Transistor Circuits Mai{Uai

No. f 68 216

TRANSISTOR

,'\ ) CIRCUITS MAI{UAI, { No. 4 by CLIVB SINCLAIR

C,lTTCLI'IS I!,\I] iiis] R,UCTXOiVS F]S}I BLIilLDING "frvo L tran.sistor supr:rilet. ). Ii!-Fi tape acri picii-up pre-arnp. l. lli-lji 3+irtt unrpli!iir- l. triiii;rture ma:.;\ D.:\,.cr packs. 5. 5 ficis to 2 mc/s sign:il injecfor. 6. Scnsitive subrtiniaiure lcudsgre:rker.racllo, 7" Single t;rrasistor reg;r_.ner*tivereceiver. . .i5-rrntf $, puirlic arirlrer;sanip!ifiei. -[ransirlor 9, voltmrrer. Ii.i" Sirnple earpiece r.eflex receir.er. ; i. Simp)i..transnritter.

BERNARDS RADIO MANUALS r

TRANSISTOR CIRCUITS MANUAL No. 4 by CLIVE SINCLAIR

LONDON

BERNARDS (publishers)LT.D BERNARDSRADrO MANUALS No. 168

GeNrn.,rr-Eorron : CLIVE SINCLAIR

First publishedDecember 1960 Repr.in,tedNovember, 1964 ReprintedJanuary, 1966 ReprintedMay, 1967

On Page II TAPE AND PICK-UP PRE..{N,PLIFIER In third paragraph of text, third line should read : 8 volts, not 2 volts.

On Page 12, Fig. 3 The 330K rcsistor betweenthe beseof Tr. I arrd the emitter of Tr_I should bc of pre_settype.

o 1e60.

Printed by V. Cooper parrners - & Ltd. Flitcroft Street, W.C.2. I'or Bernards(publishers) Ltd., The Grampians,western Gate, w.6.

l* '- l

CONTENTS

Page

Introduction 5

Noteson useof OCl69 transistor :'. 6

l. Two TransistorSuperhet.., 8 .

) I'Ii-Fi Tape and Pick-Up Pre-amplifier... 11

3. Hi-Fi 3-wattAmplifier 15

4, Miniature Mains PowerPacks ... l8

5. 5 Kc/s to 2 mc/s SignalInjector... 2L

6, SensitiveSubminiature Loudspeaker Radio 23

" 7. The " Mighty Atom SingleTransistor Receiver t{

8. l5-Watt Public AddressAmplifier 28

9. TransistorVoltmeter 29

10. Simple EarpieceReflex Receiver... 34

11. SimpleTransmitter 39

Addressesof Manufacturers 40 LIST OF ILLUSTRATIONS

Fig. No. Page

l. Physicaldetails of the OC169 .,. 7

2, Two TransistorSuperhet .,. 9

3, Pre"amplifierfor tapeor magreticpick-up 12

4. Responsecun'es for circuitin Fig. 3 13

5. Bassboost circuit lor Fig. 3 14

6. Circuitdiagran, of the 3-u,attamplifier 16

7. Miniaturemains pouer sr"rpplycircuits .,. 19

8. 5 Kcis to 2 nrclssignal injcctor ... 22

9. Circuitfor 3 transistorreceiver ... 24

10. " Mighty Atom " transistorreceiver 26

11. Additionof longwave coil to I'ig. l0 ... 27

12. First 3 stagesof publicaddress amplifier 30

13. Driverand outputstages.,. 31

14. High input resistancevoltmeter ,.. 32

15. Simpleearpiece reflex receiver .,. 36

16. I-ayout for simplereflex receiver... 37

17. Simpletransmitter circuit... 38 INTRODUCTION The , rapidity with which new componentshave appearedon lhe nome constructor-marketin recent months has betn pleasantlv surprising. It seemsthat,manufacturers are UeginningiJ i;i;'; new interest in this outlet for their products. - In the field of transistorsa new drift type hasbeen made available, the OCl69. This unit has the samepara-eters as the OCl70 bui ry]19.fo1 only l8/0d. which makes if far less of a luxury articf.. As rrs cnaracterutlcs are ertremely good it may be used in a great many a_pplicationsthat might suip-risesomeone unfamiliar iii'h them. Many of ,thecircuits in thij book make use of the OCl69 and a chapter o! the transistor itself is also included for those of )ou who hke to know exactlyrvhat sort of animal you are deating with. some of it is rather technical but a rittle uri"fttr..w o*i no one any harm. ., I have.bee.nreceiving a great many letters recentlyconcernine rne clrcurtsthat have appearedin the transistorcircuits manualsl-ind Many of them contain some query about one of tire clriuits llre.se.I3p .only.to-o pleased to-aniwer althoughsometimes I g;; ; Iittle behindwith them. However,I shouldliie to hearfrom irori of you concerningthe type of equipmentyori are most ilile;i;a;; so perhapsyou could sendme a postcard. . From the letters I have so jt lTj*:d far appears thaf receivers are the ,"o.i-;;p;ia; proJects(to borrow an excellent Americanism) and thi imall-f-[i, pocket sets^wjth.loudspeakerare the -ort poprilu. .f att. nas oeenreflected ln thls tssueand new setsare beingdesigned and tested at the moment. However, there may be othei ttp6 ;a;;i; which have not yet appearedbul which w6uld be welio^med. Transistors continue to replace valves in their traditional applicationsand the next take oler bid is likely to take placei,r the high fidelity field. power transistors are now available with performanceswhich are in no.way inferior to those ;a;;;".;bG valvesand thesemake it possibre-todesign quaiity "-piriii,i, *rtrt outpujs in_theregion of 20 watts. As a stirt iri this fieldihis manuil contains the circuit for a pre-amqiifier of extre;"t high F;i;;- ance and equipmentfor .usewiih this will appeir iri the future manuals-- whilst many still tend to think of th'e'transistorin terms ot portableusage it, has, in fact, many propertieswhich make it prercrabre to the valve in I?ICJI typesof domestiqequipment. ln tape recorders and other Hi-Fi equipment, where ttre 6rimination of mainshum is.of paramountimportince, tireii largescale adoption may not be far in the future. 'inaustsron. 6 C;ecurrs Maxr_lar,No, 4 In the books we have^publishedand in the n.ragazines,many cjrcrrits. have- -appear"a transistor ,.c"iu.., which simplicrt., {qa cornbine and low costrpith sufficientlytrign ferform"";; i;;iir;;; i ntcn,.l:ci .pplication. yuny superhefciriuit! n"u"- . jnto'th" ufio-;;il;i but ttrcschave never fallen ;G;;;i'ih; ;il j"iffi;;: tioned as they have used,.virtually withoiri 6xception,O, 8 transisiors. t;;;;;; This may have grvin ttri iverage fro* *nrti*toi-"*ir*o-ri"rv the erroneous idea that ar t-ransisioi r"pJi"t, c,ompricaicd,. iil expensive.anddifficult to uiiio. r.'iir'iii,i-tr*"."i.rr" theory this book contains -superhit "ii."itt'o-r ."riti".i"v lrp]i.itv which are suitabre?";ih"* ;^hl i'uu" buirt T.R.F. r.covered their first from their nrst itriitt ui-i,"a.ing it;;;i, ;;; dccidedri;at they require,ory.tt ing mo.J poi."t. the OC The arrivalof In,.)has made,v tur[ i.iufi";j;';;;i" in designing se^tsfor i;:, these colossalgain at tl.W. iriqGn.i.r-r.0.r".,' ti; "-G;;; of-siagrsrcquired foi any ei* p.if;;i;... By thc u'ay, . I am alwayiintereit"o n rr"u.inghow the circuitsin thesebooks are buirt andhow *.rr-'t"v r*it itiuu.iouipuii.itr,"^ countr),..Ma-ny.of you, I.know, thi;k up new- ways bf buildine ",d mod i tyi ng t he cqu i p.meni : l: ll i'*hi' describe'd. Sh"ii r,i v.""' U".ii,l""? tnese not write to,me giving_details p.*ipr, photograph "nitt.r'itiri,lr'v"uand ln.f"j,.;; or circuitciagrim. rrve the l.oncion or work in area ]'ou coitC cattln^i;;h ii ^y'ofn." which is in The Grampiansbuildiris -bein Streptreris ft";e. Should you have anythingrhat can usecl'inon" of tfr.iJGanuals you will, of coursc,be paid for it. NOTI]S ON THE USE OF THE OC169 TRANSISTOR The introduction of at a price, which l:ygtlt'ol rhat .the^OCl69 at 1g/0d is of eventLe^gg+s; ;ari, it Lrii6r" td;"1;;i!;;; OC45's,OC,44's or OCl70'snavlUii" ur.Jt.io.". The ocl69 is madebvrhe,attov oinuiion-tt'Lnique which achieves resultsfer superiorto ihe best'p;;;i6i; ;ri;; normatgermanium alloy.rnethoddby whichmeans rhe OC45and'OC4+;"-;;il;;il: Thc i ncreii ble i mDrove ment I " . rfoi,na,i."-u"ti"u.O' the oSJ69 f ;n;;;t"; may be reatised*ti*-;;;-;;;siders that its atoha cut-offfrcquencv is 100mc/s o. -o.". .o-piilO-rciJls jS for.rhe *itf,'"i,lv'dioii. ,i'ii,,o oC44 and thar irs po-wergain at ?50 'ifr"il" unila-teralisedcircuit compaiedwitfr ii ob. *it, is l'000,@0 tiribc+i timesas comparedwit-tr-5,000- td".. when usedas a mediumwave band frequenq,clqler ii--ufi piouit";;;: version.gainof 40 dB. comparedwith fri zd an OC44. os. "ut"i"iur" r-- Thehigh , frequencycJrt-offmakestheocl69 -it- ideal for usein F.M. recerverI.F. stageswhich,pormaJly operate Irequency to.l ,*lr.- ,,ii iirii eachstage will p,rovidei gain of ZS aS.--A;;#; appiicationthat is l-iketyto-^be reattv p-oputa'iiJin receivers raAio;;;i;;i operaringin ine zl mc/iuaiol-li hri, riiqid"y ;,h'; TnaNslstoR Ctncutrs ll{am;.lr- No {

ALL DIMENS|ONS iN mm. L-9'l .r INTERLEAD SHIELD 'nox' | I AI.iD METAL CASE -c I r-rl mA I l',' \.il/ zsto o'-j*l |..-l zs*o os-l l-- | ffi-l s O +0'15-+1 l.- -!1.-o ou

FIG. I. PHYSICAL DETAILS OF THE OC 169.

OCl69 operatesexcellentll', particularly in superretcn- circuits.. The O-C169u'ill, in fact,-replaccthe N1ullardOC170 or the Edisrr,anXA131 in any circuit and may be usedin superregen' circuitsat frequenciesup tc about 90 mc/s' If you wish-to incorporatetl-ris transistor in circuitsof your orvn desigirhcrc are tirc lirriting val':rcsr"'hich lrust not be exceeded:- -VCB 20V. -lc 10mA' Ic 10mA' -Ic lmA. Pc (Tamb =-45'C) 50mW. The averagevalue cf common emiiter current gain-is,100. The charatteristics at an ambient temperaturc of 25oC are as follori's:- Normal \lininrum Maximum -ICBC (-VCB .- 6V) : l'5microamps <13 -lC -- _vLrJlIE,,.o ,f 50mu.A\ ._ ."..g0\/. --,20\r. __0 J I -rp sn,n,rA\ -vEB - _ 0.5\. 1 rc'" u" ) -r'cs ' 1 --rD I av - 15mu.A' '<50 1 le -. lmA | -\'cB , 1 -\'BE,,^- f 6v : 260n.r\/' >210nrv'<330mv' t;''" : iJ,,li r -vcB . 6\- I F* I lc Im.A,! - tsoe. <'lodll. l-f ' - lKcis] TRaxsrsronCrncurrs Ml^-utt No. 4

* Spot r.roisefigure measured rvith an input source irnpedance o[ 500 ohms. The input source impedance at 450 Kc/s and 10.7 mc/s is 200 ohms and 150 ohms respectivelylvhen VCE : -6V antl IE : lmA. At broadcast band frequencies and at shortu'ave frequencics t-rir to 10 mc/s the pcrformance of drift transistors is particularly gootl because, unlike alloy junction transistors, their current gain does not begin to drop until 10 mc/s is reached. At all frequencies, liowever, the current gain is dependent upon the emittef current and is ten times as high at 2 mA. as it is at 300 micro. amps. The current gain does not vary noticeably with the collector voltagc. howevcr, so that choice of this operating point is normally governeil by variation in the other parameters such as the inter-electrodc capacitancesand thc input and output impedanccsmost of which vary fairly considerably'. A typical operating conditior.ris I mA. collcctor current and 6 volt collector-emittervoltage rvhich pror,idcs a. close approxin-rationto optimurn gtlrl conditions. In slrecial circuits such as those to rvhich A.G.C. is to be applied, the collector currcnt may beconsiderably less and is typicallyonly 100micro. amps in the first I.F. stageof transistorreceivers. As thc output impedance of drilt transistors is considerablv highcr than that of normal junction types, LF. transfornrersrritlr tappcd primaries arc not usually required. The OC 169has for-rrlead out wires in place of the usual three. the cxtra lead bcing an internal shield intcrnally connectedto the case of thc transistor.

T\\'O TRANSISTOR SUPERHET Tire avernge transistorsuperltet on the market uscssix transistor.s in a circuit rvhich l'aries vcry littlc front one nranufircturer trr anothcr. The first stage is usually an autodyne converter, which combincs the functions of local oscillator,mixer and I.F. aniplifier-, the second and tirird arc I.F. antplifiers and the rcnraining trvcr stagesprovide thc nccessaryA.F. gain, the last stage using t\\'() transistors in a push-pull circuit to drive the speaker. Whe,r loudspeakcroperation is not requiredthe linal stagecan be dispensed rviih and the driver used to drive an carpiece. This rcsults in thc saving of t\\,o transistors. Using two OCl69's for the first twrr stagcsmakcs the secondLF. transistor unnecessarybccause of thc cxtra gair.rplovidcd. Finall1.,the A.F. Dril'e r may bc eliminated b.,' reflexing the l.F. siege to fulfill this function. Our original six transistorshavc norv been rvhittled dorvn to oniv two rvithout loss of pcrfornrancc. Scnsiriritl and sclecrivityremain vcry much thc same thc only differcncebcing that thc set rlow dril'cs an earpiecc instead of a spelkcr. The advantagcsof this type of set over the less expensivere- generativc detector type of receir,er are it's superior quality, Tnausrsron Crncurts Mexulr No. 4 10 TzurNsrsroRCrRcurrs lvlauuni No. 4 sensitivityand easeof operation. Whilst the regen.can often give excellent resuits it has insulficient R.F. gain for really tricky areas and in these areas a superhetsuch as this one should operate perfectlywell. The completecircuit diagram fcr the receiveris iliustrateCin Fig. 2. Trl is an autodyne frequencychanger using an OC169 which providesa conversiongain of about 40 dB throughout the broadcastba;rd. The LF. signaiis sclectedby I.F.T.I. which feeds it to the secondtransistor. Tr2 servesboth as I.F. amolifierand asthe A.F. stage. Detectionis by meansof an OA70point contact diodewhich alsosupplies the A.G.C. voltagefor Tr2. This A.G.C. is sufficientlystrong to keep the signallevel from overloadingthe stageon largesignals. To avoid the useofa largetuning capacitor,the rcceiveris tuned by meansof trimmers. Four trimmersare used, each having a value of 100 pf. As there are two circuits to bc tuned the number of programmesthat may be received,without adjustmentbeing made to the set, is limited to twc. As most people rvill only wish tc receivethe l{on're and Light prograrnmesmost of the time, this may not be a very severcdisadvantage. If a third stationis likely to be requiredfrequently, how,ever, a further pair of trimmersmay be added. Adjustment ol the receivcris fairly simple becausenc serious alignment-problems arise. Connect an aerial to the top of the. primary of Ll via a 10 pf capacitor. Now, with switchesSl and 52 open, adjustC2 and C5 to receivethe stationyou require*,ith the higher frequcncy. Adjust IFT1 and IFT2 in turn to cbtain maximum volume and then readjust C2 and C5 ii necossary. Sl and 52 may now be closedand C1 and C6 adjustedfor reception of the iorvcr frequencystation. The aerial may now bc removed anC minor adjustmelts nrade to the four trimmers to ensurc rnaximumsensitivitJ-. Shouldyou find the sensitivityof the receiverinsu{ilcent in your areait may be increasedby applyingregeneration to fi2. As ihis transistoralways amplifies at thesame frequency no adjustmentneed be rnadeto the setti:rgof the regene;ationcontrol whon switching from one station to tne other. The sirnplestway of applyingthe required positive feedback is to conncct a 15 pf. beehivetrimmer betweenpin 4 of IFT2 and pin 1 of IFTI adjustrnentbeing made for nraximumgain short of oscillation The rcccivcr uses only a 3 volt battery for it\ power supply and this will aid the constructor who wishes to bulld a reallv compact set. The smallest3 volt battery on the market is the Ever Ready D22 which may be orderedthrough Boots the Chemists and which is only lf" long by 3" in diameter. As the current consumptionof the setis only 1ma.even this tiny batterywill give a reasonablelife ll Tn.q.xstsron Cncutis M,lNu.qL No. 4 tl

Components List for two transistor superhet R1 10K ohms R2 2.7I{ ohnrs ii.3 I K oirnt R.4 2CK ohns R5 5 K ol,ms variable rvith singlepole switcil C1,C2,C5,C6 Ail 103 pf. trimmers, postagestamp type C3,C4,C8 All 0.0i nu.l. Lt 0.05 nru.f. Trl,Tr2 OCl69 diode ti'pe OA70 or similar E 250 ohm ci.c.earpicce such as Ardente ER'::C Batiery 3V Ever Readytype D2,1or larg.:rtype

TAPE AND PICK-UP PRTI.AMPLIFIER This pre-amplifier was designed.by the General Electric Ccmpatty for use either with a tape recorder or rvith a magnetic gramcplione pick-up, giving NARTB correction in tl-recase ol the forn;cr and RIAA compensationto the lattcr. The total harmonic distoriicn of the prc-amp. is lessthan Iii. The pre-amp is suitable for virtua-ll5,anf impedance magnel-ic pick-up because thc input ia-rperlance of the an.rplifier u'irl be generally highcr than thai of the plck-up. Variations in the impedance of the pick-up due to changesin frequencrvwiil, th,:leforc, be unimportant. The first two stages are stabilised against temperature ch::ngcs resistor shoulC l;e of up to 40" C by current feedback via Ir.2. This - ' varied until the collector voitage of Tr2 is,/volts. The voltage feedback fron the collecior of Tr2 Cecrcases3l lor,v frequencies because of the increasing reactance of the fe;r,llrack capacitor in series rvith the treble control. This is done to ll:Lieve irequency selectivecompensation for the standard NARTB rc;ortl- ing characteristic for tape or the standard RIAA for gramoihotre reiords. The level responsefrom a standard NARTB pre-re;,.rriied tape occurs with the treble control (Rl2) at mid positicn cr 12 K ohms (seeFig. 4). The output stage, formed by Tr3, is an emitter follogei' or common collector amplifier and has, therefore, a very low output impedance which rnakes it suitable for feeding into virtually any length of cable to drive a tiansisior or valve power amplifler. In'rNstston CrnCUrtS MAN'Lr.A,LNo. 4

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IJI U J TnaNsrsron Cncurrs M.lNu,cl No. 4 15 For optimum operation the treble control should have a linear track and the volume control or level control an audio or semi-log track. For the power supply two PP3 batteries may be used ii seriesto giveextremely long life as the currentconsumption is only 3.5ma. If the pre-amp, is required for use with a tape deck operating aj 3 al1p.s., R I 2 shouldbe setat 25 K ohms,the feedbackcipacitoi shouldbe raisedfrom 0.01mf. to 0.02mf. and the 47 ohm iesistor from the emitterof Trl to groundshould be shuntedrvith a 0.5 mf. capacitorto obtain a flat responsebeyond 10 Kc/s. ComponentsIist for pre-amplifier Resistors:- 15K,47ohm, 1.5K >:2,72K,8.2K-all.|wattfixed. 500K, 25K, SK-variable. Capacitors:- 20mL x 2-20Y.W., l00mf. l0V.W., 10mf. l5V.W., 0.01mf.x 2, 0.03mf. Transistors:- Trl 2N508 Tr2 2N508 A suitableequivalent for anv of Tr3 2N322 theseis thi Mullard OC45. One of the many p-roblemsassociated rvith home listening is the need for opcration of the Hi-Fi equipment at a lower sound level than would be found in a normal concert hall. The troublc arises becausethe humanear is far from linearin it's responseto differeht fr^equencies-and-this_responsevaries considerably witn the intensity of thesound. The Fletcher-Munsencurves showihat asthe intensiti of the sound.isreduced the basefrequencies have to be boostedto maintain.the same subjectivelistening level. This boost is fairly considerableand antounts to about 10 dB. per octave beiow 3OOc/s when the overall listeninglevel drops 40 dB. To achieve this bassboost in the pre-amp.just describedthe circuit shown in Fig. 5. may be addedto the output. For the 0.7 Henry choke the primary of an Ardentetransformer type D122 is suitable. CornponentsList for BassBoost Circuit 50 K ohm linear potentiometerfor basscontrol. !1 Henry choke.approx- 50 ohm d.c. (Primary of Dl?-2Ardente). 10 mf. electrolyticl5 V.W.

3 \\ATT HI-FI AMPLIFIER In Transistor Circuits-Manual No. 2, I describeda high per- formanceone watt amplifierdesigned by G.E.C. From the iuniber of letters and telephonccalls I receivedconcerning this circuit it evidentlyproved very populai but many readersasked for an amplifier.tvith higher output po\1'er. Well. G.E.C. have once againproduced an excellentdesign, this time for an amplifierwith a clear 3 watts output, and have evenimproved on the frequency responseand other characteristicsof their smallerunit. r-

16 TneNsrsron Cncurrs Merurr" No. 4 t----l r l> lal-- | |--{[ r I I I I o ll \\ tl \e7 ,-r

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lf the amplifier is used u'ith the pre-amplifierof Fig-. 3., the first transistor,Trl, may be omitted and the output from the 'Dre-amp. connected to thebase ol T12' To avoid the use of an output transformer,which would be ratherbulky becauseof thelorv d.c. resistance that rvouldbe required, a singleended output stageis used,direc-tly coupled to the loud- speakerwhich shouldhave a voicecoil ol from 3 to 5 ohms. The output transistorsare in seriesacross the power supply so that eachbperates from only 6 volts. Forward bias of between 2 and 5 ma. is applied by meansof Rl2 and Rl3 to preventcross- over distortion.--6 dB of negativefeedback at 400c/sis applied from the loudspeakerto the base of the driver. The output transistorsare GETll5's mountedon 3" )i 3" fins to act as heat sinks. The driver transistor,a GETl16, operatesas a ciassA amplifier dissipating320mW. rvith a coliectorcurrent of 35mA. Coupling to the output stageis by meansof a 3 : 1 * I phasesplitting transformer rvhich may be cither a Colne Electric 05009or a Parmeko P2943(see components list). Becauseof the high current level at which this stage operatesthe input and output impedancesare vcry lcr*',making it neccssaryto usea 250 mu.f. elcctrolyticfor de- coupling in the emitter. A lower value than this should not be used as it would reduce the low frequency gain by providing frequencyselective negative feedback. The pre-amplifierstage, rvi-tich, as mentioned above, may be onritted,uses a GETl16 biasedto a collectorcurrent of 2.5mA. The un-bypassedemitter resistorgives rise to a small amount of negativefcedback and increasesthe input impedanceto about 5K ohms, thus providing a suitableload for the seconddetector of a conventionaltransistor broadcast receiver. The performancefigures given for this amplifier by G.E.C. are as follows:- Input resistanceof pre-ampiifierat 400 cis 5K ohms Input voltageto pre-amplifierfor 3 W output 150mV. Inbut resistanceof driver at 400 c/s 75 ohms lnput voltage to driver for 3 W output 80 mV. Porver gain with preamplificr stage 58 dB. Porver gain without preamplifier stage 45 dB. Total quiescent current at 2O"C 65 mA. Total current at 3 W output 400 mA. Peak power dissipationof eachoutput transistor 800mW. Frcquencyresponse 20 c/s to 30 Kc/s + 1+ dB' Total harmonicdistortior.r at 400c/s, 3 W output iessthan 5 /" As no output transformeris usedproblems of componentlayout do not arise, there being no componentsto interact. With the transistorsspecified, stable operation is possibleup to a tem' peratureof 55'C assumingnormal use on speechand music. r

18 TntNsrsron Crncurrs lr{,cxuA,r.No. 4 ComponentsList Resistorsall I watt l0l unless otherwisestated. Capacitors RI 5K ohm log.- variable Cl Smu.f.12V.W. R2 22K ohm C2 8mu.f. 6V.W. R3 15K ohm C3 50mu.f.6V.W. R4 1.5Kohm C4 8inu.f.9V.W R5 100ohm C5 250mu.f.6V.W. R6 1.5Kohm Transistors(G.E.C.) R7 2.2K ohm Trl GETll4 R8 lK ohm Tr2 GET1l6 R.9 150ohm Tr3 GET115l RlO 82 ohm Tr4 GETI15 f matcned Rli 4.7Kohm npeaker Rl2 270 ohm5li. Voice coil 3 to 5 ohms Rl3 270ohm 5li Rl4 0.5ohm R15 0.5ohm TRA},ISFORMER The transformershould have.thelowest possible d.c. consistent -b-r, resistance with a high pri-maryinductanci. over at transients ligh frcquenciesa--re iecuced ii uizuarseconiu.i.. u.. ur.o."--^"" . The transformerin the prototype fraOitre ioff.*i"g istics:- cjratcte._ Turnsratio 3:1 + I Primary induciance 1.1Henries Primary resistance lg ohms ^ .. Secondaryresistance g.5ohms each half JulraDlecommcrcial t]'pes are ColneElectric Limited 05009* -. -ParmekoLimited p.2943* * Bifilar windings.

MINIATURE NL{INS PO_\!ER SUPPLIES FOR TRANSISTOR EQIJTPMENT Experimentors who usetransistor an. otherlolv powereq'ipment often find-it infuriating to have t. ur. uiii"ii."r uir1i,"'tifr""'ci"J neverreally knows wh-etheror not " p"iti.i,G.Lattery is freshand "xact voltage.one requiris is iiiifv on srm.ple^.,T_p^f_tl:power hand. These supply circuits are designedto ovircome this problem and, in addition, may be permanentf installedinto radiosor other equipmentwhich u'ould no.miiiy r.iuii.luti.ri"r. -,: ! Tn,rNsrsron .Crncurrs MANUAL No. 4 19 i

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+ 25.)1. Voltoge Output. Doublcr Circuit

Voltogq Triplcr Circuit.

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Quodruplsr Cifcuit

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FIG. 7 MINIATURE MAINS POWER SUPPLY CIRCUITS r-

20 TncNsrsroRCrncurrs Ma,Nuar No. 4

To keep the cost of the units low a standard6.3V heatertrans- former has beenused in every caseand the diodes are the ordinary germaniumpoint contact t1'peswhich can often be bought from surplusstores for as little as a shilling. Despitethe facithat the output voltageof the translormeris always6.3, the output from the powe.rpaclmay. be anything from 6.3 to 35V dependingon the circuitconfllrration used and the load on the circuit. The amount of current that can be drawn from the circuit is limited by the max. permissibleforward current of the diode used. this.figure be-ingobtainable from the manufacturersspecification- In thc caseof the Mullard OA70 and OASl the maximumforward current is 50 mA. which is more than sufficientfor the averaqe transistorcircuit. Usuallythe current required will beless than 5mL. The choiceof transformeris completelynon-critical. Any type or nrake will be able to handle the power concernedanO it il,itt usuallybe convenientto selectthe smallestsize available. _.The circuit diggramsfor the power supply circuits are given in Fig. 7. Five different circuits are shown the choice of ihe one most suitedto the constructorsrequirements being mainly a matter. of_thc,voltage desired in relation to the currentconsumpiion. The table below was compiledfrom measurementsmade usine OAgl diodcs. The GEX44 diodegives similar results. Circuit Current Drav'n VoltageOutput Half rvaveand Bridge 0mA. 8.5 Half rvaveand Bridge lmA. j.5 Half waveand Bridge 2mA. 7.0 Half waveand Bridge 3mA. 7.O Hall rvaveand Bridge 4mA. 6.8 Half rvaveand Bridge 5mA. 6.5 Voltagedoubler OmA. 17.5 Voltagedoubler lmA. 16 Voltagedoubler 2mA. 15 Voltagedoubler 3mA. 14.5 Voltagedoubler 4mA. 14 Voltagedoubler 5mA. 13.5 Voitagetripler 0mA. 27 Voltagetripler 1mA. 22.5 Voltagetripler 2mA. 20 Voltagetripler 3mA. 1.7.5 Voltagetripler 4mA. 15 Voltagetripler 5mA. 13 Voltagequadrupler 0mA. 35 Voltagequadrupler 1mA. 30 Voltagequadrupler 2mA. 26 Voltagequadrupler 3mA. 22 Voltagequadrupler 4mA. . Ig Voltagequadrupler 5mA. L4 -}

TneNsrsron Cncurrs MlNuer. No. 4 2l

Many types of diode, other than the point contact germanium types used here, may be usedto advantagein this type of circuitry- Siiicon junction diodes, when available,bre ideal becauseof their high power handling capacity and small size' The output yo]!ag-e foi a-given current will vary considerablywith the type of diode used and care should be taken to ensure that the voltage is never higher than the transistorsin the equipment can withstand. The values given for the electrolytic smoothing caPacitors-are not particularly critical but be careful not to exceedthe working voltageof the type used.

5,000 c/s TO 2 mc/s SIGNAL INJECTOR This little device is one of the most valuable assetsa service engineer-may or home constructor can have for tes-tingo1 {aul! tracing. It be usedfor R.F., LF. or A.F. equipmer,rtand is, therefore, ideal for testingradio sets. As a high voltageis not producedthe unit cannotharm transistorisedequipment. The circuit diagram of the signal injector is shown in Fig' 8. This type of circuit is known as a multivibrator and.it operatesas followi:- When the unit is switchedon both transistorsconduct a relativelyhigh level of current, about 6mA., this causesa sharp drop in collecior voltageand a positivegoing pulseis sent to-the other transistor which counteractsthe effect of the base bias resistor and switchesthe transistor off. This causesa negative going pulse which switchesthe first transistor on again. The 6utput waveform should, in theory, be a s-qqa-rewave but in practice^ it will resemblethe curve on the left hand sideof Fig. 8' becauseof delayed collector conductivitY. As the voltage rises very steeply to its maximum level, the output is very iich in harmonics of the fundamental frequency and as theseextend throughout the broadcastband the oscillator may be usedup to about 2 mc/s. The fundamental frequency of the multivibrator is determined by the products Cl >< R4 and C2 x R3 which should be equal' o.i, The frequencywill be approximately equal to - - CI R4 The frequency rvill be slightly reduced by the leakage-currents of the transistors and as these are temperature dependent, the frequencywill drop very slightly with an increasein temperature. The upper frequency limit of the harmonics in the output will be determined by the rise time of the transistor used, that is, by the cut off frequency. Use of an R.F. transistorsuch as the OC45 or OCl69 will considerablyincrease this limit. 22 TRANSTsToR Crncutrs MalttJel No. 4

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ComponentsList Rl 1.8K Cl 0.005mf. R2 47 ohms CZ 0.005 mf. R3 47K C3 100pt R4 47K Trl OC70,OC71,OC45orOC169 R5 1.8K T12 OC70,OC7l,OC45orOCl69 R6 47 ohms Battery3 or 4.5V.

SENSITIVE SUBMII{IATURE RADIO USING A LOUDSPEAKER By using the OCl69 a receiverof small sizebut high sensitivity "un'U"-io"nrtructed without too many components. To obtain .um"l"nt R.F. gain a regenerativedetector is usedfeeding -a higl ;;i;- tw; transiitor A.F.-Amplifier. As a new lt" speakeris used ihe externaldimensions of the receivermay be 3" >" 2" x * inch or--The even less. speakeris the new TSL/Lorenz LP45F which is a moving coit tvp6 and has a depth of only |". The magnetis made from ierrit6'lnstead of the more usual alnico and this results in the i""i"OiUiv-is high field strengthof 9,500gauss. The voice coil im- o"Oun." i0 ohms and the output transformer should have a iri.ni iotio of 10 : I to match thii. This figure is noi, however, --itr"particularlY critical. iii"itit diagram of the receiveris shown in Fig. 9. The a-erial coil ihould be wound on ]" or $" ferriterod havinga lengthof I t" oi .oi.. Wind a layer of paper over the rod wide enough to hold Ll. Now rvind on Ll providing- alap at the tenth turn as ifio*" in tl.recircuit diagram. Use 26 gaugeendmel wire and wind itt. tu.nt side by side. The whole assemblyshould be wound sumcienttyfreely to enableit to be slid along th-erod. This makes it possibl-eto alter the inductanceof the coil so that the m'w' ir-uiA "u" be coveredaccurately' L2 should be wound with the iurn" cur,g" wire on a separatestrip of paper and should also be ablc-'-Th" td slidefreelY along the rod. trr.nt ratioof the interstagetransformer, T.1 may lie between 4.t: 1 and l0 : I the latter providing slightly more gain-than.th-e ioirn.i. the valueofthe eleclrolyticCapacitors is not at all critical, 8- or 10 mf. typesbeing perfectly suitable for C4 and C5' Wtt.o the-issembliof the receiveris completedit should be alienid as follorvs:-Set Cl and Rl roughly to their.mid positions ""&- rfiO. L2 with respectto Ll until the receiverjust oscillates' Iino-- oscillationsare obtained,reverse the connectionsto L2' if *iti now be possibleto bring the receiverin and out of or.iir"iiotrtv adjusiingRl. Cl is usedto tune in the station and Rl to adjusi ths amount of regeneration. It -ma.vbe-ne-cessary to -ouJ I- f" in order to cover the band properly in which caseLZ will alsohave to be n]oved' 24 r TRANSISTOR CNCUTIS MANU^L NO. 4

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ComponentsList Rl 50K volume control with srvitcirfor battery'-. Fortiphone iu"i VSZOavailable from TechnicalSuppiiers Limited' R2 i:bk ;trm iuu.i". C1 400pf'tuning cap' miniature iit izOk ottm submin. solid dielectrictype.or.post- ii4 jrc ot- submin. agestamptrimmerwithknob' nS 47K ohm submin. CZ 0'1 mf' ii6 if .tt- submin. C3 30 to 100 mf' 6 or more ni +.j rt or 10 : I interstage workingvolts' transformer. C4 6 ml'' T2 10 : I outPuttransformer C5 6 ml' iit oC169 Distributed bv Ll and 2 - Seetext' i;il;.ul SuppliersLtci. Loudspeaker' LP45F' Technical Tr2 oCti ;; ;q,ii'valent. Supplierl^Limited' i;; oclz "i equivalent. Price25iod' All productslisted as distributedby Technicalsuppliers I.imited .h;;ii;-;;;ir"ui"L.- vour local dealer but in caseof difficultv -"u t..6i"ined from TechnicalSuppliers Limited, HudsonHouse' 63,-GoldhawkRoad, London, W'12' '' TIIE " MIGHTY ATOM SINGLE TRANSISTOR RECEIVER This simplereceiver was designedby Weyrad for use with one "f ii,"i.-.ofit and is an interestingexamplc_ of. the excellentresults ottainaUtefrom a regenerativeclitector- which has been carefully desiened."'"fri"rV .i*ple transistorreceiver circuits are disappointingbecause to th;;;ili;;iy-rcceive the local station owing lt":l-:tllitllill; in ittit design,however, regeneration and a novel lorm ol aerlal i tivitv a-nd-selectivitv ;;t;11; ; ;;- "mplovea io i-mp rove bot h sens i"h[h ;d good^enough to permit..thereception of Continental the .i;ii"il. tt. t,igt pe'rformancewill also .proveattractive to *oi"^"ip"ii.nce.iconstructor who is looking for a simple_feede.r ;;ii1" G usedwith an existingamplifier or tape recorder' In such "ppfi*ti""t the overall sizemay be reducedby carefulre-arrange- ment"'ifre.iiiuit of the comPonentlayout' diigram of ihe receiveris shownin Fig' l0' and in Fi;.^il.;;;;hown"the modificationsrequiredfor long wave operalion' ;;?;;; tiJi'"g *"it the constructoris advisedto look carefullv at the diagramiso as to havea clearidea of thesequence of assembly. OperatingInstructions Although a six volt batterycan be usedthe setrvill rvork well on the"'pf 4.5 volt tYPe. "i iri in'Je.iat (a foot or two of wire shouldbe sufficientfor the and the bestpossible earth to the appropriatesockets. f..uiituiio"l preferably ffi;'hil;il;nes should be of the low resistancetype between40 and 100ohms. TnaNslsron Crncurrs Mam;ar, No. 4

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J 9 28 Tn.lNsrsroRCrRcurrs MaNuer No. 4 The receiver requires careful -swlt.h;;;a;i"Jirr"becauseit is ver.y and stations Juryng selective can easirvbe missed. - irii,ii control until the locai stationli tt.-J. tn'" plienuometer mav be used a,.sa volume control but for beit il;pii""'l;'rh.;ld''#";: vanceduntil oscillation starts_.-This is strow'n'uva howring noise. Reducethe control until .oscillati"".iirLii"irJ, ?s evidencedby the r..qption of the de.siredstation. rrris seiti-njli;; trometer:]31:I fit#: will needto be changedas the tuning-isui.ieo control ind ea.i, hasa sliehteflecr on thEother. n.ii i.irrt, *lllG;il";;.i bv reseiting :lightly- the tuning cip".rt.i""it.. ' the most sensiti'e position of the potintiomerernlu, tj..n iounJ.

1s-WATT PUBLIC ADDRESS AMPLIFIER The advantages of transistors.in public addresssystenls are, of .ogp,"_, weight, sizeand pori...orriurnp.,on. r nrs ledu,ggd amprrherwas designedby Mullard Limited and like to thank I woulrl them for theii permissioni;l;"il;. it in this manual. . The frequencyrespons.e, ;ensitivitt;nd- o"6ut power thansufficient are morc for the applicationior *fric[ ti!?mpfifier is intencled. being qi,i-te I:._'.::iliylty hieh enough t" ;;;bF; i;;;;;;ffi.; mrcrophoneto bc used. The Circuit The circuit diagram o^fthe unit is shownin Figs. 12.and 13. The outpur stageconsists of a matched_pair of oci6,sln;t;;;tricJ c.lassB push-puil. Despitethe ?c_tttrii uotniil-i.to., arecormected directlv to the nesativesid^e of the uiti.iv,Gi't.""iiii"^ as common .p"i"i! emitter amplifiersbecause ttid infut-fh"..u.o., is Uetweeri and emitterand Uir" not co,ilectorana e-itGi, for usinq thistype of circ-uitryisthat both i"tr*i"ii^.r. "iirr" an! ,"ir" i"tJliiiLi 4ay thereforebe connectedto u Co.n-onlleat sink. 0.5 ohm emitterresistors are-u,sed to p.*iAl-tt "in-,ai'rtaUitity"t high ambient temperatures.nVf S and RVZOproviOe bigs a forwartl to avoid crosioverdistortion ;"4 th"* ,h"i,ra rj"l"ol"io,iirri give 1^{juste{1o a quiescentcolrector aun;il;alo;A:il;ilt stage.. The- output transformershould be i" ifr. f"i_ o^f tappedchoke ;;;; having a total d.c. resistanc"-ir,"i,oi l.r, than 0.2 ohms and an inductanceoi more ttran iob mii. component home made. may be The driver stage usesan oC26 as a classA amplifierdissipatine a total of about t.J watts. The co'ector iuireil;i;;td to the #;;iilA; correct level, l25mA., Uy mians-oi-ilnfi- Th;;ffi;; I \ TR.q.NsrsronCrRculrs MlNuar- No. 4 29

should be mounted rvith a mica washerbetween it and the chassis. The specifications for the driver transformerare as follows:- Turns ratio 2.5 : | * 1 (bifilar secondary) Primary Inductance )500 mH at 120mAd.c. Primarv d.c. resistance (6 ohms Sccondaryd.c. rcsistancc 5ohms*5ohms lf the rcsistanceof cach of the secondary w'indings is less than l 5 ohms t 10i/. they should be brought up to this value by the ,) lddition of a seriesresistor as shorvnin Fig. 13. The thrc-e preamplifier stages are fairly conventional, the most '.-rnusualpart of the circuit being the use of direct coupling between tire second and third transistors. The high frequency response is limited to 7 Kcls by including C6 in thc feedback network. There is no point in amplifl,ing frequenciesof more than 7 Kc/s particularly u,hen to do so results in an increase ia crcss over distortion in the ()utput stage. As reproduction belorv 150 cis is not desirable in a public address arnplificr, the lorv frequency response is limited by rnaking Cl0 4 nru.f. instead of 10 mu.f. Thc supply voltage of 14V \\'as chosen becausethis is the typical ralue lor a fully chargcd 12v. accumulator as used in cars, The rinrplilicr rvill, of course, still operate properly when the supply loltage drops below this value. The performance figures supplied by MLrllards for this ampiifier arc as follon's:-- C'urrentconsurnption-no signal 220mA. specch& nrusic S00mA. approx. Scnsitivitl (lor full output) 0.2uA. 0.2 mV. l '."',t i,'.na,-I.^^^ r "Pqr l,,y!ucrrr!v 1K ohm l)istortionat full outnut lessthan 4f lrreqrrcncyresponse 150to 7,000c/s * 3dB.

TR,INSISTOR YOLTN{ETER \!hcn mcasuremeutsof voltages are made in high resistance circuits care nrust alual's be taken to ensure that the resistanceof the meter used is greater ti-ran that of tl'ie circuit being me;tsured. preferably by a factor of ten. The conventional moving coil or rloving iron meter rarely has a sufficiently high resistanceand elccironic and service engineers almost invariably use a valve loltnrcter in place of this. Valve voitmeters are rather expensive pieces of equipn.rent and arc usually priced be1'ond the range of the a-veragehome con- stnlctor. Ilowever, a transistor voltmeter, such as this one, may have an equally high input resistance and be, in every way, com- parable rvith its valve counterpart. In addition, it has several advantages being far smaller, lighter and, above all, independent erf c.rtcrnal porvcr srrpplics, Tnrr"srsron CrRcurTs MeNu. r, No. 4 i" I

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|l', TnaNssroR Crncurrs N{aNu,q,rNo. 4 33 The circuit diagramof the unit is shown in Fig. 14. The input resistanceon-the highcst range is 15 M ohms ai.rdis generallyl5bK ohrns per volt. The-nrodqof operation is simply cxplained;rvhen a voltage is applicdto thc input it will causea smallcurrent to flow througfrthe input rcsistorand the basc-enrittercircuit. A considcrabtyamftineO version of this current rvill ,flow through the collecior-einitter circuit and rvill defiectthe needleof the micro-autmeter. Taking a typical cxample let us assumethat the input voltage is 1 vol-t arrdthat the su'itchis in the positionshorvn in the dia-gram.The base-cnrittcrresistance is lorv enoughto be ignoredso ihe current this genclateswill be, by ohm's larv, 6.7 nticroanrlts. Assuming a cu_rrentgain of 40 timcs, rvhichis typical for an OC7l, this wilt resultin a collectorcurre nt of 268 microamps. This rvill be shared betweentirc meterand thc sensitivitycontrol-so that only 100micro- . amps actually flows through the meter to r;roduce full scale deflcction. In thc absenceof an input voltagethe transistorrvill still havea collectorcurrcnt rvhichrvould tend to cleflectthe meter and nrake accuratercadiugs impossible, so a caircelling- current in.the oppositedirection is providedby R5, R6 and B2. -I]9fqreusing the meter,short circuit the input and adjustR6 until thc lletcr rcadszero. If zero balancccarinot be obtainedin thc cool positionof S2, closethis srvitchto thc lvarm position, but rnakcsure that R6 is not turnedto too low a valueor themetei uill-bc damagccl. Now connecta kno*'n voltageto the input (such.asa lr4allor-vnrercury cell uhich is 1.34\')aid adjustj{4so thatthc dial indicatcs this value. 'a If you alrcady possessa multimeter, rvith 100 uricroanrp rangc.thismay be uscdand the rcst of the componentsrtray eithir be built into thc cascor incorporatcdas an add on unit. ComponentsList RI 15NI ohm Il2 1.5l\{ ohnr R3 150Kohm R4 10K ohnrpotcntiometer R5 47K ohm 20i.j R6 50K ohrnpotcntiometer S1 Singlepolc, threeway srvitch S2 Singlcpole, on/off switch Bl & Bl Singlepenlight or slim penlightcells Tlansistor OCTl or equivalent M 100microamps F.S.D. .The two batteriesmay be.solderedinto the bircuit and will'last as long as their normal shelflife becauseof the tiny currint drain of the unit.

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SItrIPLE EARPIECE REFLEX RECEI\/ER Tlrc lcgcncrative,'reflextlpe of receiver has norv become quite commonplacc and, becauseol the small number of components required for a good level ol perfornrance,is almost invariably uscd in the cheapcr t),pc of kit. The principle of the circuit is sinrply that the first tlansistor, bcside-samplifying at R.F. is reflexed to amplify. at A.F. and act as the dri!'er for the output stage. In addition to this, regeneration is olten employed to incrcase the R.F. gain and sensitivityas in the receiverdcscribcd herc. Many ol the designs llrat iravc been produced ancl described in books and jor.rrnals gii'e excellent pcrformance but lhey rarel;- lend then-rsclvcsto nriniaturisation becausctircy use Il.F. chokes *'hich arc cnly available in rathcr large sizcs. This sct, horvever, has bcen dcsigncdspecifically to ar,oid thc usc of any translormcrs or chokes and nray, therefore,be built vcry contpactl)/. The tur.rcclcircuit consists of a smail fcrritc rod aelial. L. ar:d a postagcstamp trimnter u'itl.ra knob littc.rlto it's 68A scrcu',Cl. Thc aerial coil is tapped to match the ilrpLrt intpcdance of Trl, an OC44. Thc signal is fcd to the base Ironr tlic end of tlie coil rather than fron-r the tap so that feedback fron.r thc collector',rvhich is 180" out of phase u'ith the basc, may bc applied to the other end. The phasechange resulting fronr the finite transit tinte in the OC44 is small enough to be ignored at mcdiunl \\'avebandfi'cqucncies so this arrangemcntrcsults in positive fecdback. The R.F. output from Trl is ntainly fed to the t*o diodes via C4. A srnall proportion, however, is fed back to the tuned circuit via Rl and C2 to provide regeneration, The collector load for Tr1 is resistiveand has a total value of 10 K ohnts, split into two 5 K ohm resistors to separate the R.F. and A.F. outDuts from the transistor. The R.F. ourput is dcmodulatcdby Dl anOOZ and the resultant A.F. signal applied to the base of the transistor. The output from Dl also contains a D.C. component which is pro- portional to the signa-land tends to reduce thc base bias on Trl thereby reducing the collector current, since the gain is very dependent upon operating current in this type of circuit this system provides a high degree of A.G.C. and also prevents oscillation at high signal levels. The ,.r.F. output from Trl is R.C. coupled t'o the output stage. This stage drives a hearing aid type earpiece or a pair of high impedance headphones. The impedance is not very critical and reasonable results will be obtained even with low impedance units but high impedance types certainly provide more volume. The total current drawn from the battery with this set is only about * mA so the type of battery you need will depend upon the case size. For very small receivers the Ever Ready D22 is ideal as it is only 1t" long x {-" diameter. =

TuNstsron Ctncutrs N{arunl No. 4 35

ConstructionalDetails The only componentthat hasto be home madeis the ferrite rod aerial. T[is consistsof a total of 55 turns of 34 gaugeenamelled wirervound on a ?I" lengthof ferriterod with a tap ar-the I Othturn. A singlelaycr o[ paper should be rvoundbetlveen the rod and the wire. The layoutis not criticaland ma1'bc arrangeCto suit the ccn- structor. An ideaof how snrallthe setn13y be madeis givenb-v thc diagramin Fig. 16. This diagran.rjust shori'sthe positioningof the main componerttar.rC may be uscd as a guide by-the constru-ctor. Varying'thcvalue of R2 may improvethe performance.With sonretransistcrs 800 K or 500K may give betterresults. In operationR1 is usc'lto controithe regeneration and hence the volume. Beforctuning irr a stationit shouldbe adjustedjust short of the point of oscillationand then readjustedfor rraximum performance- when the rcquircd staticn l.rasbeen selcctedby Cl, Like all rcceiversusing ferrite rod aerialsthis set is directional and s,ill receivesignals best when turrred at right anglesto the directionof the transmitter. If the sizeof the recciverdoes not ll'latter,performance being a major consideration,R4 may be replacedby an R.F. choke oi I to 5 mH. inductanceand R5 by an A.F. chokethe value of rvhicl-r is not critical. If thcseadditions are made,care nlust bc takcnto ensurcthat no inductivecoupling occurs between tire R.F.C. and L. For allrcasonable signal strcngth areas, however, these addititlns are unnecessar]'. ConrponentsList Rl & S 50 K ohr-nvoiume control rvith srvitch (Fortiphone type VS26is suitable) R2 1 N{ ohm or less(see text) R3&R4 5Kohm207( R5 120K ohm201i Cl 250pf. postagestamp trimrrer CZ 5 pf. C3 0.001mu.f. C4 100pf. C5 1 mu.f. 3 volts working or more. Any highervalue of capacitorwill be satisfactorY. L 55 turr.rs. 34 gaugewire on 1" ferrite rod (seetext) E Hearingaid type earpiece. 1 to 8 K ohm impedance B 3 volt battery Dl & D2 Mullard OA70 Tr1 Mullard OC44 TrZ Mullard OCTI -

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! TnlNsrsroR Crncurrs Mltr.r.ler, No, 4 39 STMPLE TRANSN{ITTER In Transistor Circuits \{anual No. 2 details and the circuit diagramfoi i simple3 transistortransmitter are given' That.unit il.4 ; u".l"Uf" fiequency oscillator and-a moduiator arnplifier' A.r .u.n simpler transmitier can be built for use with a morse key and-' with a ciystal controlledoscillator. 'It ihe circuit diagru^ of sucha unit is shownin Fig'. U' is not oniv iirnpt" to b'uild but sin.rpleto operate as well becausethe iiuitul .ti*r.s ciiittation at the correcl frequency. The circuit is a variationof the Colpittstype of oscillator,withthe crystaland bi'6fii"; i capacitaiivetip acrossthe collector load which is i I .s oi Z.i n illi.'Hcnry R.F. ihoke. This systenrprovides positive feedbackfrom collector to base and sustainsosctllatlon ln tne ;;)"t"t:- Cl- iontrols the degreeof oscillationand doesnot alter the- -tir" frequency of oPeration. iiuntritittir may be operatcdby a nor.maltransmitter key or, if a'ieaffv smiii-""ii is required, by-a microswitch. The aerial ;t b"; roa type having a length of betweenI and 2 feet' The ".Vitul nur, of course, to-be cho-sento suit the lrequ.elgyrequired which should bc somewherein the top amateur bancl'that ls Irom 1.715"fft" - 2mcls. tung"'obtainabledepen

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40 Inrlslsrori Ctnturts }lrll'rt No. 4

N,{IIES .\\-D ADDRESSI,S OI ITANUI,.ACTURERS

.Ardcnlc Acoustic Laboratolics. Lintitcd, 8il:, \lincrva Road, l-ondon, N.W.l0.

llrrrsh (irystal Co.. l.inritctl, Shtrrc Rrrad. H11hc. Southampton.

Ct,lne t:lectric, l-inritecl,[]urr' [..anc,Ricknransworth. [-lerts.

Ldrsuan, Limitcd, 15.5.Charing Cross Rt,ad. London, W.C'.1.

ljort.iphone,Limitcd, 91, \.liddlcscx Strect, London, E.l.

G.E.C. Limrted, Nlagnet Flousc, Kingswal', London. W.C.2.

I'lallori' Batterics. l-inllcd, Ral'nhant Works, Rainhanr Road S,'uth, Dagcnharn. Ilrscx.

i\lullard. l.imited, ivlullarrJ II,,usc. forringlon I,laec, I_ondon, w.c.t.

Newnrarkct Transistors. I_inrited, t:xning Road, Ncwrnarket, SufIolk.

Parrrcko.Limited, Percl Road. A-vlestonePark, Leicestcr.

Semiconductors,Limitcd. Cheney'I\.{anor, Swindon. Wilts.

TcchnicalSuppliers, Linrjtcti. Hudson Flouse,63, Goldhawk Road, London.W.12.

Wrngrore and Rogcr:. l_irnitcd. Dornville Road. l\lill Lane, l-ivcrpool,1.3.

I he OC169 transistor and tire [,P4-i L.oudspeakerare distributed throughout Gt. Britain and thc British Commonwealth bv TectrnricalSuppliers [-td. and ntay be obtained from your local .lealer.

r.' I' i SERNARDSTUDIO BOOKS No. 56. Radio Asrial Handbook 57. Ultm-ShortwaYc.llmdhbok 5E. Radio llintr Mmual 64. Sound Equipmcnt Manuel 6E. Frequency Modllation Receivers' Manual 83. Radio ltrstrumeDts and thcir Con3arocaiot ... 96. Crystal Set Constrrction 99. One ValYe Reccivers 100. A Comprehensive Radio Valve Guide, Boot I "Radiofolder" ... 103. A. The Master Colour Code Ind€x lor Rrdio snd. T.V. 104. Three Valve Reccivers . l2l, A Comprehensive Radio Valvc Guide, Book 2 "Radiofolder" ... 123. F. .The Beginners' Push-Ptll Amplifier ... 126. Boyc' Book of Crystal Sets and Simple Circuits ... 129. Universal Gmm Motor Speed Indicutor ... ; ... 135. All Dry Baatery Portrble Comtructiol l3E. How lo Makc F.M. and T.V. Aerialo, Bandr 1, 2 rnd 3 t4t. Radio Senicing for Amatern i ... 143. A Comprehcncive Rsdio Valve Guide, Book 3 .,, 145. Handbook of AM/FM Circuiti aDd Compon€ntt 146. High Fidelity Lou.Ispeaker EDclosur$ l4?. Practical Tspe Rccorditrg'Ilandbook l4t. Praclical Tmmistor Rcceiveis. Book 1 -{ l\

l7l. Super Sensitivc Ttansirtorised Pocket Set Conslructlor 172. Intenatiotral Radio Statiom List ... 173, Practical l?aDsislor Audio Amplifierr ... 174. Transistfi-Subminiature ReceivcE llandbook 175. Trmsictorised Tst Equlpmetrt and S€ricirg Manusl ,., .,. ' 176. Transistor Ardio Amplifiem Manual t77. Modern Tmnsistor Circuits for Beginnere , l7E. Comprchensivc Radio Yalve Guidc Book 5 179, Transistor Circqitr Maaud No. 5 ... + 1E0.. British Scmisrductor Suncy ,l\ lEl. 22 Test€d Circuitc Using Micro Alloy Tnnsirtorr q lE2. "At A Glaoce" Radio Yalvc & T.Y. Iubc Eqliyslents lE3. How to Receive Foreign T.Y. ProgHnmes on lrour Telerilion Sea by 1. simple Modificationr b It4. Tesied Transistor Circnits llandbook lEs. Tested Short-Wayc Receiver Circuitt using Mico Alloy Trsn3fulon (MAT's) lE6. Tested Superhet Circuits for Short-Way3 and Commtnicalion Reccivorr using Micro Alloy Tmnsistors (MAT's) "4" lE?. Thd TSL Mark Valred F.M. Trncr and its Constnctlon ... i 188. Construction of thc B.H. lligh Fidelity ..14" watt Audio Ampllffer ... lE9. How to build the world's smallest transislor ndio. ThG Sinclair Micro 6 190, How to build the world's mallcsl lligh Fidclig Ampliflcr .., l9l. Praclical Car Radio Hanalbook 501. ABC'! ol Magnetism 502. ABC'8 of Misrilc Guidance ... 503. ABC's ot LrltBonica 504. ABC'g of Transirtor.' Resistor Colour Codc Disc Calcolator Engiirecrc' Refcrcnce Tabler Itrleilational Radio Tubc Encyclopaedia-3rd Ediiior ...