve

S.W. Kit, complete with valves, 19/6.S.W.Kit, S.G., Det., Pen., complete with

valves, 40/-.

PREMIER SHORT-WAVE COILS13 - 26, 22-47,41 - 94, 76 - 170

metres,

1/9EACH.

Four- or six -pin fitting. Onhighest gradeplastic material.

Formers only, 1/- each.Special Set of Three 4 -pin Coils, 15-150 metres, 4/-.Premier 3 -band S.W. Coil; 11-25, 19-43, 38-86 metres.Simplifies S.W. receiver construction, suitable ally

type circuit, 2/-.

SHORT - WAVE CONDENSERS,super ceramic,S. L.F., .00016,.0001, 2/9 each;,double --spaced.000015, .000025,.00005, 3/- each.All brass withintegral slow-motion, .00015,tuning, 3/9;.00015, reaction,

2/9.

PREMIER

From 12-2,000 metres in 4 wavebands without coilchanging. Tuned S.G., Detector and Pentode.Complete with 2 -volt valves and moving -coil

to bnyL.S. Diagram supplied. Nothing else 601..

PREMIER BAND PASS KITB.G., DET. , PEN. 200-2,000 METRES

Complete set of parts for this splendid receiver, includes Valvesand Speaker.

Diagrams included free.

501-- 70/ -

WIRE ENDED RESISTANCES1 watt any value .. 6d. 8 watts any value .. 1/64 watts 5.v.att15/;ny

value"..2/-

25

BUZZERS

Bakelite Cased Type 1/ -Premier " Loud Tone " 2/6

SHORT-WAVEHE CHOKES

10-200 metres ..Screened ditto ..Screened chokes,

180-2000 metres

9d.1/6

1/6

ALL POST ORDERS TO--

JUBILEE WORKS,167, LOWER CLAPTON ROAD,

LONDON, E.5.'Phone AMHerst 4723

GRAMOPHONE MOTORS.Collars Groins milt,consisting of A.C. motor100-250 V. high qualitypick-up and volumecontrol, 45/-; Motoronly, 80/- ; .TiniversalModel, 190-250 v. A.C./D.C., with high qualitypick-up and volumecontrol, 67/6; Universal

Motor only, 49/8 ; Edison Bell double spring motor., includingturntable and all fittings, 15/-; Cosmoeord Grams unit, com-prising A.C. motor, pick-up and volume control (list 55/-), 35/9.

PREMIER " HIGH FIDELITY" P.A.AMPLIFIERS.

10 watt A.C. output 17/7/020 watt A.C. output .. £10/10/0

With Valves.Also supplied as Kits.

20 watt £8/8/010 watt 25/5/07 watt A.C./D.C. 24/4/03 watt A.C. 22/0/0

All with Valves.

TRANSVERSE CURRENTMICROPHONE

(Reiss Pattern).

High grade, large outputunit, having an, exceptionallyfine frequency response withlow Hiss Level. The Fre-quency Range being from45 to 7,500 Cycles, phis -orminus 2DB. Real depthshading, and brilliancy ofmusic, as well as clear, cleancut personality of speech.Microphone. 30/ -Transformer 5/ -Table stand 7/8

5,000 TELSEN RG4.L.P. TRANSFORMERS.

Latest typo

All brandnew andboxed(Listed12/6) - 2/9Lissen"Hypernik"Q.P.P. 8-ITransformer, d ,,) 3/6

SPEAKERS, MAGNA-VOX, Mains energised," 154 ", 7in. cone, 2,500ohms, 4 watts, 12/6." 154 " Magna, 5 watts,25/-. " 152", 9in.cone, 2,500 ohms, 17/6." 152 " Magna, 9in.cone, 2,500 ohms, 6watts, 37/6. MagnavoxP.M.'s " 264," 7in. cone,16/6. " 252," 9in.cone, 22/6. Goodmaus

P.M., 10/6. Cossor P.n., 13/6. Blue Spot, 22 P.M.,in cabinet, 25/,

CONDENSERS.Paper TypesDubilier ;

4mf. 500v. working 4/-- 4mr. 800v. working 6/-

2mf. 750v. working 3/-4nd. 1000v. working 10/84mf. 2000v. working 13/ -

Western Electric :4mf. 250v. working.. 2/-2rnf. 250v. working.. I/-1mi. 250v. working.. 6d.dint. 350v. 2/6ilant 350v. working.. 1/6

CONDENSER BLOCKS -All 250 volts working.

Dubilier2 +2 2/-2 +2+1+1+1ml. -. 2/6

4+1+1+1 +.54-.5+.5 mf. 1/6

4+4 4-1 4-1611... SI-Wego 1 mt. 450v. working, 1/700r. working, 2/-; 4mf., 3/6;2nif., 5/6.

ElectrolyticsT.C.C.

8nuf.650v.(surge)4/-4mf.650v.(surge) 4/-15mf. 50v. .. 1/-15mf. 100, .. 1/-50ruf. 12v. .. 1/

Dubilier:4ruf. 500v. .. 3/-8mf. 500v. ...8-4mL 500v. 4/-50mf. 50v. .. 1/912m1. 20v.25mt. 25v. ..

:

4, 8, or 12.mi. 530v.peak 1/9

8 + 4mf. 500v. peak 2/34 4.4mf. 500v. peak.. 1/68 -I-tmf. 500v. peak.. 2/612 4-8mf. 500v. peak . 2,612 + 4mf. 500v. peak 2/6

; 2mf., 1/9; 4mf., 3/-; 2mf.,lmf. 1650v. working, 316

Special Offer. Band -Pass Kit. 14/6 the lot. Lissen 3 -gangCoil unit. Utility 3 -gang condenser and Disc Drive, 4 valve -holders, Chassis 'and Blueprint. -

Lissen An -wave 2 -gang screened Coils with switching. 12-2,000metres, 12/6.

Potentiometers by well-known makers. All sires up to 1 meg.,2/-; with switch, 2/6.

CITY CALLERS TO165 & 165a, FLEET STREET,

E.C.4. Central 2833


Miscellaneous AdvertisementsAdvertisements are accepted for thesecolumns at the rate of 3d. per word. Wordsin black face and/or capitals are charged

' double this rate (minimum charge 3/- perparagraph). Display lines are charged at6/- per line. All advertisements must beprepaid. All communications should beaddressed to the Advertisement Manager," Practical and Amateur Wireless,"8, Southampton Street, Strand. London.



RADIOIVIART (G5111)SHORT-WAVE SPECIALISTS



electrolytics 8 mf. 500, 2/11, 4 x 4 mf., 1/6, 23 mf.,25 v., 1/-, etc.DADIOMART. Smoothing chokes, 20 by 120 ma.,'1N, 3/11 ; 100 ma., 2/11 ; 40 ma., 1/11. Telsen Acetransformers, 1/11. Radiogrands, RG48, 2/9. BTHspeaker. 2/11.

RADIOMART.Varley iron -cored, 10/6. Bifocal

dual -range coils. Very selective, 2/11 ; matchedpair, 5)3.

RDIOMART. Pushback wire 6 yds. 6d., heavyDa.; 2 gross solder tags, 6d. Resincored solder,

911.,RAD IOMART. Centrelab pots, all sizes, 1/6;

switched, 2/-. Tubular glass fuses, 2d.DAD' °MART. Igranic midget jacks, 3d. Milliam-IN meters, 25 ma. upwards, 5/9 ; super 6/9.

RAD1OMART. Telsen B.F. chokes, 1/11 ; screened1/11. Utility 1936 SL wavelength dials, 3/11.

ADIOMART. Lissen 3 -gang superhet kit coils,R two ganged condenser, ditto Bandpass,'ditto 2 gang all Wave, 10/- kit.

D'aTelltT0/0Traders'fo1

;monstera parcels.liari

parcels,

00 ADIOMART. Famous continental A.C. valves,.11 4/6. American Durtron, etc. All types, 3/6.Battery from 2/3.

AD1OMART. Utility 8/0, microdise dials, 3/11Radiophone .00010 short-wave condensers, 3/6

Series gap twin, 3/9.ADIOMART. Ceramic all brass microvarlables,

Tx 15 mmfd., 1/4. 40 mmfd., 1/7. 100 mmfd., 1/10.Short-wave RFC., 9d.no AD IOMART. Orders 5/- post free. Get our bar -IN gain catalogues. General, 10. Short-wave, 1)d.44, Holloway Road, Birmingham. Tel.: MID 3254.

'AL T'

goods previously advertised are standardlines, still available. Post card for list free.

VAUXHALL UTILITIES, 163a, Strand, W.C.2.Over Denny's the -Booksellers. Temple Bar

D338.

CONVERSION UNITS for operating D.C. Receiversfrom A.C. Mains, improved type, 120 watts

output, at £211010. Send for our comprehensive list ofspeakers, Resistances and other components.

WARD, 46, Farringdon Street, London, E.C.4.Telephone : Holborn 9703.

1937 RADIO AT THE WORLD'S LOWEST PRICES.6 -Valve All -wave Superhet A.C./D.C. 17/2,050 metres.National Union valves-Magnavox speaker-largeairplane Dial-all the newest improvements. (Nota Midget) -18 by 14 by 10. Never before offered atsuch a low price, £5/19/6. 8 -Valve A.C. Mains, all -wave super 4 Bands ; 11/2,050 metres: Highly sen-sitive-interference free-noise suppression and everyother refinement in 1937 Radio. £13/13/0. Compre-hensive guarantee, including valves. Absolute satis-faction or money refunded immediately. Goodscarriage Free.Radiographic, Ltd.. 68, Osborne Street, Glasgow, C.1.


W.C.1. Tel : Holborn 4631.

LOUDSPEAKER REPAIRSREPAIRS to Moving Coil Speakers, Cones and Coils

fitted or rewound. Fields altered. PricesQuoted including Eliminators, Loud -speakers Re-paired, 4/-. L.F. and Speech Transformers, 4/- postFree. Trade invited. Guaranteed. Satisfaction.Prompt Service. Estimates Free. L. S. Repair Ser-vice, 5, Balham Grove, London, S.W.12. Battersea1321.

SHORT. WAVES

211-B.T.C. SHORT-WAVE GUINEA KIT.Reviewed July 4th issue. Latest design

for CONVERTER - ADAPTOR ONE - VALVER,13/52 in. Mains or Battery. No Soldering. Excel-lent reception reports. Descriptive Leaflet .,1 stamp.Order your Guinea Kit to -day.

BENNETT TELEVISION CO., REDHILL.

AMAZING VALUEN.T.S.SCREENED, GRID 3

DIRECT FROMFACTORY TO

YOU.

and 18 monthlypayments of 71 -

Wonderful up-to-date 5.0.3Receiver that will give endless r5pleasure and receive a wide _12-6choice of British and Foreign Cash or C.O.D.programmes with excellentfidelity of tone and remarkable Carriage Paid.volume. Incorporates British long -life Screened Grid Valve forrange, detector and high -efficiency Pentode for power and low H.T.consumption. Metal Chassis, N.T.S. Matched Pentode Moving -Coil Speaker, Wave -wound Screened Coils. Full vision illuminatedWavelength Scale. Only 9 m/a H.T. consumption, Wave -range200-550 and 900-2.100 metres. Complete with valves, Oldham120 -volt KT., Oldham 2 -volt Plus 50 L.T. batteries and exquisiteWalnut veneered Cabinet (illustrated). With full aerial equipment.Overall dimensions : 18iins. high, 14ins. wide, 10ins. deep.Cash or C.O.D. Carriage Paid, £5 12s. 6d., or 5/- down and 18monthly payments of

READY TOPLAY.

POST THIS COUPON NOWFOR CATALOGUE OF FULL RANCE OF N.T.S. SETS

NEW TIMES SALES CO.ae (PR.W.I8), LUDGATE HILL, LONDON, E.C.4Dear Sirs,

Please forward Art Catalogue of your latest Battery andAll -mains receivers.

NAME

ADDRESS

PR.W.113.

AgainErie Resistors are specified by " Prac-tical Wireless "-used and specifiedby the designers of the " BandspreadS.W. Three " and The " Signet Two"in this issue. Erie Resistors are speci-ally impregnated to prevent breakdownand are unequalled for reliability.

ERIE ResistorsERIE

Volume ControlThe volume con-trol that will notdevelop faults.The Erie resist-ance element andprecision con-struction givesmooth contact,freedom fromhop -off noisesand durability.All sizes 5,000ohms to 2 meg-ohms, 3/6.With built-inmains switch,5/..

Colour Code Churl free front:

THE RADIORESISTOR CO., LTD.1, Golden Sq., London, W.1




POST PAID.PEAKEES.-cdestion Sonndex Permanent Magnet,

10/-; Telsen Permanent Magnet with ten -ratiotransformer, 12/6; Blue Spot 99P.M. ExtensionSpeaker, 20/-; 45P.M. Extension Speaker, 17/6;Telsen Loud Speaker Unit, 2/6; all new and boxed.


quisite Bakelite cabinet with Osram M.C. Speaker.Ready to plug in to any mains. Fully guaranteed.New, in sealed cartons, £3/5 (list £7/15).

G.E.C. Colpact 3 -valve Battery Sets complete with3 Osram valves, moving coil P.M. Speaker in

attractive Bakelite cabinet, makers' 1936 series inoriginal sealed carton, 50/- (List £5/10/0).


Speaker. Three Mullard Pentode valves in beautifulwalnut cabinet. Brand new, in sealed cartons, £4/10(List £8/8).

TELSEN A.C. D.C. MULTIMETERS (latest 1936type). -5 -range for every conceivable test for

radio and domestic electrical appliances, 8/ 6 each.OILS.-TELSEN (1936). Iroh-cored Coils, TypeC W349, midget size, 4/-; type W478 (twin), 9/ -

pair; type W477 (triple), 16/-; type W476 (triplesuperhet selector and oscillator), 16/- set. All GangedCoils are Mounted on Base with switch. I.F. Trans-former Cone W482, 5/-; Telsen Dual Range Coil withvariable series condenser W76, 4/-; Varley SquarePeak Coils BPS, 2/-.

ELIMINATORS.-Regentone (1936) Type. V5awith trickle charger, 37/0; Type WIa (less

trickle charger), 32/6.HOUSE TELEPHONES. A SPECIAL BARGAIN. '

BRAND NEW ONE -HAND TELEPHONES.Complete on stand, with or without Automatic Dials.Cost £4 each to manufacture, 10/ - each.

MICROPHONES.-Age(P.O.) Microphones, com-

plete with transformer, perfect with any typeof receiver, 4/6.

TRU-OHM RESISTANCES. -1 Watt. Wire endsI colour coded and marked ; 36 assorted capacitieson card, 6/-.

Mall VALVES.-A full range of valves forAall American sets at 7/- each. Brand new,guaranteed.SOUTHERN RADIO BRANCHES. -271/275. High

Road, Willesden Green, N.W.10 ; 46, Lisle Street,W.C.2. All mail orders to 323, Euston Rd., N.W.I.SOUTHERN RADIO, 323, Euston Rd., London,

N.W.1 (near Warren Street Tube). 'Phone:Mn seem 6324.RADIO and ENGINEERING SUPPLIES.TUBULAR Condensers, by well-known manufacturer,.002, .01, .02, .05, 0.1, 0.25, 4d. each.ERIE Resistors, 1 watt type, all values, 4d. each.SHORTWAVE Condensers, all brass, 10/1 vernier,with knob and pointer, .0001, .00015, 2/10, .0002,.00025, 3/6.ULTRA Shortwave Condensers, Stealan endplates,silver coated brass vanes, .000015 to .00016, 2/10.SHORTWAVE Straight vision drive, dual ratio, 8 to 1and 100 to 1, 4/10.CHOKES Shortwave H.F. low loss, 10-100 metres, 7d.VALVE Holders, clix chassis mounting, 4-5 pin, 3d. ;7 -pin, 4d.AMERICAN Valves, normal types, 4/6., all guaranteed.ELIMINATORS, Speakers, Kits, etc., write for lists.TRADE Enquiries, send stamp and trade heading forlatest lists.RADIO and ENGINEERING SUPPLIES, 88, EdgwareRd., London, W.2. Phone : Padd. 6052.


HULBERT for Quality Surplus Speakers. AllMusic Lovers should write for List of amazing

bargains. Prices Rom 8/6 brand new. Made by bestknown British maker.-Hulbert, 6, Conduit Street,W.1.

VALVES. By well-known manufacturer. Com-plete range of Battery, A.C. Mains, Rectiliees.

Brand new stock with six months' guarantee. 2 voltDetector, 2/3, Power 2/9, Screen Grid, Pentode. H.F.Pentode, 5/-. The following American type valves,fully guaranteed, at 5/6 each: No. 80, 42, 43, 57,58, 77, 78, 6C6, 6D6, 25F5, 2535. Write for otherprices to : Ddlci Electrical Co Ltd., 7, Lizard Street,London, E.C.1.

3S. EACH any popular type of American valves.90 days guarantee. Orders 10/- or over Carriage

Paid. Entire Satisfaction or Money Refunded imme-diately. RADIOGRAPHIC LIMITED, 66, OSBORNESTREET, GLASGOW, C.1.

MISCELLANEOUSQ HORT WAVE on a crystal set. Full buildingS

instruction and crystal, 1/2 post paid.-Radiomail,Tanworth-in-Arden, Warwickshire. _

FAMOUS Radio Correspondence Course for Sale.Cheap. Also experimenters surplus. Details,

Banham, 73, Shardeloes Road, S.E.14.

August -2h,. 1936 PRACTICAL AND AMATEUR WIRELESS III

BRANDNEW

Such amazhai value onlyPossible by supplying directto public. You will marvelat the difference in tone to yourset. Note these money.savingprices : - 2 - VOLT BATTERYTYPE, 11.2, H.L.2, L.P.2 1/9 each,Super Power P.2, 2/0 each, Screens andPentodes, 3/9 each. A.C. MAINS 4 -VOLT,I AMP. General Purpose 3/3 each, Power,4/- each, Screen and Pentodes, 4/6 each.FULL -WAVE REMMERS 3/6 each. Allvalves critically tested before despatch and sent Postfree. Cash with order or C.O.D. over 10/-. Send NOWNI CLARION RADIO VALVE CO.Dept. PW.5), Tyburn Road, Erdingten, 'v BIRMINGHAM.

2 cmFOR

An opportunity toparticipate in a special

offer, " Aircraft Cadet "Shock - proof Watch

with Handsome Chromeplated case, perfectly adjusted

Swiss Lever movement, fullytested for accuracy, with milanese

bracelet of stainless chromium -platedmaterial. 10 years' warranty. Send for

3d. deposit and 3d, part post. (6d. P.O. inall, no stamps) and 1/6 fortnightly until 17/6is paid. Cash Price 18/-. Ladies' Dainty model,

same price and terms. Also Superior Model Watch, un-breakable glass, cannot he overwound, 22/6, same terms.

AIRCRAFT PRODUCTS, LTD.(Dept. C.C.P.W.1.), 91, New Oxford Street,

London, W.C.1.

IDENTIFICATIONof amateur wireless trans-mitters can be found inthe RADIO AMATETJRCALLBOOK. This bookis essential to owners ofshort-wave, or all -wavesets. Contains completelists of amateur trans-mitters (with names andaddresses) from Alaska toZanzibar, also short-wavecommercial stations, listsof International Abbrevia-tions (the " Q " code);International Prefixes, etc.Price 6/- per copy, postfree. Send for lists ofother books dealing withamateur transmitting.

G5KA (Dept. PW), 41, Kinfauns Rd..Goodmayes, Ilford. Essex. I

EASY PAYMENTSDeposit

W.B. SENIOR .. 42/- 4/7W.B. JUNIOR .. 32/6 4/5BLUE SPOT SENIOR .. 29/6 4/-ROLA F.720 35/- 3/10

Any make of speaker supplied.GRAHAM FARISH SENSITY

SUPER 50i- 4/7 11 of 4/7GRAHAM-FARISH ALL

WAVE KITS .. 57.6 5/3 11 of 5/3SPECIAL.-G.E.C. universal mains A.C. or D.C. with M.C.Speaker, complete with valves in cabinet. List price, E6 10s.

Oar Price 78 deposit and 11 payments of 7/8.PARTS FOR ANY SET. ANY MAKE OF SPEAKER.

New goods obtained for every order.Send us a list of parts or valves you require or any speakeror set you stay select and we will forward you a definitequotation. Ten years' advertiser in the Wireless Press.

Thousands of satisfied customers.H. W. HOLMES,

New Address :-333, EUSTON ROAD, LONDON, N.W.1.'Phone : Museum 1414.

"THERE'S NO PLACE LIKE HOLMES."Monthly

Payments.9 of 4/77 of 4/57 of 4/19 of 3/10



BANKRUPTBargains. List free. Brand new

receivers to clear. GEC Battery Compact, 3v.with MC and BVA valves, 42/6. Alba 3v. with BVAvalves, MC and batteries, SG, 65/-. Ferguson 12v.AO/DC all -wave superhet., 14gns. Burgoyne 15gns.AC/DC radiogram, £8/1716. Cossor DC SG3v., 77/6.EKCO Car radio, 15gn. model, 12v., 7gns.' Ferguson,Pilot, Truphonic latest superhets, including all -wave,best part exchange offers. Midget receivers, 4v.with Mullard valves, AC/DC, very efficient, £3. Valves,Eur6pa AC and universal, most types, 3/6, also Radio -Record, TriOtron,, etc. All very keen 'prices. MostAmerieAn types. Dual coils from 1/4. Telsen RG4transformers, 2/6 ; Radiogrands, 2/-, Ace, 1/9. Others1/6. Telsen 2mfds:, 1/3. lrufds., 1/-. Electric irons,1/3. Household irons, 31b., 3/6. D.R. voltmeters,1/3. Cosmoehorde pickups with volume control,9/6 ; heads only, 4/-. Large stock of all the smallerparts. MC speakers, malty types, from 9/6. TelsenHI' binoc chokes, If, Screened, 2/8. Binoc chokes,9d. Record valves, 2v., 1/9 ; power, 2/6. Tricklechargers, 11/6. BCC 8mfd. electrolytics, 1/6. Follow-ing secondhand to clear : Ace 6v. superhet., shopsoiledonly, AC/DC, £5/10/0. Regentone AC eliminator,W5B with charger, 20/-. Elsco AC12, 14/-. AC25,16/6. Graham Farish Sanity AC.super with valvesand power pack, 32/6. SO battery 3v., with valves,8/6. Let me quote for all your radio requirements.Established 1929. Keenest prices. Phone Preston4030.-Butlin, 6, Stanford Avenue, Brighton.

MISCELLANEOUS

WE WILL MAKE A GENEROUS ALLOWANCE onyour old set or components in part exchange

for any new receiver or Peto-Scott kit.. Write forFREE EXPERT ADVICE before snaking your finalchoice. You are then assured of COMPLETE SATIS-FACTION. Prompt delivery of all the latest models.-R. Wigfleld, Furlong Road, Goldthorpe, Yorks.

HEADPHONES, Brown, G.E.C., Ericsson, Tele-funken, Sterling, etc. List free.

.RYSTAL SETS. Bursie-Jones. Complete. Guaran-teed,, 5/6. Ditto, double circuit, 8/-. Large

P.O. type, 10/-. Crystal detectors, complete parts, 1/-.Permanent detectors, 1/6.-Pos t Radio, 183, CaledonianRoad, London, N.1.

GRAMOPHONE attachments for Radio, electricmotors, 25s. ; Pick1ups, 9s. 6d. ; Portable

Gramophones, 12s. ; spring motors, 4s. 6d. ; walnutpedestal Anexagrans, £5 ; soundboxes, is. 6d. ; tone -arms, 2s. 6d. ; horns, 2s. 6d. ; cabinets, 4s. ; 1,000needles, ls. 6d.; gears, springs, accessories cheapest.Trade discount. Thousands to clear. Liquidatingstock bargains. Catalogue free.-Regentam, 120,Old Street, London, E.C.1.

ALL WAVE--RADIOON YOUR OWN RECEIVERConvert your existing receiver without alter-ation for operation on the short wave bands,bringing you America direct . .. programmes

from all over the world.UNIT SHORT WAVE CONVERTERNo other converter of itstype has these features -100 -1 tuning control, com-bined wave band andchange -over switch, range12 -SO metres, universalfor any A.C. or batteryreceiver, special outputmatching device ensuringcorrect matching NV.to any receiver. `"

Carr. pd.Send for new seas n's catalogue.

UNIT RADIO, 347, CITY RD., LONDON, E.C.1.

LIGHTNING 1POCKETVEST ) CALCULATOR%A 1936 MECHANICAL

MARVELFOR s. d. UP TO

L9,999/19/111DECIMALS --NUMERALS

UP TO 99,999,999Easily fits the pocket.Size 44in. a tin. a lin.EACH 5,9

ONLYPostage 3d.

Full instructions sent.Figures can be added,subtracted, multiplied

or divided with speed and accuracy.Write, call or telephoneMuseum 8331. State whether

L.s.d. or Decimal model required.SENT ON 7 DAYS' APPROVAL AGAINST REMIT-TANCE. Satisfaction guaranteed or money instantly -returned. ORDER NOW.

MARINE & OVERSEAS SERVICES, Ltd.(Dept. 31), 43, Woburn Place, LONDON, W.C.1.

ENGINEERINGOPPORTUNITIES

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NGINEERINGOPPORTUNITIES'

FREE!This unique Iland-book shows

the easy way to secureA.M.I.C.E.,A.M.I.E.E., A.M.I.A.E.,A.M.I.W.T. A.M.I.R.E., andsimilar qualifications.WE GUARANTEE -

NO PASS -NO FEE."Details are given of over 150

Liplonus Course, in all branchesof Civil, Mech., Elec., Motor,Aero, Radio and TelevisionEngineering, Building, Govern-ment Employment, etc.

IIwrite or this enlightening Hand -book to -day FREE and post free.British Institute of Engineering Technology,

409 Shakespeare House, 17, 18, 19, Stratford Place W.I.

ELECTRADIX BARGAINSMICRO AMMETERS for Valve Volt-meters, etc. New design of 2f" dia., panel -typemoving coil meter of extraordinary delicacy.Can read the signal strength on a midget crystalset even, and the price is only 40/-.DIXONEMETER for wide range testing Iliwork, 55/-. Set Analysers, with attachmentfor valve characteristics, reduced from fifteenguineas to £5.DIXMIPANTA.-A pocket multi -rangeuniversal meter at 19/6.DISC RECORDING GEAR and Tele-phones, Morse Keys, Recorders and Transmitters-Cheap.MIKES, Speakers and P.A. Amplifiers atBargain prices.PARCELS of experimental oddcoils, magnets, wire, chokes, condensers, switches, terminals, etc., postfree ; 10 lbs., 7/-; 7 lbs., 5/-.1,000 other Bargains in New Sale List 'N'


: Central 4611

FOYLESBooksellers to the World.

Special department for Wireless Books.119-125 CHARING CROSS RD., LONDON, W.C.2

Telephone: Gerrard 5660 (12 lines).

'FOREMOST AS PIONEERSOn Stand No. 77, at Radiolympia, you will findan interesting range of reliable wireless componentsmade by Varley. Will you pay us a visit ?

OLIVER PELL CONTROL, LTD., BLOOMFIELD ROAD, WOOLWICH, S.E.18

iv . '....TICAL AND 'AMATEUR WIRELESS August 29th, 1936

ri.IIESIINGNOUSES

WESTINGHOUSEMETAL

RECTIFIER

Style H.T.11. Output, 500volts 120 mA. Suitable forH.T. supply to receivers.

J.176 unit. Two J.176 units

in the voltage doubler circuitwill provide an output of3,000 volts 2 mA, suitablefor cathode-ray tubes. SmallerJ. and H. types may be usedfor grid bias supply.

5iaesed

beef2`s y:i

ufacteceivers

IggisWil zealelusive of fbe reoctV

13T°9 afaleffici ttgaibloteintrtss5fe.

of thletal

stbeittifeilsc:3sv:\t::Ptcl!tii:let;uive et -slice'fre s an "seose'c' ber

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":192:3;:it. atf:°05:1;n:LP13'

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larf, aorner

STAND 36, RADIOLYNIPIA

Westectors. Suitable fordetection and/or A.V.C.

WESTINGHOUSE

METAL RECTIFIERSWestinghouse Brake & Signal Co., Ltd.,82, York 'Road, King's Cross, London, N.1.

Published every Wednesday by GEORGE NEWNES, LIMITED, 8-11, Southampton Street, Strand, London, W:C.2, and Printed In Great Britain by THE NEWNESPEARSON PRINTING CO., LTD., Exmoor Street, London, W.10. Sole Agents for Australia and New Zealand : GORDON & GOTCE, LTD. South Africa : CENTRALNEWS AGENCY, LTD. Practical and Amateur Wireless can be sent to any part of the World, post free, for 17s. 8d. per annum; six months, 8s. 10d.Registered at the General Post Office as a newspaper and for the Canadian Magazine Post.

SOUND RECORDING FOR AMATEURS - World Radio History

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