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'  J GENR  AL R  ADIO EXPR  IM  NT

I N 1 JUE

Announcing a

New General Rado Srvcefor Experimenters

There are ma phases of radopartculary concerg he deveopmen o apparaus and is appcaion oher ha s more commouses n broadcas recepon-inwhch here is cosiderabe neres.

o suppeme he echnca formaon aread conained heeadg rado magazines, he Ge

era ado "Expermeer wi bessued eve moh o provde heeperimeer wh reabe daa andhepfu sggesos which ma bep o good use n he home aboraor I w aso revea some of heneresg nformaon whch exesve research n he GeneraRado araoy as eded.

he opc chosen for dscusso hs ssue reas po a subjec iwhch here s a wde neres, namey-b qi re

he mproveme n qua has

come about prncpa hru he desig o eer ubes, audo amping rasformers and odspeakers;he probem of paricar eres ohe eera ado Compa bengha o ransformer desgn.

I wi be remembered ha 19 I he s audio ampifg

ransformer havng a cosed corewas roduced b he enera aio ompany A a me cosed core was ooked upon as aradca deparre from he opecore pe which had bee he standard pracce. I was o og however before hs tpe of ransformer

was adoped b pracca a radomauacurers

Sur T Rur

End Pard

"Tl1e Exprimn' i l be pu·s th ro

of suppyg uba nnp d ap •ign

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c L r n Lhorou hly

j r hrh -pn n-i hl cn nreqe o OUwi yz c w copihor im.

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Improved uai o broadcasg,reproducn insrmes, ad beerubes mae t ue desrabe o mprove rasformer desg si frher ad o ee ew codos heenera ado Tpe 28 rasformers were deveoped

he ace o asformer desig coained n his ssue C .Brke of he Egeerg Deparme gves some ver teresngad srcve daa based onmeos aboraoy experimets

ampcaon ad measremes ofvarous pes of ransormers.

July Issue of "The Experimenter o Cn-an Trae n "B Enao

Whe compee bate emnao has o e reached a sagewhee is geera sasfacoy orrecevers empoig varous becombiaos, grea srdes are beg made ha dreco ad oday he "B emiaor, because of

is unfang pae voage and reefrom he bother o cona baerepacemens bds we o ecpe oa arge ee he se of B' baeres.

Ahough he succesu operaoof a baer emnaor dependsudameta pon he recidevc, he use of we desgnedrecier ransorme and erchokes s mperaive

Cosderabe research as beencoducted n  the  General Radio 

aoraor upo s subjec whchhas ieded a so1e o eresig nformatin  which H. W. Lamson,

of he  Engieering  Departmen wildscss hs arce o B baeremiao he J sse.

Fure ssues of he permener' w conai arces o popuarengneerng subjecs and fomao cocerg he deveopmeand processes of maufacure ofvarous srumes.

I s hoped ha hr hs medmhe eperimeer ma become morefamiar wih he nderg prncpes of apparaus desgn ad appcaon so Lha he a have a morecompee ad accurae knowedge o

rado upo whch o base hs expermena acves.

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X P ER I J   NT    

sstance of the curves of Figs. 2and 3

In he audio amplier the trans-former prmay is connected in seres wth the pate impedance of thetube, which is about 15000 ohmsfor the common type of receivingtubes A considerable portion ofthe voltage suppled by the sgnalis used up in ths impedance. Theportion of the voltage left across thtransformer pimary depends uponthe relaton of transformer impedance to the total mpedance oftransormer and tube Thus if thtube impedance s 15000 ohms andthe tran former mpedance 30 000tothirds of the voltage wil be pressed across the transformer prmary. t wil ow be se n why a highratio transformer sometmes givesess amplication than one of loratio. Suppose a 5 : I transformerhad 150,000 ohms mpedance at acertain frequency Another transformer with an 8 1 rato has but 15-000 ohms imedance n the prmary Both are used wth a 15000

Fig 3 The L 1 lLc imp <n o

f a ausfrmr high prir dn he nd hw imp r mki mrt w r bi·auc i �ri "it h Lmrrimary thri n tr l f. m-

r m «O <

ohm tube, wth 10 volts avalabe.The 5: 1 transformer wll have 50QO 1�.oc cf vols o 93volts across the prmary Assumngno losses the secondary voltagewould be 47 volts Only 15000/30000 or 5 volts ll be impressedacross the primary of the 8 I transformer with a secondary voltage of

40As the transformer impedancvares with frequency while the tubeimpedance remans constant the input to the transformer vares overthe frequency range Ths of courseresults in distorton (unequal outputof derent frequences). D tortondue to this cause can be reduced bymeans of a hgh primay impedanceTe input to the transformer cannotbe greater at any frequency than thetube voltage. f at the owest frequency t s intended to ampify, thetransformer mpedance is three

times the tube impedance the input will not be le s at any frequency

than 75 per cent the tube voltagethat  s, not more  than  25  per centderence n amplcaton of dierent frequencies can occur. On thother hand,  if  the transformer hasbut half the tube impedance at thfrequency the dierence ll be 6per cent.

The curves of gure 2 were taken

on transformer o 1 using dierent values of plate res tance fthe plate resistance could be reduced to zero even ths transformer would gve ltte dstorton Thecurve becomes more and morepeaked as the value of Rp is ncreased, and the ampcation perstage is greaty es ened In gure3 is shown a simlar group of curvesfo transformer o. 4 This i

transformer of hgh primary mpe-dance I 5 5 000 ohms at 1000 cyclesas compaed to 15000 for o I twill be seen that while the curve is

b tter for the ower plate resi tancesthe derence is much ess markedthan in the case of o. I The advantage of a tube of low plate mpedance s obvious That is one ofthe advantages of the new C. Atubes.

We have shown the essental requrement of equal amplcation ofall frequencies to be a high andneary equa impedance at all frequences Ths is accompli hed bythe use of many turns of wre, wtha large core of hgh permeabtsteel and by proper coi design

avoiding capacty that acts as a bypa s for hgh frequency Ths requrement may be met in a trans-former of hgh ratio as wel as neof low.

o far we have been dealing wththe probem of the manufacturersThey have met t with surprsingsuccess a veral of th new transformers show t s up to the builder to make the best u e of the manufacturers' eorts and not spol theresult by touches of hs own

Many rado bulders think it anadvantage to shunt ther transform

ers wth condensers or grd eaksWhile this practice oetmes helpedto improve qualty wth the old typetransformers with a transformer ofgood design it generally ruins quaty

A condenser across the primaryof the rst audo transformer is usually advisable and may be as argeas 0005 microfarads without a ectng the fathfuness of reproductionDevices cross the secondary arepartcularly harmful ig. 4 shosthe eect of several szes of con-densers and grd leaks across the

secondar The eect of the condensers on transformer o 1 shown

Fig . 4. goup f  UT\ e  b wing  L  e ctof huig   varu d,ice  rs h  trn - rmr nr h p r r wrn wih r tr nf rm r, lwr

th nw'r

·n  the  upper hlf of  the gure tomake  stll more marked  the peakn the central portion of the curve.The  hgh  frequences  are cut o  withncreasng  efectiveness  as  the  size

of the condensers  is ncreased. It   nterestng  to note  that  at some frequencies resonance  eects  carrythe  curves  with  shunting  condensersabove  the normal curve.  The useof grd leaks mproves  the  qualitywith this poor transformer With aleak  of 1.5  megohms, a  curve sim-ar to o. 2  of gure I obtaedThis curve is poor but somewhatbetter than the normal one. Whenthe shunting resstance is reducedto  200,000  ohms a very  at  curve is obtaned, but the 8 transformergives  ess  ampicatio  than   2 : 1. 

The eect of shunting condensersacross the secondary of transformer

o. 4 is similar to that observed inNo The ampcaton of highfrequencies s greatly reduced withthe point at which the curve fallscomng farther toward the low frequencies as the condenser sze is increas d improv ment in quality ganed by shunting the secondarywth a resstance is not so markeas with the badly peaked ransformer. A great los o volume iscaused by this practce With the2000 ohm ressance across the

secondary the amplication is cutapproximatey in half with no greatmprovemnt in quality

The rao set can be made to reproduce music as fathfuly as theaverage phonograph, or even moreso. f this is to be accomplshedthe whole amplfyng and reproduc-ng system must e lad out iththis purpose in vew Good transformers must be used in the aythe manufacturers intended them tobe used. Tubes must be properlybiased and not overloaded andnally, all other precautions are in

vain unless a good reproducer isuse

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"By ye deed hall e be known, aold yet sgnant poverb hat applie todu a well a to the ndvdu It b aal hat poee onzaohch s pu ued a seada t poly ofey hould be he pe en da leaden t pariula eld o endeavo

The Geneal Rado Compay has a·

ned t po o as he ou tandn! mauatue o ado pa ad laboraon ume houh e eognzed mertso s podu .

Sne he ealy d o do amaeuoperato and et-bulder have lookedupon e Genea Rdo ompay a ameed podue o depedale appatu

e aeul and o evave byer oro p loo s to the epuaton othe anue He nos o s owe ·perience and ho e o oher whehe

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h epuato arant s odee hs elf ame odne upon hhhe popula preeree o eneal aoat s ba ed

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A cq h Gel ad Cpanyh gnd h sm and ondnce of mu x- ha gpwho e thughy falr ih  the thnq ofd d  d h h c d uh f t apd d,

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