LABORATORY. ELECTRONIC ENGINEERING · 2020. 11. 1. · John Ambrose Fleming was born on 29...

COMMUNICATIONS DEVELOPMENT LABORATORY.

REDIFON LIMITED, WANDSWORTH.

ELECTRONIC ENGINEERINGVOL. XXVI

NOVEMBER 1954

CommentaryAMONG the principal celebrations to mark the Jubilee of the

thermionic valve which occurs on the 16th of this month is thatorganized by the Institution of Electrical Engineers. On thisoccasion the proceedings will be opened by the Lord Presidentof the Council, the Marquess of Salisbury, and there will followpapers by Sir Edward Appleton, Professor G. W. 0. Howe andDr. J. Thomson, which together will trace the history and develop-ment of the thermionic valve since its inception fifty years ago.

The celebrations commemorate the application on 16 November,1904, by Sir Ambrose Fleming for his British patent to cover therectifying properties of a device which both he and Edison had, infact, independently discovered some years previously in connexionwith their investigations of the carbon filament lamp. At the timeAmbrose Fleming was Professor of Electrical Engineering atUniversity College, London, and it is therefore appropriate that theJubilee celebrations should include a conversazione at the Collegewhere so much of his work was done.

An appreciation of the work of Ambrose Fleming is to be foundelsewhere in this issue and a fuller account of his activities waspublished in 1949 on the occasion of the centenary of his birth*,so that to deal in these columns with the events as they occurredat the time would be merely repetitive.

The growth of electronics has, of course, been phenomenal,particularly in the post-war years and so rapidly does the progresscontinue that any forecast or prophecy of the state of developmentwhen the centenary of the valve is celebrated would be very wideof the mark. To attempt to look ahead fifty years we have onlyto turn back by the same time interval to realize how far we havecome. Certainly, fifty years ago Ambrose Fleming could not haveforeseen the enormous revolution the valve was to bring about.Both he and Edison had already observed the unidirectional flow ofcurrent across the space between the filament and the " plate "of the early carbon lamp and what we are, in fact, commemoratingthis month is no more than an inspiration on Fleming's part whenhe applied this simple rectifying device to a wireless receiver whileacting as a consultant for the newly -formed Marconi Company.He could not have realized that that simple experiment, taking nolonger than an afternoon to carry out, had ushered in the electronicage that was destined to speed up enormously the tempo of ourlives and to contribute inestimably to our well-being. To many ofus fifty years ago is not a fading memory but a matter of historyand we can have no intimate knowledge of those spacious leisurelydays of 1904.

We are accustomed as from birth to these modern miracles thatwere absent then, and we take for granted the fact that from thetelephone at our side we can speak to the ends of the earth and thata mere turn of a knob on a radio set carries us from continent tocontinent. It is no longer a wonder to us that from the comfort ofour homes we can see events as they occur hundreds of miles awayand that daily our range of vision is increasing. These are now the

MACGREGOR-MORRIS, J. T. Birth Centenary of Sir Ambrose Fleming.Electronic Engng. 21, 442 (1949).

No. 3 2 1

everyday occurrences that are part and parcel of what we call ourimproved standard of living.

Yet it is perhaps in the scientific world that the thermionic valveis making its greatest impact for, by its aid, many of nature'smysteries which hitherto had baffled us, have now been forced toyield their secrets. It is true to say that there are few physicalphenoniena which cannot be measured and displayed by electronicmethods and that, as a result, our knowledge has increased enor-mously. In no period of our history has scientific progressproceeded at such a pace as during the last fifty years, and it isdue very largely to the thermionic valve.

An event of considerable importance to the economic well-beingof Scotland took place last month when His Royal Highness theDuke of Edinburgh opened the new electronic research laboratoriesof Ferranti Ltd., at Edinburgh.

For some years concern has been felt at the continued drift ofindustry to the south, and the Scottish Council (Developmentand Industry) has been much occupied in arresting this trend anddevising ways and means of producing a more balanced industrialeconomy for Scotland.

The manufacture of many new light engineering products suchas aero engines, office machinery, clocks and watches has beenadded to the range of Scottish production, but several of thenewer and more important branches of engineering industry havenot developed to any great extent and electronic engineering isthe most prominent example.

The inadequate growth of this industry in Scotland-country ofworld renowned engineering tradition-has meant that not onlyhas it not shared fully in a major and growing source of employment,but that the basis from which will come the more important pro-ducts of the future has not been established there.

Some five years ago, therefore, the Scottish Council set out tointroduce electronic engineering into Scotland on a wide front andinstituted discussions with the Ministry of Supply, the Admiraltyand several Scottish firms. At that time, Ferranti Ltd., were theonly firm in Scotland with research laboratories of worthwhile sizeand they agreed to act as a channel through which some Govern-ment electronic contracts might flow.

They also undertook to train engineers from Scottish firms intheir laboratories to acquire the new techniques and to act as aseedbed from which young electronic teams could be transplantedin due course to other firms.

This scheme has been operating for some time past, although on arestricted scale due to space limitations, but now the Ministry ofSupply has provided a new laboratory to accommodate not onlyFerranti's own research staff, but a nucleus of 40 engineers fromother firms. The opening of these new laboratories is an excellentexample of co-operation between Government Departments, theScottish Universities, Technical Colleges and industry, and itwill prepare the way for the development in Scotland of a newmajor industry.

NOVEMBER 1954 465 ELECTRONIC ENGINEERING

7' 44-44

it.4.¢77t

Facsimile of part of a letter written by Flemingto Marconi (circa 1904), announcing his discovery

of the "Oscillation Valve."

y e

41zieve.0

FIFTIETHANNIVERSARY

OF THE

VALVE

An appreciation of the work ofSir John Ambrose Fleming,

M.A., D.Sc., F.R.S.By W. J. Baker*

IFTY years ago, on 16 November, 1904, an insignificant-': looking sheaf of papers was handed in at the PatentsOffice in London, to be filed, in due course, with thethousands of its predecessors. There is not the slightestsuggestion that those documents caused even the lift of aneyebrow in that temple of inventive aspirations; yet, hadthey but known it, the clerks were holding in their hands aconception that was destined to affect, to a profounddegree, the future of the entire human race.

The papers described an apparatus termed by itsinventor an " Oscillation Valve ". The applicant for apatent was John Ambrose (later, Sir Ambrose) Fleming.

But even the most imaginative official in the PatentsOffice might well be forgiven for failing to appreciate thepossibilities of Fleming's idea. Indeed, in that heyday ofthe Machine Age the apparatus must have presented awoefully improbable appearance to the lay eye; for herewas no intricate piece of machinery to quicken the brainand promote visions of power. The entire equipment, itseemed, consisted merely of an Edison, or Swan, type ofelectric lamp to which had been added, inside the glassbulb, a few square centimetres of metal plate.

Even Fleming himself could have had no idea, at thetime, of the far-reaching consequences of his patent. Thathe had solved the problem of providing a sensitive andreliable rectifier for the high -frequency currents of wire-less telegraphy he well knew; but that he was, at thesame time, witnessing the birth of the electronics industryhe could have had no inkling. This is evident when, in hiscapacity as consultant to Marconi's Wireless TelegraphyCompany he writes a personal account of his experimentsto Marconi, and concludes by saying: " I have not men-tioned this (oscillation valve) to anyone yet, as it maybecome very useful."

Fleming lived to see his words become a classic of

* Marconi's Wireless Telegraph Co., Ltd.

ELECTRONIC ENGINEERING 466 NOVEMBER 1954

conservative understatement. Less than fifteen years later,R. D. Bangay, in his text book " The Oscillation Valve "could say, in preface: " The invention and improvementof the Oscillation Valve has led to important and far-reaching developments in the art of Wireless Telegraphy.The new fields of possibility opened by the invention haveas yet been only partially explored, but already the per-fection of the wireless telephone and of the wirelesscompass are directly due to its agency."

Today, with a fifty-year span to review, those remarksare as apposite as when they were written in 1919. Theintervening years have undoubtedly unfolded a multiplicityof applications for the thermionic valve. To the " wirelesstelephone " and " wireless compass " one could add adetailed list to stretch far beyond the bounds of thisarticle. Broadcasting, television, radio communication,radar, diathermy, ultrasonics, guided missiles, airborne andground navigational equipment, radio facsimile, radio-thermics, sound amplification (from public address systemsto deaf-aids)-all these, and more, can be added to thequota. And all of them stemming directly from Fleming'sapparatus.

Almost daily, fresh applications confront us. The broadclassifications given above are splitting, amoeba -like, intosub -divisions, each tending to become a specialist indus-try in its own right. Radar, for instance, which beganexistence as a desperate expedient for giving advancewarning of the approach of hostile aircraft, has developedin innumerable directions, and today only the most basicof first principles can give a common denominator betweena c.x. radar station and, say, the proximity fuse.

To quote only one more example-television, whichbegan solely as a means of entertainment, has morerecently expanded its aims to include applications inindustry. Prophecies are always dangerous, but it seemsnot unreasonable to suppose that in the course of timethe manufacture of industrial television equipment maybecome the senior partner of the two.

All of which is a far cry from 1904, but it is beyonddispute that the valves of the mighty transmitters of todayare in direct line of descent from that first thermionicvalve patented by Fleming. But although it is this particu-lar anniversary we are commemorating now, it would begrossly unfair to forget that, had Fleming never inventedhis " Oscillation Valve ", his many other achievements inthe field would still have rendered his place secure in theHall of Radio Pioneers.

John Ambrose Fleming was born on 29 November,1849, near Lancaster. Five years later his parents movedto the London area, where young Fleming was to spendmany years. It would seem that from his earliest days he

Sir Ambrose Fleming's original experimental thermionic valves,the forerunners of all modern wireless valves (1904).

NOVEMBER 1954

Early Marconi production models of the Fleming diode,forerunner of all thermionic valves.

was possessed of that blend of patience coupled with aninability to take things for granted, which is one of thehall -marks of the inventor.

At the age of fourteen he was sent to University CollegeSchool, where his bent for engineering became even moreapparent. Three years later, his parents being unable toafford the expense of an engineering apprenticeship-thepremium demanded in those days was quite considerable-young Fleming got a situation on the clerical staff of theStock Exchange, and continued his studies at home, underthe University of London External Scheme. Beforehe was twenty-one he had taken his B.Sc. degree, FirstClass, there being but one other to do so in that year.

Fleming's restless, inquiring nature seems to have madehim somewhat of a rolling -stone for some time. Heobtained a post as Science Master at Rossall College, butremained there for only eighteen months. There followeda lengthier spell at the Science Schools, South Kensington,where he studied under Dr. Frankland. His most notableactivity here was the part he played in the founding ofthe Physical Society; the first paper ever read to thatbody was, in fact, Fleming's.

Soon, however, he was on the move again, for a briefsojourn as a science master at Cheltenham College, butin 1877 he resigned the post, having won himself aScholarship to St. John's College, Cambridge. This wasindeed a great day for Fleming, for it meant the fulfil-ment of a cherished ambition-the opportunity to studyunder the great Clerk Maxwell.

Maxwell's death in November, 1879, filled Fleming witha deep sense of personal loss. Shortly afterwards he leftCambridge to take the post of Professor of Physics andMathematics at Nottingham's University College. But,hardly had he unpacked his belongings there, when anoffer arrived which called upon him to make what trans-pired to be one of the most momentous decisions of hiscareer.

The proposition emanated from the Edison ElectricLight Company of London. Fleming became electricaladviser to that company and so began research work onbehalf of the Wizard of Menlo Park. It was during thecourse of this that he made his first acquaintance with thephenomenon known as the Edison Effect. To quoteFleming's own words:-

" In 1882, as Electrical Adviser to the Edison ElectricLight Company of London, I was brought into close touchwith the many problems of incandescent lamps and Ibegan to study the physical phenomena with all thescientific means at my disposal. Like everyone else, Inoticed that the filaments broke at the slightest shock, andwhen the lamps burned out the glass became discoloured.The discoloration of the glass was generally accepted asa matter of course. It seemed too trifling to notice.But in science it is the trifling things that count. The littlethings of today may develop into the great things oftomorrow. . . ."

467 ELECTRONIC ENGINEERING

The immediate objective, however, was to prolong thelife of the filaments and to prevent the carbon deposit.Edison himself was also working on the problem inAmerica, and tried various expedients to cure the trouble.He agreed with Fleming's findings, namely, that the depositconsisted of an accumulation of carbon atoms shot fromthe overheated point on the filament, and in one experi-ment introduced a coating of tinfoil inside the bulb, withthe object of applying a counter -charge of electricity tooff -set the bombardment. To Edison's surprise, when thefoil was connected, through a galvanometer, to thepositive leg of the filament, a small direct current registeredon the instrument. Connexion to the negative leg pro-duced no reading at all. Such, then, was the " EdisonEffect ".

This, to Edison, was a sidetrack (albeit a fascinatingone) to his main line of investigation, and he did notpursue it to the point of offering an explanation. Fleming,however, spent much time in research on the matter, andsubsequently gave lectures on his findings. These arouseda certain amount of interest in scientific circles, but causedno furore, as there appeared to be no practical applica-tion for the phenomenon.

For a time Fleming suspended his investigations, havingbeen appointed Professor of Electrical Engineering atUniversity College, London. He also subsequently becameexceptionally occupied in another direction, having under-taken, in 1899, the duties of technical consultant toMarconi's Wireless Telegraph Company.

One of his first assignments with Marconi's was a col-laboration with Marconi himself over the design of thetransmitter for Poldhu. This was terra incognita with avengeance, for all of Marconi's previous experiments hadbeen conducted with laboratory -type apparatus, whereasthe Trans -Atlantic project called for an engineeredtransmitter of high power. No previous data was there-fore available, of the design was headlinedin December 1901, when the Poldhu signals were pickedup in Newfoundland. Wireless had spanned the Atlantic-a feat which many of the eminent scientists of the timehad declared to be impossible. Fleming's part in theproject is suitably commemorated on the Poldhumemorial.

Wireless telegraphy of those days however, was handi-capped by one weak link. The most practicable detectorknown was the coherer, a form of relay which was, atbest, a temperamental and erratic performer. True, in1902, the Marconi magnetic detector appeared, and didsterling service for many years, but this had certain dis-advantages, not the least of which was a strong tendencyto be affected by static discharges. Many workers, amongthem Fleming, were seeking a sensitive and reliable meansof direct rectification of the high -frequency signals.

Fleming first approached the problem by experimentingwith chemical rectifiers, with no striking success. Then, inOctober 1904, he recalled his experiments with the Edisonlamps. Here was a device which, when the metal platewas given a positive potential with respect to the filament,would pass current, but would not do so when the platewas made negative. Might it not rectify wireless signals ?

Hastily fitting up a small spark transmitter at one endof his laboratory, Fleming resurrected one of his experi-mental lamps and wired it to a receiver in conjunctionwith a mirror galvanometer. Said Fleming, describingthe occasion:-

" It was about five o'clock in the evening when theapparatus was completed. I was, of course, most anxiousto test it without loss of time. We set the two circuits somedistance apart in the laboratory and I started the oscilla-tions in the primary circuit.

" To my delight I saw that the galvanometer indicated

a steady direct current passing through, and found thatwe had in this peculiar kind of electric lamp a solutionto the problem of rectifying high -frequency wirelesscurrents. The missing link in wireless was found-and itwas an electric lamp ! "

Fleming at once set to work improving the crude con-struction of his apparatus by making the metal plate intoa cylinder which enclosed the whole filament. The patent,filed on 16 November, 1904, described the apparatus subse-quently termed an " Oscillation Valve "; by this, of course,Fleming meant that it was a non -return valve for rectifyingoscillations.

Marconi, to whom Fleming wrote telling of his dis-covery, immediately foresaw at least some of itspossibilities. The Fleming valve was put into productionby Marconi's, and proved to be an unqualified success.

De Forest, in America, who had been closely followingFleming's work, conceived the idea of inserting a "grid"between filament and plate, whereby the electron flowmight be controlled. He found that under suitable con-ditions of operation small variations in P.D. between thegrid and filament produced large changes in the currentflowing between filament and plate; in short, amplificationof a signal could be effected.

De Forest's patent for this was at once challenged inthe U.S.A. by Marconi and in several important legalactions it was established that the principle involved in theFleming patent was fundamental, that it had priority andthat the grid was merely an improvement upon the basicidea.

Fleming was to live to see much of the fruits of hislabours, and to receive due honours, among them theGold Albert Medal-the ultimate award of the RoyalSociety of Arts-the Faraday Medal of the Institution ofElectrical Engineers, the Kelvin Medal and the FranklinMedal. In 1929 he was knighted for his valuable servicein science and industry. Far from resting on his laurelsafter 1904, he was active almost to the last-investigating,inventing, writing, lecturing. In his capacity as Professorof Electrical Engineering at University College, manyhundreds of radio engineers were trained by him, whilehis lectures achieved international fame. Many stillremember his Marconi Memorial lecture to the R.S.A. in1937 (given when he was 88), as a truly remarkabletour de force. His books, too, were classics of their kind.To mention only two: " The Principles of Electric WaveTelegraphy " (1906) was a standard work of reference toinnumerable wireless engineers for many years after, whilehis "Fifty Years of Electricity" (1921) makes fascinatingreading, and serves to give some idea of the ramificationsof Fleming's genius.

On the writer's desk is a letter written by Sir Ambrosein 1943. The handwriting is bold and vigorous, the mindbehind it obviously crystal-clear. In the course of theletter he says regretfully:-" . . . all the pioneers are dead(Sir Ambrose was referring to the original engineers ofthe Marconi Company)-Marconi, Jameson Davis, Kemp,Bradfield and possibly Paget. I am ninety-four years oldand have outlived them all, or nearly all . . . " He thenproceeds to write twenty-two pages of foolscap, whichdetails, with dates, various phases of the history of wire-less telegraphy from his own personal angle of scientificadviser to the company ! Nothing could be more charac-teristic of the enthusiasm and capacity for painstakingdetail which he carried with him throughout his life.

Two years later, on 18 April, 1945, Sir Ambrose Flemingdied, being in his ninety, -sixth year. So passed one ofthe giants of the Radio Age. Memorials to his fame arein almost every home in this country, and, indeed, through-out the world-the thermionic valves, which now formpart of our everyday life, and of which Fleming madethe first.


A Pulse -Interval Meterfor Measuring Pulse Repetition Frequency

(Part 1)By A. M. Andrew*, B.Sc., and T. D. M. Roberts*, B.Sc., Ph.D.

The type of counting -rate meter commonly used with Geiger counters is not suitable for indicatingpulse repetition frequency when the P.R.F. is changing rapidly and the indication is required to followthe variations accurately. Its limitations are serious in neurophysiological applications. An instru-ment is described which measures each pulse interval and provides an output voltage which is alinear function of the reciprocal of interval duration. The output voltage of the instrument at anyinstant is determined either by the duration of the preceding pulse interval, or by the durationwhich the current interval has already attained, whichever is the longer. In this way the instrumentgives a continuous indication of P.R.F. and responds to a change as rapidly as is physically possible.

ULSE repetition frequency (P.R.F.) can be indicatedP continuously by a counting -rate meter of the typefrequently used in conjunction with Geiger counters.Circuit techniques used in such meters have been reviewedby Smith'. For some purposes, however, such meters arenot satisfactory, for they incorporate an integrating circuitwhose time -constant is long compared with the durations ofthe intervals between pulses. They are therefore sluggishin their response to any change in P.R.F. which occurs in atime which is not extremely long compared with the pulseintervals.

In studying the discharges in nerve -fibres it is convenientto have an instrument which indicates and records the P.R.F.continuously. In this application the limitations of thecounting -rate meter are serious, for the P.R.F. may be quitelow and may change abruptly. We have therefore dev-lopedan instrument for indicating P.R.F. which responds imme-diately to a change in P.R.F. and yet gives a smooth outputwhen the P.R.F. is steady.

Messages are conveyed in nerves in the form of a suc-cession of " impulses ". Each impulse consists of a cycleof activity lasting about 1 millisecond. It is accompaniedby an electrical disturbance which can be detected throughsuitable electrodes and recorded. The impulses travel alongthe nerve -fibres at a velocity of a few metres per second.The interpretation by one part of the body of a messagecarried by a nerve from another part depends on the arrivalof impulses, on which nerve -fibres carry the impulses, andon how rapidly successive impulses follow one another.

A portion of a typical oscillograph record of impulses ina nerve -fibre is shown in Fig. 1. This particular record wasobtained from the nerve serving a sense -organ in the knee -joint of a cat. This sense -organ generates nerve -impulsesat a repetition frequency which has been found to dependon the angular position of the joint'. The second trace inthis record is used to indicate the angle of the joint; thesloping portion of this trace shows that the joint was movedduring this part of the record. The change in P.R.F. isclearly shown.

Most sense -organs which have been studied give rise todischarges of nerve impulses in a somewhat similar fashion.One difference between sense -organs which is of interestlies in the differing way in which the P.R.F. of the dischargechanges with changing conditions of stimulation of thesense -organ.

The instrument to be described has been developed tofacilitate the analysis of such changes in P.R.F. in the dis-charges from sense -organs and for studying discharges inother nerves. It may also prove to have applications inother fields.

The frequency range covered by the instrument is fromzero to 100 pulses/second, which is sufficient for most

" Institute of Physiology, University of Glasgow.

neurophysiological applications. No serious difficulty isanticipated in building a similar instrument to cover agreater range.

Principle of OperationEach interval between pulses is measured electronically

and determines an output voltage. The output voltage isan approximately linear function of the reciprocal of theinterval duration. Hence an oscilloscope or moving -coilmeter connected to the output of the pulse -interval meter

a

42 second

Fig. 1. Oscillograph record of impulses in a nerve -fibre coming from asense -organ in the knee -joint of a cat. Trace 1 shows the impulses. Trace2 is a simultaneous record of the angular position of the joint. Thesloping portion indicates that the joint is being moved at this stage inthe record

INCOMING PULSES

A

OUTPUTVOLTAGE

I I I I

TIME

F.g. 2. Incoming pulses and resulting output voltage where the outputvoltage at any instant is determined by the duration of the previous pulse -

interval

gives an indication of frequency on an approximately linearscale.

The series of output voltages determined by successiveintervals has to be combined to give a continuous indicationof frequency. A way in which this might have been doneis illustrated in Fig. 2. The instrument could have beendesigned so that the output voltage determined by eachinterval was given as output during the succeeding interval.In Fig. 2 the interval AB is short and therefore correspondsto a high frequency; hence the output voltage is high duringthe interval BC. The interval BC is longer and correspondsto a lower frequency, so the output voltage is lower duringCD, and so on. This mode of operation may be describedby saying that the output at any instant is determined bythe duration of the preceding pulse interval.

A serious disadvantage of an instrument operating as


described above would be that if the P.R.F. fell to zero theinstrument would not give an indication of zero frequency,but would continue indefinitely to indicate the frequencycorresponding to the duration of the interval between thelast two pulses. This property is illustrated at the right-hand end of Fig. 2.

The mode of operation actually employed is slightlydifferent. The output voltage at any instant is determinedeither by the duration of the preceding pulse -interval or bythe duration which the current interval has already attained;whichever is the longer. This mode of operation is illus-trated in Fig. 3. When the P.R.F. becomes zero the outputvoltage falls asymptotically towards the value correspond-ing to zero frequency.

Definition of FrequencyWhen pulses are occurring somewhat irregularly, the

most practical definition of frequency appears to be as thereciprocal of the interval between two successive pulses.Using this definition, the instrument responds to a changein frequency as rapidly as is physically possible. If aninterval is shorter than the preceding one the higher valuefor the frequency is indicated as soon as the interval iscompleted. If an interval is longer than the preceding onethe instrument does not wait until the end of the intervalbefore indicating a reduction in frequency. For instance,in Fig. 3 the indication begins to fall away at 13', where

Each timing unit includes a means of charging its capa-citor in the manner described and also a means of discharg-ing it. The timing units are connected to the changeovercircuit in such a way that charging and discharging canoccur only in that timing unit which is currently operativein measuring a pulse -interval. Furthermore, dischargingcan occur only while the resetter phantastron is in its quasi -stable state.

INCOMING

I

A B i0

OUTPUTVOLTAGE

I I I

TIME

Fig. 3. Incoming pulses and resulting output voltage of the pulse -intervalmeter

MonitOotport

Input

I - II. J,AMPLITUDE

DISCRIMINATOR

r i

Clog S

I .

dIII

BB' = AB.

Arrangement of the InstrumentFig.,4 shows a block diagram of the instrument, with

associated waveforms. The incoming pulses are applied toan amplitude discriminator, which is triggered only bypulses of greater than a certain amplitude. Pulses from thediscriminator then reach a gate circuit, which is closed to

CATE

I ;

1CHANGEOVER

CIRCUIT

further pulses for a time after a pulse has passed through. RE EEEEEEPHANTASTRON

The moment of reopening of the gate is controlled fromfurther on in the circuit. Its purpose will be discussed later. 1-- -

The timing of the pulse intervals is done by two timing SWITCHED

units which come into play alternately. To produce thealternate operation, pulses which come through the gateare made to operate a " changeover circuit " which consists

CHRCUINGCIRCUIT

Chorgi

Discharging,SWITCHED

DISCHARGINGCIRCUIT

of an Eccles -Jordan trigger circuit or bistable multi -vibrator". Of the two outputs which are taken from thiscircuit one is always positive and one negative, and theychange over every time a pulse comes through the gate.

Timing UnitA

Chong ingiSWITCHEDCHARGING

cUITEach timing unit has two possible states during any pulse -

interval; it may operate to "measure" the pulse -intervalDischarg ing

or it may hold the capacitor charge which represents a 5W ITCHEDDISCHARGING

CIRCUITmeasure of the duration of the previous interval. Duringeach interval a capacitor is charged in whichever timingunit is operative, and the voltage which it reaches dependson the duration of the interval. The capacitor is charged

.010UnitTimng

in such a way that, except during the first 1 /100sec of theinterval, the voltage at any instant differs from a certainfixed voltage by an amount which is inversely proportional

SELECTOR OFMORE POSITIVE

VOLTAGE

to the time which has elapsed since the start of the interval. OUTPUT OUTPUT

Thus if V is the voltage reached, and the last pulse occurredat time t = 0:

TO METER TO RECORDERquencis,Frecaly'

S \ rr170 - = /Or for t > 1 /100 (1)

where k and Y. are constants.It is clear that the charging process cannot conform to

equation (1) from t = 0, for when t = 0, V would have totake the value of minus infinity. Instead, the capacitor isnot allowed to start charging until a time of just over 7msechas elapsed since the occurrence of a pulse. For values oft greater than 10msec the charging process conforms toequation (1).

The delay of approximately 7msec is adjusted to thecorrect value by a procedure which will be described. Thedelay is introduced by the two circuits termed " delayphantastron " and " resetter phantastron," of which thedelay phantastron introduces about Imsec delay and theresetter phantastron the remainder.

CurrentOutput

Vol topOutput

Fig. 4. Block diagram with associated waveforms

The cycle of operations in the timing units may be seenfrom the waveforms of Fig. 4. At the occurrence of apulse, that timing unit which was previously in the" holding " state changes over. Charging of the capacitorcommences, but only proceeds for lmsec before the resetterphantastron is flipped and discharging takes place. Thecapacitor is held discharged until the resetter phantastronflops and the capacitor is then charged as described above.The initial rise of voltage during the lmsec delay time isan undesired effect, but it is not serious as the rise is slight.

When the timing unit changes over to the " holding "


state, charging of the capacitor ceases, and the capacitorneither gains nor loses charge during the next pulse interval.

The voltages developed across the capacitors of the timingunits are combined to give the output voltage of the instru-ment by the circuit termed " selector of more positivevoltage ". This arrangement gives the mode of operationillustrated in Fig. 3. Had it been desired to make aninstrument operating as illustrated in Fig. 2, the selectorof more positive voltage would have been replaced by anelectronic switch so arranged that the output voltage wasderived from whichever of the timing units was in the" holding " state. The output voltage of the selector of morepositive voltage is effectively the output voltage of theinstrument.

The output voltage becomes more positive with increas-ing interval -duration and hence more negative withincreasing frequency. The inverted waveform at the footof Fig. 4, where the frequency -scale increases in an upwarddirection, does not occur in the instrument, but the outputis normally connected to a pen -recorder amplifier in such away that an increase. in pulse -frequency causes upwarddeflexion of the pen.

PURPOSE OF DELAY PHANTASTRONThe delay phantastron is included for two reasons. It is

necessary that the changeover circuit should have changedover before the discharging process is initiated by theresetter phantastron, otherwise the wrong timing capacitormay be partially discharged. The inclusion of the delayphantastron ensures that the changeover definitely precedesthe discharging.

The second reason for including the delay phantastron isthat it and the gate ensure that the resetter phantastron cannever under any circumstances be triggered until at leastlmsec has elapsed since it flopped to its stable state afterthe previous operation. The gate does not open, and hencethe delay phantastron cannot be triggered, until the resetterphantastron returns to its stable state. The phantastron,like all trigger circuits, requires a certain recovery timebetween operations. If it is not given sufficient time in whichto recover, the duration of its stay in the quasi -stable stateis reduced.

PURPOSE OF THE GATEThe gate ensures that neither the delay phantastron nor

the resetter phantastron is re -triggered until it has had anadequate recovery time. The arrangement is such that thesetwo phantastrons are triggered alternately, and each alwayshas a recovery time which is at least equal to the durationof the quasi -stable state of the other. The gate also ensuresthat only those pulses which are effective in triggeringthe two phantastrons get through to the changeover circuit.

The gate has no effect on the operation of the instrumentexcept when two incoming pulses are separated by less thanabout 7msec. If the gate were not included it would bedifficult to predict the response of the instrument underthese conditions, because the phantastrons might be trig-gered after an insufficient recovery time, and the change-over circuit might be changed over although the resetterphantastron was not ready for re -triggering. With thearrangement used, the second pulse is rejected by the gate,and an overload of the instrument by too high an inputfrequency leads simply to frequency division; which startsto occur at about 140p/ s. An input frequency of 150p/sleads to an output voltage corresponding to 75p/s.

Circuit DetailsThe complete circuit is shown in Figs. 5, 6 and 8.

AMPLITUDE DISCRIMINATORThe incoming pulses are amplified by V1, the anode of

which is connected through an RC coupling to the grid ofthe cathode -follower V21. The cathode of V,a goes to Vwhich is connected as a Schmitt trigger circuit, or cathode -

coupled bistable multivibrator.4 This acts as a squaringcircuit whose output is differentiated, and the resulting nega-tive pulses are applied to V2b and to V5, which is part of thegate circuit.

When the polarity selector switch is in the positive pulseposition, the grid leak R, is taken to a standing voltagesuch that the mean potential of V2a cathode is more posi-tive than the critical voltage range of the Schmitt trigger.Thus to operate the Schmitt trigger, a negative pulse isrequired at the anode of V,. With the switch in this posi-tion, therefore, the instrument responds to positive pulsesat the grid of V,. Conversely, when the polarity selectorswitch is in the negative pulse position, the grid leak R2is taken to a standing voltage such that the mean potentialof V2a cathode is more negative than the critical voltagerange of the Schmitt trigger. The instrument then respondsto negative pulses at the grid of V,. The central test posi-tion of the polarity selector switch is only used whenadjusting the preset variable resistor VR as described later.

The cathode -follower V2a, is included to ensure that thecoupling capacitor does not receive charge when Vaa passesgrid current. R, is included to limit the grid current ofV,a, since without this stopper resistor the grid current canbe so large as to interfere with the action of the Schmitttrigger. The speeding -up capacitor C, is of a very smallvalue, for with larger values the Schmitt trigger circuit cango into oscillation when Vaa grid voltage falls in a certainrange. This oscillation would not matter if the input alwaysconsisted of short pulses, but it could be troublesome whencalibrating with a low -frequency sinusoidal input.

The " accepted pulses " from the amplitude discriminatorgo through the cathode -follower V2b to the monitor output.This is usually connected to a headphone or through anamplifier to a loudspeaker, and it is then useful when adjust-ing the gain control so that the Schmitt trigger is triggeredonly by the wanted pulses.

GATEThe gate is required to remain closed, after a pulse has

passed through it, until the resetter phantastron flops fromits quasi -stable state back to its stable state. The gate circuitincludes V5, V6 and V,. V. and V, form a flip-flop ormonostable multivibrator in which V5 is normally conduct-ing and V, normally cut off. A negative pulse applied tog, of V. flips the circuit to the quasi -stable state whereinV, conducts and V. is cut off. Differentiating circuits areconnected to anode and screen of V so the commence-ment of current in V, gives rise to negative output pulseswhich trigger the delay phantastron and the changeovercircuit. While the gate circuit remains in its quasi -stablestate no further pulses can come from it; the gate is closed.After a millisecond the resetter phantastron is flipped toits quasi -stable state and V6 starts to conduct. The voltagedrop across the common anode load of V5 and V, cuts offV,. V, cannot conduct until the resetter phantastron flopsback to its stable state. As soon as the resetter phantastronflops back, V, becomes cut off and the gate is immediatelyready to respond to the next incoming pulse from theamplitude discriminator.

The time -constant R,C, plays no part in timing the abovecycle of events, for the monostable multivibrator formedby V5 and V; is not allowed to flop to its stable state of itsown accord. It is made to return to it when V, conducts.The circuit would work if R, and C2 were replaced by adirect coupling, so that V. and V; formed a bistable multi -vibrator. With the bistable arrangement, however, thecircuit might, on switching on, go into the state where V,conducts and V., is cut off, and it would remain that wayindefinitely, with no pulses passing through the gate. Themonostable circuit is therefore preferred.DELAY AND RESETTER PHANTASTRONS

Miller-transitron circuits, or monostable screen -coupledphantastrons5 have been used, because this type of circuit


350V

250V

100k

47 0

40

VR

22M

033

0k0

10k

0

1501

8022

0k0

68k0

613k

0lO

OkO

R.,

100k

047

M0

47M

033

0k0

C2

47k0

H6

47k0

Sf 310

0180

100

'Pa? C)+

470k

050

0pF

-002

µFV

V,O

.V

b10

0k0

VP

b

*-- 4

7M0

VII

1,i.

.F+

Ye

II10

0>F

IMO

MO

IMO

025µ

Fpu

lses

RV

Vat

C,

2b

6H6

-V

It1

V'''

V

2-2M

0...

Ma

mi.

100p

F33

0pF

---y

eo22

k0 p

ulse

s--

- -

_-

-,

---

,47

0 kr

)66

N7

- -

- -

,T

_,...

..,--

-P

olar

ityk.

..../

., \-_-

J,,t

7j..

200p

e,^,

...--

50pF

1

ISO

OpF

CA

F32

.I.

50pF

.=\

\.._.

.../

22k0

Sel

ecto

rE

F50

EF

500

EF

50Iµ

FS

witc

h

R2

o65

N7 43

47k0

65N

744

EF

50E

F50

V4b

6F32

VI3

13V

I4

330I

c033

0kC

V

2-2M

0V

R1

220k

022

k022

0k0

L6

"-^. H

6IM

0

.....

470k

022

0k0

EA

5047

0k0

1110

0rF

1.47

k0 y

5tF

Ok0

Mon

.s

_10

0k0

100k

0

t pi L

ott-

i 0.1µ

FC

7R

sal

pF-, __

I50V

1

1001

8010

0k0

EF

5047

01(0

100k

0V

ie EA

50

R6

IMO

2201

(068

0k0

6130

40

L2

0Y

INP

UT

AM

PLI

FIE

RA

MP

LIT

UD

E D

ISC

RIM

INA

TO

RG

AT

ED

ELA

Y P

HA

NT

AS

TR

ON

RE

SE

TT

ER

PH

AN

TA

ST

RO

N

350V ®

i Plu

g-in

uni

tfo

r S

ingl

e -D

ude

!App

roxi

mat

ion

6SN

7

R,

h55M

0tr

ioP

K,

1-65

mo

/491

16k0

1 106

63V

50c.

/s22

k0

E7

2 80k0

2-2M

0

65L7

V 3

8

470k

0

Met

erIM

OIM

OS

hift

Zer

oS

et

C7

...cy

ospr

C5

...0.

051.

S

T*-

I$T

±1%

1V,

..\V

,.47

01(0

4701

(06

--'\.

/bA

t-10

01(0

r jE

CC

35

100k

0

-150

V

SW

ITC

HE

D C

HA

RG

ING

' CIR

CU

ITS

A

EF

50

-V

2

c.-:

2NE

F50

EF

50

-C

P

> R

w47

060

s

150k

0

SW

ITC

HE

D D

ISC

HA

RG

ING

CIR

CU

ITS

PO

SIT

IVER

OF

LIII

AA

OG

RE

E

v244

65N

7 V

248

(1.7

>25

k0

met

er, r

eadi

ng0-

100.

1.

Jock

for

0-50

0µ A

Met

er,

3960

sens

itivi

ty

I M.0

680k

0

> 6

8k0

OU

TP

UT

VA

LVE

S

NA

,

Vn

Hea

ter

Cat

hode

6.3V

06A

6860

V10

Hea

ter

6-3V

04A

6.3V

50c/

s

Cat

hode

Va

CH

AN

GE

OV

ER

CIR

CU

IT

Fig.

5.

Cir

cuit

diag

ram

is noted for the stability of its timing. The delay phantas-tron is triggered by a negative pulse applied through Vga,and the delayed negative output pulse is obtained bydifferentiating the waveform at the screen of V9. Thearrangement of two diodes Vio. and Viol) is needed toeliminate the positive pulse produced when the phantastronis triggered.

The negative pulse from the delay phantastron triggersthe resetter phantastron V13. The duration of the quasi -stable state of the resetter is adjustable by the presetresistor VR2. A cathode -follower Vila is incorporated toensure that the resetter is ready for re -triggering after ashort recovery time (see reference 5). This refinement isnot needed in the delay phantastron, where the recovery isalways several times the duration of the quasi -stable state.

The waveform on the suppressor of V is a positive -going rectangle. It is coupled to the grids of V, and V21,so that these valves, which are normally cut off, conductduring the quasi -stable state of the resetter. The waveformat the suppressor is preferred to that at the screen becauseit has a flatter top, being clipped by V14. The cathode -follower Vb is inserted to isolate V from effects ofcurrent in V12 or grid current in V, and V21. C, and R6couple the cathode of V11b to the grids of V, and V21. V12acts as a D.C. restorer and R5 is included to limit grid currentin V, and V21.

CHANGEOVER CIRCUITThis has two stable states, one with V conducting and

V15 cut off, and the other with V1, cut off and V con-ducting. The application of a short negative pulse to thesuppressors causes the circuit to change from whicheverstate it is in to the other. The mechanism of the change-over is fully described by Puckle3. The two outputs ofthe circuit are labelled A and B. When V5 conducts and V16is cut off, A is positive and B negative with respect to theirmean potential, and vice versa when V1. is cut off and V16conducts.

TIMING UNITSThe two timing units are not, in fact, completely indepen-

dent as shown in the block diagram (Fig. 4). The twocapacitors are C, and C Consider first the charging anddischarging of C4. It is charged by the combined anodeand grid currents of Vb. The charging occurs only whenVisa is cut off, for when V, conducts, VID is cut off.C, is discharged when V2 and V21 conduct, and then Va,connected as a diode, prevents the live side of the capa-citor from being taken below earth potential.

When A is positive and B negative, the left-hand timingunit (incorporating C4) is operative in "measuring" a pulse -interval, for Vb is conducting, and V is also ready toconduct during the time when V21 conducts. The right-hand timing unit is then holding the charge on C forV,, and V are both non -conducting. When B is positiveand A negative the conditions are reversed.

The instrument is designed to indicate frequency on anapproximately linear scale over the range 0 to 100p/s. It istherefore necessary that the voltage of the capacitor inthe operative timing unit should conform closely to equa-tion (1) after the first 1/100sec of the interval. In the prac-tical instrument Va=250 volts, for the capacitor chargestowards the 250 volt H.T. line. The circuit is so designedand adjusted (by adjustment of VR..) that when t =-1/100sec, V = 50 volts. Thus equation (1) becomes :

250 -V = 2/t (2)

and the charging process must approximate to this for> 1/100.A rough approximation to the required charging law can

be made by using the circuit of Fig. 7(a). When the switchS is opened the capacitor will be charged through both R,and R9, until the voltage across it reaches a value Va givenby:

V, = VaRill(Ria + RH) (3)

Once this voltage is reached, no more charge is receivedthrough R and the capacitor is charged only through R7.

The charging curve is made up of two exponential curves,one of which is followed from V= 0 to V = Ve, and theother from V = Va to V == V9. By a suitable choice ofresistance values, the composite curve can be made toapproximate the curve represented by equation (2), (seeAppendix A). The timing units of the pulse -interval meter

Fig. 6. Plug-in unit for the 5 -diode approximation to the required charginglaw. All resistance values are plus or minus 1 per cent

(0)

(c)Fig. 7(a). Circuit giving single -diode approximation to the required charging

law(b) Circuit giving 5 -diode approximation

(c) Practical circuit giving 5 -diode approximation

incorporate an arrangement which is effectively that of Fig.7(a). In the left-hand timing unit the triode Vb takes theplace of the diode in Fig. 7(a). Resistors R9, R and R.are common to the two timing units. R instead of beingconnected directly to the capacitor, goes to the grid of V17b.

The arrangement shown in Fig. 5 and operating asdescribed above gives what is termed a single -diode approxi-mation to the required charging law. A closer approxima-tion can be obtained by using more diodes, as shown inFig. 7(b), with resistance values chosen so that the diodecurrents are successively cut off at different voltages. A


11

practical circuit for our purpose is shown in Fig. 7(c) andis considered in greater detail in Appendix B. The plug-inunit shown in Fig. 5 can be replaced by the more complexunit shown in Fig. 6, to give a five -diode approximation tothe required law.

The pulse -interval meter is normally operated with thismore complex plug-in unit. The relationship between outputvoltage and applied pulse -frequency is then very nearlylinear. The simpler plug-in unit is shown in Fig. 5 forsimplicity, and also because its closeness of approximationto the required law is remarkably good, considering itssimplicity. (See Figs. 14(a) and 14(b) ).

Alternative plug-in units can be devised to give non-linear frequency scales, if required. (See Appendix C).SELECTOR OF MORE POSITIVE VOLTAGE

This consists of the two cathode -follower valves V,and V23b with a common cathode resistor. The cathodepotential is determined almost entirely by the morepositive grid. When the difference in grid potentials ismore than a few volts, the more negative grid has no effectwhatever, since the valve to which it belongs is cut off.When the grid potentials are closer the more negative onehas some effect, but it can only alter the cathode potentialby a fraction of a volt at the most.

OUTPUT STAGESThe voltage variations at V23 cathode constitute the out-

put of the instrument. A fraction of the variation is tappedoff at the junction of R12 and R13, and the same fraction atR, -R,5 junction, so that shift controls can be introduced.The shift control for the current output is termed " meterzero set " and is used for that purpose.

V245 and V20 are cathode -follower output valves for thevoltage and current outputs respectively. The current out-put is of suitable magnitude for connexion to a 0 to 500µAmeter. The excursion of output voltage for the frequencyrange of 0 to 100p/ s, with the output voltage control turnedright up, is just over 6 volts, and it can be adjusted to swingequal amounts positive and negative with respect to earth.

REFERENCES

1. SMITH G. D. Counting -rate Meters. Electronic Engng. 24, 141(1952).2. BOYD, I. A., ROBERTS, T. D. M. Proprioceptive Discharges from Stretch -

Receptors in the Knee -Joint of the Cat. J. Physiology 122, 38 (1953).3. PUCKLE, 0. S. Time Bases, 2nd Ed., p. 76 (London, Chapman & Hall Ltd.,

1952).4. CHANCE, B., HUGHES, V. W., MACNICHOL, E. F., SAYRE, D., WILLIAMS, F. C.

Waveforms p. 164. (New York, McGraw-Hill Book Co., Inc., 1949).5. CHANCE, B. et al. Waveforms, p. 197.

(To be continued)

New G.E.C. Laboratories for Semiconductor Research and DevelopmentANEW two -storey extension has recently been added to the

General Electric Company's research laboratories andwill be given over to semiconductor research and development.

Future plans provide for still further expansion in this fieldof research. A brief outline of the work on which the variousdepartments are engaged is given below.

Basic Research in Solid PhysicsKnown semiconductors such as germanium and silicon have

physical properties (such as energy gap and charge carrier. mobilities) which are not ideally balanced for use in some

devices. It is possible to envisage materials with more desir-able properties and which would be neither so rare nordifficult to prepare as the semiconductors used at present. Thelaboratories are making and investigating the properties ofsuch materials, including a new group of compounds with acrystal structure closely related to that of silicon andgermanium. Known as chalcopyrite type materials, they havealready been shown to possess interesting semiconductingproperties. For example, copper indium selenide (CuInSe0has shown point contact rectification with peak inversevoltages of about 400 volts.

The second purpose of research into new materials is togive greater insight into the physical properties of semi-conductors. This field is relatively undeveloped but alreadymany unusual effects, thermal, optical and magnetic, as wellas electrical, have been discovered. An investigation into thethermo-electric effects in semiconductors is just one part of aprogramme to elucidate some of these unusual properties.The magnitude of the effect is, however, very small if con-ventional metals are used. Some semiconductors show a farmore favourable combination of properties and it was possibleto choose, out of the large number recently prepared, theparticular material which would be expected on theoreticalgrounds to give the best performance. The junction of themetal bismuth and the new semiconductor bismuth telluridecan be used to produce a temperature difference of 26°C, andwork on other materials is proceeding with a view to obtain-ing even greater effects.

Fundamental studies have shown that a knowledge of thebulk properties is not sufficient for solving application prob-lems. Every specimen is necessarily limited by a surface which,in an actual device, may be exposed to atmosphere or joinedto another surface. The phenomena occurring at the surfaceof a semiconductor are in fact radically different from thosein the bulk material. Even with silicon and germanium, thepresent understanding of the surface phenomena is incomplete,

and this is even truer of the new semiconductors.The effect of various surface treatments on the electrical

properties of these materials is being studied. For example.the bombardment of a silicon surface with ions of variousgases accelerated by an applied potential of 30 OQO voltsproduces a drastic change in the electrical properties. A com-parison between the current -voltage characteristics of thetreated and untreated materials shows that the ion bombard-ment produces a permanent improvement in the rectifyingeffect.

Semiconductor MaterialsThe problems concerned in the preparation of suitable semi-

conductor materials can perhaps best be illustrated by refer-ence to germanium. The material used by British manufac-turers of crystal valves is obtained from the dust and sootwhich collects in the flues of gas -works, particularly wherecoals from Northumberland and Durham are used. TheG.E.C. research laboratories carried out an extensive searchfor an indigenous source of germanium several years ago andas a result a substantial annual tonnage of germanium -bearing flue -dust is now available. The semiconductor, onceso rare as to be considered a chemical curiosity, is usuallypresent at 0.5-1.0 per cent by weight in the better flue -dustsand can now be obtained in quantities of the order, ofhundredweights.

After its extraction from the flue -dust, germanium is givenelaborate chemical purification and is supplied to thelaboratories as germanium dioxide, which is then reducedby high temperature treatment with hydrogen. The metalthus obtained is fused and cast into an ingot, which has aboutone part of impurity to every 10 million parts of germanium.Although very pure by chemical standards, this is still almosta hundred times as impure as required for semiconductordevices.

The necessary further purification is accomplished by meansof a directional freezing technique known as zone refining.Only a small region of the ingot is melted at any one time,but the heat source is moved so that the molten zone alsomoves and slowly traverses the length of the bar. During theprocess impurities, when at the junction of liquid and solid,are concentrating preferentially in the liquid zone. Byrepeatedly traversing the bar, therefore, the impurities areultimately swept to one end of the ingot, which is thensawn off.

Having obtained germanium of suitable purity, it thenbecomes necessary to prepare it in the form of a single crystal


so as to give the required electrical properties. The metal isagain melted, this time in a crucible, and a minute controlledamount of the element which determines the electrical pro-perties is added. A small " seed " of monocrystallinegermanium is dipped into the molten mixture and, with veryprecise temperature control, the germanium begins to depositin solid form on the " seed ". By withdrawing the growingcrystal at a predetermined rate, the entire contents of thecrucible can be made to solidify in the form of a mono -crystalline ingot.

Semiconductor DevicesWith the materials available, the device designer has to

develop new circuit elements that will meet the needs ofindustry. The early work on the design and production ofpoint contact silicon crystal diodes for high -frequency mixerwork is well known. Now, after a period in which the mainemphasis has been on germanium devices, attention is againbeing focused on the use of silicon. Preliminary studies haveindicated that silicon p -n junction diodes have several usefulcharacteristics including the ability to operate at considerablyhigher ambient temperatures than their germanium counter-parts, very low inverse currents and a large rectification ratiobetween forward and reverse currents. To prepare silicon p -njunctions donor and acceptor type electrodes are attached toa homogeneous silicon crystal of either type by heating thecrystal and then bringing it into contact with metals to which

Purification of germanium by zone refining. The germanium ingot isplaced in a graphite crucible and the zone is melted by eddy current heating

it will alloy. A junction with p -type silicon, for instance, ismade with a donor metal or an alloy containing a donorelement such as antimony, phosphorus or arsenic. The junc-tion is grown by deposition from the molten alloy when cooledand is situated between the unmelted silicon and the metalsolid solution. An ohmic or base contact can be formed inthe same way except that, on p -type silicon for example, anacceptor element such as aluminium or indium is used. Bycareful control of the heating and cooling cycle, and theselection of suitable metals and alloys, both the junction andthe base contact can be formed simultaneously.

In one of the techniques being used, a gold -antimony alloywire forms a p -n junction on p -type silicon and an aluminiumwire provides the base contact. With n -type silicon these roleswould be reversed, but no changes would be required in themanufacturing technique.

One of the rectifiers now being developed has a fairlymassive copper base to remove heat dissipated in the device.When the p -n junction has been made, an enclosing coppercap is hermetically sealed to this base by a cold pressurewelding technique. The success of this sealing method is suchthat these units have withstood long periods of storage undersevere " jungle " conditions without change of characteristics.

Typical characteristics of one of the present designs of

rectifier are 10A at 0.5V, and lmA at -30V and 10mA at-160V.Semiconductor Electronics

The main uses of the present semiconductor devices are inelectronic equipments where small size, light weight, long life,ruggedness, reliability and low power consumption are impor-tant considerations. Much work is therefore being done in thedesign of suitable circuits for use with crystal valves and onthe determination of the basic principles of their operation.

Crystal valves are at present limited in their range ofapplication by their maximum frequency of operation andtheir power output, readily available types being usable onlyup to frequencies of about 500kc/s with output powers of afraction of a watt. These limits are, however, being rapidlyextended by improvements in design and the development ofnew types. Experimental types have already been establishedwhich are capable of operating up to 10 or 20Mc/s as ampli-fiers and up to 100Mc/s as oscillators, while others workingin the audio frequency range are capable of giving severalwatts output.

The most immediate and most significant of applications forcrystal valves are likely to fall in the telecommunications field,where their special properties provide the solutions to exist-ing problems in equipment design and open up quite newpossibilities for the future. For example, crystal valves arelikely in future to be found at many points in telephone

This weather -dependent alarm clock is being developed as an illustration ofthe uses to which semi -conductor devices can be put. It incorporates alight-sensitive germanium junction photocell with two point -contacttransistors as amplifiers. The alarm sounds only if a pre-set brightness

level is obtained.

systems; in exchanges, repeaters and subscribers' equipment.Many of the circuit problems involved are common also tocomputors and calculating machines, so that the establish-ment of a sound design for the elementary " bricks " of thesystem will lay a foundation for a far wider range of applica-tion.

As far as domestic radio and television receivers are con-cerned, the earliest use of crystal valves is likely to be inpersonal or small portable radio receivers, which will giveperformances equal to present valve receivers but will requireonly 1/10th the power.

At the present state of development the study of deviceapplication falls naturally into three stages :-

(a) The measurement and study of the characteristics ofdevices under development in order to providedetailed information and specifications to users.

(b) The study of the basic problems inherent in designingelectric circuits round the devices.

(c) The application of the devices to actual equipmentproblems.


Differential Width Control for TelevisionLine Scanning Circuits

By K. G. Beauchamp*, A.M.Brit.I.R.E.

Methods of width control in television receiver scanning circuits are discussed and design tech-niques evolved for a differential type of width control. Particular consideration is given to re-duction of the variation in E.H.T. developed by the scanning circuit as the picture width is varied.

The causes of these variations are investigated and means suggested for overcoming them.

MHE literature appertaining to television line scanning1 circuits is fairly extensive and in particular the mode

and theory of operation of resonant return or efficiencydiode circuits has been fully dealt with elsewhere"2,2.'.However, as far as the author is aware, no detailed attemptshave been made to analyse the methods by which theamplitude of the sawtooth current waveform generatedcan be made to vary without at the same time unduly affect-ing the E.H.T., which, in the majority of domestic televisionreceivers, is derived from the line scanning circuit.

Methods of Varying the Scan AmplitudeA typical line scanning circuit is shown in Fig. 1(a). Here

V, with T, and associated circuits form a blocking oscil-lator supplying a positive -going sawtooth voltage to thegrid of V,. The amplitude of this waveform is such as torender V2 non-conductive during almost half the total scan-ning period, while the efficiency diode V, is conducting.The action of these two valves can be loosely consideredas a push-pull arrangement supplying a sawtooth of currentto the scanning coils L, via a coupling transformer T2.

A high potential pulse voltage is present across the auto -transformer during the retrace period and may be increasedin value by an additional winding 5-6. The amplified pulsevoltage may, after rectification by V be applied to thecathode-ray tube anode terminal as accelerating potential(E.H.T.).

This is a simplified circuit with such components as gridstoppers, linearity controls, etc., omitted for clarity.

Study of this circuit will reveal a number of ways inwhich the sawtooth current, i, may be varied. Several ofthese are shown in Fig. 1(b) and will now be examined inthe light of their effect on the magnitude of the voltagepulse (v), appearing at V2 anode during the retrace period.

This potential has been given elsewhere' as :v = e-089/Qr . I . V(L/C) volts (1)

where := Q of resonant circuit during retrace period.

I = Maximum value of V2 anode current.L = Total inductance at anode of V2.C = Total capacitance at V2 anode.

Any control of the input waveform supplied to V2 gridby variation of C or R, will vary the pentode anode currentand hence v. In addition, variation of the charging capa-citor C, will have the undesirable effect of varying theoperating frequency of the oscillator V,. Similarly, varia-tion of screen -grid potential by R, or cathode bias by Ra(with or without negative feedback by choice of C, value)will affect V., anode current and hence peak potential v.Alteration of the H.T. supply by R, or boosted H.T. by R4,will also exert control over I, but will have an advantageover the preceding four methods in that the linearity of the

G.E.C. Development Laboratories, Coventry.

scanning waveform is less likely to be affected with changesof picture width.

All the preceding methods, however, give a poor ratio ofscan variation to E.H.T. change, as reference to equation

T( a)

(b)

KT.

EH o

r -

Fig. 1(a). Simplified line scanning circuit. (b) As (a) with possible widthcontrols added

(1) will show the E.H.T. changes linearly with change ofpeak anode current I.

An improved method is to vary the matching of thescanning coils Ly to that of the output valve V2. This canbe achieved by either a series inductance La, or an induct-ance L, in parallel with part of the transformer winding.

Both these methods can be shown to be equivalent tovariation of Ly and hence the total inductance L of equa-tion (1). The effect of the E.H.T. generated is, however,less as v is proportional to the square root of L. One dis-advantage of varying L is that in doing so the transformerefficiency may be considerably reduced. An expression for


this is given by Friend' in terms of deflexion factor Fa:k

1 + IL,_,Yoke ampere -turns for a practical transformerYoke ampere -turns for an ideal transformer

(2)where L1, = Inductance of transformer scanning coil wind-

ing 1-3.k = Transformer coupling factor.

Reduction in transformer efficiency due to this cause resultsin an increase in is and anode dissipation for V2, both ofwhich limit the maximum power that may be safely handledby this valve.

It is possible, however, to use a combination of the twoinductive methods of scan control by arranging that as L.is increased in value, so L, is decreased; the rates of induct-ance change in both cases being such that the totalinductance across the transformer windings 1-3 remainsconstant. Thus only the sensitivity of the scanning coils isaffected, allowing L in equation (1) to remain constant.

This method is known as the differential method ofwidth control and the remainder of this article will dealwith the calculation and design of suitable systems of thistype and an evaluation of their relative performance.

Criterion of PerformanceIn assessing the performance of a width control system

one is interested in obtaining an adequate variation ofpicture width to compensate for changes occuring bothduring the life of the receiver, and by the manufacturer, tocover expected production tolerances. A figure of +10 percent variation about the mean scan width is generally desir-able and should give sufficient compensation. Also, as hasbeen previously mentioned, as little variation of E.H.T. aspossible is required during the adjustment of picture width.

Consequently one can establish a figure of merit for awidth control system as:

=Maximum change of scan width

KMinimum change of E.H.T. (3)

It is also desirable that K remain constant throughout theentire range of the control.

Obtaining Maximum Change of Scan WidthThe simplest arrangement for the width coils is to use a

long solenoid through which passes an adjustable core. Anapproximate inductance formula for such a coil is given as:

47122}1µL=109/

where A = cross-sectional area of coil, cm2/ = length of coil, cm

u = permeability of core.Therefore a long solenoid of small cross-sectional area isnecessary with an adjustable core of high permeabilitymaterial. In practice it will be found that the coil lengthwill be controlled by the length of the core chosen; noadvantage being derived from using a coil of greater lengththan the core.

A suitable diameter for the coils used lies around 0.25in.This enables a long coil of suitable inductance to be woundand readily available core materials used.

Using two such solenoids L L wound on the sameformer as shown in Fig. 2 it is possible, by movement ofcore C, to arrange that their inductances will have theinverse relationship required in a differential width system.

Henries (4)

Choice of Core MaterialThe factor mainly required from the core material used

is high incremental permeability at the band of frequenciesassociated with the line scanning circuit (approximately 10to 100kc/s). As will be seen later, eddy current andhysteresis losses play some part in the performance of thewidth coil as it is desirable to keep the Q of the coil rela-tively constant.

Three types of core material appear possible:(1) A laminated silicon iron core (i.e. a bundle of iron

wires bonded together with an insulating medium).(2) An Iron -dust core.(3) A Ferrite core.The core losses with the laminated iron at the frequencies

involved render it unattractive for this purpose and a prac-tical choice lies between iron -dust and ferrite core materials.

Due to the small size of the dust -iron particles(< 50 microns diameter) and the relatively large mass ofinsulating medium surrounding them, incremental perme-abilities of only about 4 to 6 are possible, although corelosses are very small.

Using ferrite cores' the losses are negligible and due toits homogenous nature incremental permeabilities of 7 to10 may be realized. Rods of ferrite material are availablein extruded form and prove very useful for this application.

T2

L, L,

d

0

Fig. 2. Coil arrangement of a differential width system

(a)

Fig. 3. Circuit arrangementlb)

Design of a Differential SystemThe part of the line scanning circuit involving the width

system is shown in Fig. 3(a).. L. is shown as the seriessection and L, as the shunt section of the composite coil.The scanning coils are shown as Ly with the appropriatetransformer connexions numbered to correspond withFig. 1(a).

An equivalent circuit is shown in Fig. 3(b) where theshunt inductance is transformed across the scanning coilterminals 1-3. Thus the total inductance between theseterminals is given as:

reLp(L. + Ls)- (5)n2L5 + L. Ly

Now L1_, is required to remain constant with suitablechanges of inductances Lp, L., as previously described. Tosimplify design of the line scanning circuit it is convenientto make L, equal to the scanning coil inductance Ly. Thenthe inclusion of the width coils into the scanning coil circuitwill have little effect on the overall performance.

Hence making L,.. = Ly in equation (5) gives:L5 = Ly/n2 (Ly 1 '7)2 .11 L. (6)

Now with the coils adjusted for maximum picture width,(Le a minimum and Lp a maximum) some fixed fraction ofthe scanning current will be absorbed by the system and


before these values can be inserted into equation (6) it isnecessary to decide how much attenuation is allowable in agiven circuit.

An approximate calculation of this initial scan loss canbe made from Fig. 3(b) which assumes an infinite Q for allcoils involved. The assumption is also made that the scanwidth is proportional to the amplitude of sawtooth currentthrough L. This is, however, permissible for the smallchanges of scan we are dealing with.

The percentage of the maximum scan possible to thatobtainable in the " maximum width " position is given by:

actual scan n2 LD . 100100 = i,/i, .100 -maximum scan Lp' + L8 Ly

100per cent= 1 + (L.' Ly I n' L11)

(7)where L,' = Maximum value of shunt inductance.

L,' = Minimum value of series inductance.and all inductance values in millihenries.

6

5

0 0.25 05 op 75 I0 I25OUT CORE MOVEMENT k Inches) IN

Fig. 4. Variation of inductance with core movement for a long solenoid

The position has now been reached where the design ofa practical system can be commenced. An inductance figurefor the line scanning coils which is rapidly becoming astandard for domestic television receivers is 10mH. Takingthis figure for Ly and assuming a ratio of 10:1 for n, aninitial figure for Ls' can be chosen, say 0.4mH, which maybe substituted in equation (6) to give:

Lp = 0.1 + (1 /0.4) = 2.6mHand from (7):

percentage of maximum scan _ 1041

+ 10.4/260- 96 per cent,

i.e.: 4 per cent scan reduction.Taking this figure, for the moment, as an acceptable one,

these limit figures for Ls' and Lp will be used to derive theminimum scan condition. Using a ferrite core an induct-ance change of around 8 should be obtainable, givingfigures of 3.2mH for L, (max) and 0.33mH for Lp (min),the greatest scan reduction of :

100percentage of maximum scan _

1 + 13.2/33= 100/1.4 = 7F5

i.e.: a total inductance change of 96 -- 71.5 = 24.5 per cent.This means that if the line scanning circuit is designed to

give full scan plus 16 per cent then the width system shouldgive a control ± 12 per cent over the nominal picture width.

Determination of the Series and Shunt Core Movement-Inductance LawsUp to now only the extreme positions of the width con-

trol have been considered. in order to ensure that K ofequation (3) remains constant over the entire range of thecontrol it is necessary to investigate a little more closelythe manner in which Ls and Lp vary as the position of thecore is altered.

A typical curve showing inductance variation againstmovement of the ferrite core is given in Fig. 4. It will beseen that over the major portion of core movement theinductance change will be a linear one.

If we take this curve to show the manner of inductance

Ji

I2

OO

DISTANCE2 3 4OF CORE (Arbitrary Units)

5

Fig. 5. Required inductance variation for Lp to maintain L,..3 a constant

Fig. 6. Suggested tapered winding for Lp to obtain correct shunt law

variation for L, and substitute these values in equation (6)a graph is obtained showing the required variation for LI,during the same core movement (Fig. 5) and this is the lawof inductance change needed if K is to remain constantover the full range of the control.

Obtaining Correct Shunt LawOne method of obtaining this relationship is to use a

tapered winding for L (Fig. 6). The amount of taperingrequired is determined by experiment to give the closestapproach to the theoretical desideratum. Fairly closeapproximation can be obtained as is shown by the curvesof Fig. 7, but the coil is not easy to wind and is certainlynot suitable for factory mass -production in this form.

A simpler method is to adjust the spacing d (Fig. 2)between coil centres so as to use the shunt coil over thecurved section of its characteristic. This also is best doneempirically, and a series of curves is shown in Fig. 8 for


2

IE

Required Characteristic

Measured Characteristic

O 2L, (m H)

Fig. 7. Use of tapered shunt coil

Calculated minimum scan reduction :100= 100 - - 3 per cent

1 + 10.36/348Actual minimum scan reduction = 3.85 per cent.Calculated maximum scan reduction :

100= 100 -1 + 12.84/4

- 22 per cent-

Actual maximum scan reduction = 27.5 per cent.The actual scan variation being:

+ 13.6 per cent - 10.0 per cent.While the total E,H.T. variation measured = 5.5 per cent.

It will be seen from these results that some E.H.T. varia-tion does, in fact, occur, as the scan width is adjusted.

Fig. 9. Equivalentcircuit for differen-tial width circuitincluding coil re-

sistances

Fig. 10. Compari-son between a con -

3 tinuously variableinductance and aswitched tapped coil

various coil spacings. In this particular example a spacingof 1.4in would appear to give the closest approach to thedesired law.

Performance of a Differential Width SystemA pair of coils were designed in accordance with the pro-

cedure given above and with the distance between coilcentres adjusted to optimum the following figures wereobtained :

Ls (min) = 0.36mH Ls (max). = 2.84mHLi, (max) = 3.48mH Li) (min) = 0.46mHLy = 10mH n = 10d = 1.3in Ferrite core = 1.25in long.

xE

3-

2 -

Fig. 8. Effect of varying coil spacing

Spacing d=13in

Required Characteristic

Spacing c/=4.5 in

OL, (MH)

NOVEMBER 1954

2 3

eis

f3'

Q

Continuously Variable Inductance

Tapped Coil

INO

2

5 SWITCHPOSIT ION

CORE3 MOVEMENT (cm)

OUT

Although the amount of variation is quite small, it isinteresting to see why a variation should now occur.

Effect of Width Coil ResistanceOne factor that has, so far, been omitted from the

preceding calculations has been the Q -factor of the coils.This will, of course, vary as the coil inductance is alteredand as is seen from equation (1) will have an effect on theoverall Q factor of the scanning coil resonant circuit.

The complete circuit then, is as shown in Fig. 9, and ifvalues are given to Ly, Ry, n, and the coil resistances /2 andRs, an approximate expression for the overall Q of the com-plete circuit can be shown to be*:

250 + 80Q,, + 270Q,2 + 160Q,Qr - 400 + 60Qp2 (8)

For the case when :0,Ly 10mH Ry = 16

frequency = 1 000c/s R = 412 = Rp = Rsand Qs = Q of series coil

Qp = Q of shunt coil.Taking an extreme case of variation in Q factor for the

See Appendix A.


two coils from 1.0 to 10.0 then substitution in equation (8)will yield overall Q factors of 1.65 to 4.35. From equation(1) the E.H.T. variation will be found to be of the order of23 per cent all other factors remaining constant.

Consequently if the Q factor of the width coils could bemade constant over the range of control required, then atruly constant E.H.T. with change of picture width may beobtained.

Constant Q CoilsNo simple way of obtaining a continuously variable

inductance of this type, having a constant Q factor seemspossible: but an alternative lies in the use of a tapped coil.

This may be wound with different gauges of wire so that

Fig. 11. Damping cir-cuit across Ls

Fig. 12. Alternativeposition for Ls

the resistance increases from tap to tap in a manner pro-portional to the inductance change. Curves for a coil ofthis nature are shown in Fig. 10 for comparison with a con-tinuously variable inductance of the type previouslydiscussed.

Using two such coils in the series and shunt positions,a differential width system was constructed using a double -pole 5 -way switch to adjust the picture width.

This arrangement gave a scan variation of +11 per centfor a total E.H.T. variation of less than 3 per cent. This isprobably the best performance that can be obtained withsuch an ideal system, although the improvement over thecontinuously variable system hardly merits the additionalcomplication of coil taps and switching.

"Ringing" of Series CoilNo treatment of inductive width systems would be com-

plete without mention of the phenomenon of ringing orvelocity modulation of the scanning waveform due to thepresence of a coil in series with the scanning coils.

Any practical series width coil used will possess a certainamount of self -capacitance, which, together with the induct-ance, forms a tuned circuit with a resonant frequency inthe order of 200 to 600kc/s. When this circuit is sub-jected to rapid changes of current during the retrace period,it resonates and an exponentially decaying sinusoidal wave-form is developed across it. The duration of this oscillationpersists during the scan period and results in a modulationof the steady potential across the scanning coils.

The resulting velocity modulation of the scan is shownon the screen as a series of light and dark vertical linesextending from the extreme left-hand side of the screen

towards the centre, with diminishing intensity. The sameeffect may be present due to the scanning coils and may beobviated by tuning one-half of the coils'. In this lattercase, however, the frequency is rather lower and the twosets of ringing can be readily distinguished.

To reduce this shock excitation of the series coil, a damp-ing resistor may be connected across the coil. This increasesthe decrement of the tuned circuit and the oscillations areprevented from extending into the scan period. The exactvalue for this resistor is dependent on the coil used and isdetermined by experiment.

The value of resistance required to sufficiently reducethe amplitude of ringing will usually be such that an appre-ciable amount of energy is dissipated within the resistor.This has the effect of reducing the overall Q of the scanningcoil circuit and consequently the E.H.T. generated.

A better arrangement is to shunt L. by a series combina-tion of R and C as is shown in Fig. 11. It can be shown*that if the relationship :

L. = C R,2 (9)is maintained then the circuit may be made non -resonantand " ringing " will not occur.

In practice as L. is made variable, a new value of R, isrequired for each setting of the width control. A variablecontrol for R, could be fitted, but as the amplitude ofringing is inversely proportional to frequency it is sufficientto adjust R, with L. at the maximum value of inductance(minimum scan position.)

Although the width circuit of Fig. 11 has now beenrendered non -resonant it will behave as a capacitance atfrequencies of the order of 500kc/s. This capacitance inseries with the leakage reactance of the line scanning trans-former can form a tuned circuit having this order ofresonant frequency. Consequently ringing of this seriestuned circuit may be possible and produce unwantedvelocity modulation.

A solution to this problem lies in placing the seriessection of the width coil, together with the damping circuit,between the two line scanning coils as is shown in Fig. 12.The transformer leakage inductance is now no longerdirectly associated with L, and this source of ringingobviated.

APPENDIX A

To derive an expression for the overall Q of the circuitof Fig. 9 given certain practical values, viz:

Ly = 10mH R, = 15t2frequency = 1 000c/s n = 10and let R = R. = R,

Now the impedance of the circuit, looking from the trans-former is:

n2 (R, + jwlp) (Ry + R. + jwls + jwly)Z - (i)n'Rp nzjwLp + Ry + Rs + jwL. + jwLy

Expanding this and substituting Q,R, for coLp and Q.R.for (0L6 together with values given above:

Z - (15R - 62.8Q,R-QsQpRz) + j(QpR15 +62.8R + Q.122)(R + 0.15) + j(QpR + QaR/100 + 0.628)

(ii)

Neglecting term Qa/2/100 as very small, this expressionmay be rationalized to give :Z =(15R2 + 42R + 15Qp2R +063QsR +015QsQ,212)

+ j((63R + Q642 + Q8/22(1 + Qp2) + R(0.15QpR2+ 63Q,2))(iii)

Now substituting a figure of, say, 4S2 for R-a practicalvalue that can be achieved, a Q factor is obtained for this

* See Appendix B.


impedance of:250 + Qp42+ Q.16 + Q216 + 0.6Q5+40Q0+ 252Qp2

Q =408 + 60Qp2 + 2-5Q. + 0.6Q8Qp2

which reduces to:

Q - 250 + 80Q, + 27042,2 + 16Q5

400 + 60Q,2 (8)

APPENDIX B

Taking the circuit of Fig. 11 and including a resistanceR2 in series with L. to represent its distributed resistancethen the admittance of this circuit is given by:

which gives by rearrangement :

0,2 = 11 LsCL,

(iv)Ls-CR,'Now R2 will usually be very small and for practical

values of L. and C, CR.," can be neglected as very smallcompared with Ls.

Thus equation (iv) simplifies to :

0)2 = 1 1 LsC .-CR1 121 Ls}

(v)

and if :1 11/Z (I)

L. = CR,' (9)

then 0,2 is equal to infinity, i.e.: the circuit will be non -resonant.

REFERENCES

I. FRIEND, A. W. Television Deflection Circuits. RCA Rev. 8, 98 (1947).

-rationalizing

11Z -

+R2 + jtoLs R, + 1 / jo,C

each term:R, R

R,_ 0 ++ 1 ho2c2 R22 + w2L82)

2. SCHADE, 0. H. Magnetic Deflection Circuits for Cathode-ray Tubes. RCA

+ iiwLs

(ii)1 Rev. 8, 506 (1947).

3. SCHADE, 0. H. Characteristics of High Efficiency Deflection and High -voltageSupply Systems for Kinescopes. RCA Rev. 11, 5 (1950).

2110)CR, + 1 /(02C2 R.,2 ± (02Ls2at resonance the j terms are equal to zero, i e.: 4. JONES, E. Scanning and E.H.T. Circuits for Wide-angle Picture Tubes. J.

Brit. Instn. Radio Engrs. 12, 25 (1952).1 /idC (0/4,

(iii)5. SNOEK, J. L. Non-metallic Magnetic Materials for High Frequencies. Phillips

Tech. Rev. 8, 359 (1946).2 1 w2C2 - R22 + w2L.26. COCKING, W. T. Simple Line Scan Circuit. Wireless World, 43, 308 (1952).

Industrial RadiographyTwo new types of high voltage X-ray generator units have

recently been designed by the High Voltage Engineering Cor-poration of Cambridge, Massachusetts. They are for the radio-graphic examination of heavy castings and forgings and ofwelded structures.

The first is the Model JR one million volt generator and isdesigned for continuous operation at its rated output. Theexposure time is less than one minute for a thickness of steel oflZin rising to 30 minutes for thicknesses of 41in.

The voltage generator unit is mounted in a steel cylinder36in diameter and 50in length and consists of a Van de Graaffgenerator with its associated power supplies, belt driven motorand charging unit. The whole unit is pressurized up to2001b/in2 with nitrogen and carbon dioxide in equal amounts.

The multiple sectioned X-ray tube is of new design and can bekept in operation by an automatic titanium adsorber mountedin the base of the generator.

The principal characteristics of the Model JR are asfollows:-

Voltage-1 million, constant potential.Target current -0.01 to 0-25mA.Radiation output -8 Roentgens per minute at 100cm in

forward direction.Focal spot size-lmm.Half -value layer-0.6in steel.Field coverage -50° in forward directed cone with intensity

variation of less than 10 per cent.The unit can be suspended with a two hook sling and to providegreater flexibility in operation and transport a fork lift truckcan be used.

For permanent installations the unit can be suspended froman overhead gantry which permits a lifting range of 16ft, tiltfrom vertical to horizontal and a full 360° rotation.

The larger unit is the model AR two million volt generatorand is capable of radiographic examination of steel up to 10inwith an exposure time of less than one minute for steel notexceeding 5in thick.

The voltage generator is a Van de Graaff generator in a steelcylinder in which is also mounted the multi -sectioned X-raytube. The vacuum pumping system for the X-ray tube consistsof a high speed mercury diffusion pump, cold trap, mechanicalpre -vacuum pump, vacuum gauge and protective circuits. The

whole unit is mounted at the generator base on a swivel jointso that the unit remains vertical irrespective of the generatorposition.

A desk type console contains the necessary operating controlsand monitoring facilities for generator voltage, target current,focusing current exposure time. The principal characteristicsof the Model AR are:

Voltage-Two millions electronically stabilized.Target current -0.01 to 025mA.Radiation output -75 Roentgens per minute at 100cm

measured in forward direction.Focal spot size-imm.Half value layer-0.83in steel

The generator is supported on two trunnions which are attachedto a yoke containing the motor drives for tilting the unit androtating the yoke assembly. Where a high lift is required adouble set of telescopic box members are provided to which theyoke can be attached assuring a rigid sway -free mounting.

The model AR two million volt generator in use at the Foster WheelerCorporation.

NOVEMBER 1954G


An Even -Harmonic Magnetic Amplifierand Some Applications to Measurement and Control

By P. D. Atkinsont, M.A., A.M.I.E.E., and A. V. Hemingway*, B.Sc., A.M.I.E.E.

The even -harmonic magnetic amplifier described has a zero stability of better than 10-" wattsinput power and in this respect represents a significant improvement on conventional magneticamplifiers. Its application to multi -stage magnetic amplifiers for the automatic control of street

lighting and the measurement and control of temperature are described.

MAGNETIC amplifiers are used in increasing numbersin industry to amplify the electrical output of sensitive

detecting elements (e.g. photocells, resistance strain gauges,thermocouples) and to operate relays or indicating orrecording instruments'. The power level of the electricalsignal from such detectors is often so low that zero driftin the magnetic amplifier sets a limit to the accuracy whichcan be achieved.

Using conventional balanced magnetic amplifier circuitsthe zero error over long periods can generally be madeless than the zero shift produced by an input power of10-I to 10-9 watts. Normal variations in supply voltageand frequency, and drift in rectifier characteristics makeit difficult to improve on this. However, even -harmonicmagnetic modulators' used with electronic amplifiers areknown to have considerably better zero stability; figuresfor zero drift ranging from 10' to 10-" watts input

are quoted depending on the mode of operationof the modulator and on the design of the electronicamplifier and oscillators". The amplifier to be describedin this article has been developed to meet a need for asimple robust device with a zero stability appreciablybetter than can be achieved using conventional magneticamplifier techniques'. A long term zero stability of betterthan 10-" watts input power can be obtained with nomore care than is required to achieve a figure of 10-' wattsusing conventional methods.

The use of even -harmonic magnetic amplifiers has madepossible reliable static apparatus for a number of applica-tions which are outside the range of conventional tech-niques. Two such applications are discussed in some detailin the latter part of this article.

The Basic CircuitThe even -harmonic amplifier is an adaption of the

even -harmonic modulator which is used as a D.C. to A.C.convertor for an electronic amplifier'. The design andmode of operation, however, are such that it will givea useful power output. Typical performance figures are :power gain 1 000, power output 1 mW. It will operatesatisfactorily over a fairly wide range of supply voltageand frequency and is suitable for connexion to the 50c/smains supply; a stabilized supply or an electronic oscillatoris not required.

DESCRIPTION OF CIRCUITThe circuit is shown in Fig. 1. Windings a and a' carry

an alternating excitation current supplied from a mainstransformer through a limiting resistor R. Windings band b' carry the input or control current; they are con-nected in series opposition with respect to the excitation

Elliott Brothers (London), Limited.t Now at British Tabulating Machine Co., Ltd.

windings so that if the cores and windings are identicalno voltage at the supply frequency can appear at the inputterminals. The output windings c and c' are connected "inthe same way as the control windings. One pair of wind-ings could be used for both purposes, but it is usuallyconvenient to isolate the input and output circuits.

When the control current is zero no voltage can appearat the output terminals xx'. If a direct current flows inthe control windings a voltage containing only even -harmonics of the supply frequency will appear at xx'. Thechoke L is included in the input circuit to prevent the

ControlCurrent

InputTuning/ I

Capacitor

Fig. 1. Even -harmonic magnetic amplifier

Output Current

control circuit from presenting an inductively coupledshort-circuit across the output terminals. The alternatingoutput voltage is rectified and smoothed to give a directcurrent output. Thus a direct current flowing in the controlcircuit causes a direct current to flow in the load circuit.

CHARACTERISTICSAn arrangement of this type may be expected to have

a good inherent zero stability. For, with a balanced pairof cores, the output is zero if the input is zero and thiscondition is independent of the voltage and frequency ofthe excitation. The sensitivity, or current amplification is,in general, dependent on supply voltage (Fig. 2(a)). How-ever, over a fairly wide range the sensitivity is almostindependent of supply voltage and frequency and therelationship between control current and output currentis approximately linear.

The excitation voltage in the working range is of theorder of three times that required to produce saturation.The cores are therefore both saturated for the greater part


of each half cycle of the supply voltage and the voltageat xx'. consists of short pulses generated at each reversalof the excitation current (Fig. 3). The polarity of thesepulses is determined by the polarity of the control current.Within the working range an increase in supply voltageproduces both an increase in amplitude and a decrease inlength of the output pulses. Thus the charge transferredto the smoothing capacitor by each pulse is nearlyindependent of the supply voltage. (A detailed analysisof this mechanism is given in Ref. 6.)

Both input and output impedances may be arranged tohave any value up to about 3k1.1.

TUNING OF THE CONTROL WINDINGAn increase of about 2 : 1 in the current sensitivity of

the amplifier can be obtained by tuning the output wind -

1600

1200

crttU0 8000-J

r"Working-- Range --7

V.--

---.....5.2...

../

WorkingRange

-<(----

/

1 140 180 220R.M. S. SUPPLY VOLTAGE (Volts)

Fig. 2. Typical regulation curves for even -harmonic magnetic amplifier.Control current 50 µA.

(a) With tuning(b) Without tuning

ings. This is usually done by connecting a capacitor acrossthe control windings as indicated in Fig. 1. The naturalperiod of the tuned circuit formed by the winding induc-tance and the capacitor should be somewhat less thanthe total length of the output pulse, T in Fig. 3(b). Inaddition to increasing the current sensitivity, the tuningcapacitor causes a damped oscillation in the output circuit(Fig. 3(c)) and modifies the regulation curve (Fig. 2(b)).CONSTRUCTION

The considerations governing the assembly of the mag-netic circuits and the arrangement of the windings are thesame as in the case of ordinary magnetic amplifiers.Identical construction and winding techniques are used andthe only physical difference between an even -harmonic anda conventional magnetic amplifier is in the details of thewinding design and in the circuit connexions.

The even -harmonic amplifiers used in the applicationsto be described contain 0.005in thick Mumetal laminationsof outside dimensions lgin x I lin. An assembly com-prising the two cores and the associated windings occupiesa volume of approximately liin x 1 iin x 1 lin.

Balanced CircuitsThe circuit described above, while representing a

valuable improvement on the conventional magneticamplifier in respect of stability, has two practical dis-advantages.

(a) The polarity of the output does not reverse with thepolarity of the input.

(b) Since the rectifier has a very high forward resistancefor applied voltages less than about 400mV thesensitivity of the amplifier at and near to zero outputis very much less than normal. (Because therectifier passes current in short pulses this effect isapparent only for very low values of mean outputcurrent.)

(a)

(b)

(c)

(d)

441

N.,

Fig. 3. Output voltage waveforms

X

Fig. 4. Balanced output circuits(a) Joined load circuits(b) Single load circuit

SupplyVoltage

Pulse, at.xx

Pulses atxx c antral

windingtuned

Pulses atxx' unbabn-ced cores

Load

These difficulties may be overcome by unbalancing thetwo cores, usually by connecting a suitable resistor inparallel with one of the excitation windings. The voltageat xx' when the control current is zero then containsfundamental and odd harmonic frequencies, and consistsof alternate positive and negative pulses as shown inFig. 3(d). The effect of positive control current is toincrease the amplitude of the positive pulses and reducethe amplitude of the negative pulses, and vice versa fornegative control current.

Two output circuits used with the unbalanced corearrangement are shown in Fig. 4. The one in Fig. 4(a)has two pairs of direct current output terminals; when


the control current is zero equal currents flow in the twoload circuits and the rectifiers are operated above thebottom bend in their characteristic. The amplitude andsign of the difference between the two output currentsis dependent on the control current; the characteristic islinear and symmetrical about the origin. The doubleoutput circuit restricts the use of this circuit to applicationswhere the two currents can be subtracted convenientlyand it is frequently used as a pre -amplifier for a con-ventional magnetic amplifier. The stability of gain iscomparable with that of the single output circuit whilethe zero stability is appreciably better.

The output circuit shown in Fig. 4(b) has similarcharacteristics to that in Fig. 4(a) and the single outputcircuit is an advantage in some applications. Because theonly comparison elements are the two rectifiers insteadof the complete output circuits the zero stability, expressedas an input power is improved in the ratio of approxi-

similar applications the controller can be set to operateat any time during the period of some 40 minutes aftersunset and some 30 minutes before sunrise. The minimumoverall range of light intensity over which the control mustoperate is estimated to be between 1 and 71 foot-candles.Daylight intensity on a bright day often exceeds 1 000 foot-candles; this must not damage the light sensitive elementnor cause damage to or faulty operation of the controller.

THE LIGHT SENSITIVE ELEMENTA selenium barrier -layer photocell (67mm diameter) is

used as the light sensitive element. It is mounted in asealed housing and in order to avoid undue ageing dueto prolonged exposure to direct sunlight only diffused day-light is permitted to fall on it. An important advantageof this type of cell is that it has an internal impedanceof a few thousand ohms and thus the lead from photocellto amplifier can be of any reasonable length.

In order to provide the required accuracy and range of

Fig. 5. Amplifier for automatic lighting controller

mately 5 : 1. The power gain is reduced by about 2 : 1.The rectifying action depends on the bottom bend of therectifier characteristics and the allowable degree of coreunbalance involves rather more careful setting up thanis necessary with the other balanced output circuit. A dis-advantage of this output circuit is that it is readily upsetby voltages fed back from the next stage in a cascadearrangement. It is therefore not suitable for use as a pre-amplifier for a conventional magnetic amplifier but it canbe used to feed another even -harmonic amplifier.

The combined characteristic of the two rectifiers inFig. 4(b) is a symmetrical one and they can be replacedby a single silicon -carbide resistor thus eliminating possiblezero drift due to differences in rectifier characteristics.The use of a silicon -carbide resistor leads to lower sensi-tivity, however, and, since the selenium rectifiers givesatisfactory performance in respect of the zero stability,they are normally preferred.

Automatic Street Lighting ControllerAn automatic lighting controller provides an example

of the use of even -harmonic magnetic amplifiers in anon -off control system. The controller is designed to switchon lighting circuits automatically when the daylightintensity falls below a pre-set value and to switch themoff when it rises above this figure. It can therefore beemployed where the control of street lighting, publicillumination, traffic direction lights at roundabouts, etc.,is required at a given light intensity.

REQUIREMENTSFor public street lighting the normal "switching -in" time

is approximately 20 minutes after sunset; similarly, thenormal switching -out time is approximately 15 minutesbefore sunrise. In order to make it suitable for other

Adjustablebias for

setting control

Fig. 6. Automatic lighting controller show;ng magnetic amplifier and relayin a weatherproof case, and photocell housing

operating intensity the amplifier, whose input impedanceis about 2 00011, is designed to give reliable operation ofthe relay for a change of input current of 0.5,uA at anypre-set value between 0.5 and 20µA.

THE AMPLIFIERThe amplifier, Figs. 5 and 6, consists of three stages in

cascade. The output stage, which is a parallel -connectedmagnetic amplifier of conventional design, controls a relay(P.O. 3000 type carrying a mercury switch) capable ofswitching a load of 10A at 250V. The first two stages areeven -harmonic magnetic amplifiers of the type described.The input current required to operate the relay is set byadjusting the bias current on the output stage.


Laboratory tests on the effects of variations in supplyvoltage and ambient temperature showed that the zerostability of the controller for normal settings correspondedto an input power of about 10-" watts or a light intensityof 0-07 foot-candles. Field tests carried out over periodsof many months showed no measurable drift due to ageingof components, etc.

An Amplifier for Thermocouple E.M.F.sThis amplifier was developed as a reliable and robust

instrument amplifier particularly for use with thermo-couples. The normal sensitivity gives full scale output forapproximately 42mV (corresponding to 100°C temperaturedifference with a copper-constantan thermocouple). Theoutput, 5mA into 50012, is sufficient to operate a largeindicating instrument and/or a direct writing recorder.A simple modification of the amplifier makes it suitablefor use in an on -off temperature control system.

NEGATIVE FEEDBACKTo achieve the accuracy and stability required for an

instrument amplifier it was necessary to provide negativefeedback over the complete amplifier. Magnetic amplifiers

10

3- 50

t- 0u.

c2 50

10

r-----.*- --*4-3r-..-- -_-_,

Tu.- : _- .1,-_ L_____.1-_-

0 I 2 3 4 5 6 7

TIME FROM SWITCHING ON ( hours)

Fig. 7. Initial drift of instrument amplifier

are usually considered to be so stable that the sacrificein gain associated with negative feedback is unnecessary.The reasons for using negative feedback in this case areas follows :

(a) A feedback voltage proportional to the output currentis injected in the input circuit in opposition to thethermocouple E.M.F. The current flowing in the inputcircuit is therefore small and the resistive drop inthe circuit is small compared with the input and feed-back voltages. Thus variations in the resistance ofthe copper winding and the thermocouple leads haveonly second order effects.

(b) In a multi -stage amplifier, particularly when even -harmonic amplifiers are used, it is not practicableto maintain a linear characteristic which is stablewith normal variations in ambient temperature andsupply voltage and frequency.

THE AMPLIFIERThe amplifier comprises three stages in cascade. The

first two are even -harmonic amplifiers and the last is aconventional balanced magnetic amplifier. The core andwinding assembly of the first stage is enclosed in a Mumetalcan to shield it from the earth's magnetic field. A pro-portion of the output current flows through a small resistorin the input circuit to provide the overall negative feed-back. In order to avoid spurious thermo-electric E.M.F.sin the input circuit the feedback resistor is wound withmanganin wire and junctions between dissimilar metals areavoided.

The output stage was designed to have as slow a responseas practicable. This was necessary in order to stabilizethe closed feedback loop by making the lag in one of thethree stages very much greater than that in either of theother two. Some form of internal gain control wasnecessary so that the loop gain could be set to its bestvalue. The method which was chosen as having the smallest

effect on zero setting and zero stability was that of anadditional negative feedback loop enclosing the two even-harmonic amplifiers. The loop gain here is small but itprovides the necessary degree of control over the gainround the main loop.

Fine controls of zero setting and of overall gain areprovided. The gain control is an adjustment of the pro-portion of current feedback and the zero setting is avariable bias on the first stage.

Test results obtained using a matched input of 1011resistance show that the characteristic, which is symmetri-cal about the origin, is linear within -±1 per cent full scaleoutput. With combined variation of supply voltage, ± 10per cent, and frequency, ±5 per cent, the zero error wasless than 8/AA (10-12 watts input power or 0.16°C with acopper-constantan couple) and the maximum error in the5mA output was 20µA (6.4 x 10'2 watts input power or0-4°C). (See Fig. 7.)

Long term drift tests showed no significant zero driftor change in sensitivity.

The response time of the amplifier to a sudden changein input is about 21sec.

THE CONTROLLERThe amplifier without its negative feedback circuit is a

high gain amplifier with good zero stability suitable foruse in control systems. When used for furnace temperaturecontrol the output circuits of the two magnetic amplifierswhich comprise the output stage are separated and eachcontrols an independent relay. The bias currents suppliedto each of the output stages are independently adjustableso that the two relays which control separate sections ofthe furnace heater can be arranged to operate at slightlydifferent temperatures, a feature commonly provided inthe "chopper -bar" type of controller.

The main backing -off bias which determines the tem-perature at which the relays operate is provided by passinga current through a small resistor in the input circuit.When, as is often the case, the controlled temperatureexceeds 300 to 400°C the main cause of error in the con-troller is the backing -off current which is normally obtainedfrom a neon stabilized supply. Switching errors of theorder of 1 or 2°C can be expected from this source com-pared with / to 1°C due to the amplifier.

ConclusionThe even -harmonic magnetic amplifier is a useful

addition to existing magnetic amplifier techniques; itreduces the gap between the zero stability obtainable withthe magnetic modulator type of electronic amplifier andthat obtainable with solely magnetic techniques. The usefulrange of input impedance, up to about 3k1l, makes it suit-able for use with many types of transducer but its poorresponse time restricts its application to cases where theinput is a slowly varying quantity.Acknowledgments

The authors are indebted to Messrs Elliott Brothers(London) Limited for permission to publish the informa-tion contained in this article, to their colleagues,Messrs J. H. Aird and J. A. Chitty, for their assistance andsuggestions in the work described, and to the Institutionof Electrical Engineers for permission to reproduce Fig. 7.

REFERENCESI. GALE, H. M. Magnetic Amnlifiers and their Application to Industrial

Purposes. Trans. Instrum. Meas. Conf. Stockholm (1949).2. PIZZEY, C. F. British Patent No. 62987 (1946).3. BREWER, A. W., SQUIRES, J., Ross, H. McG. Some Developments in Electronic

Magnetometers. Elliott J. I, No. 2, 38 (1951).4. NOBLE, S. W., BAXANDALL, P. J. The Design of a Practical D.C. Amplifier

based on the Second -Harmonic Type of Magnetic Modulator. Proc. Instn.Elect. Engrs. 99, Pt. 2, 314 (1952).

5. HEMINGWAY, A. V., ATKINSON, P. D. British Patent Application No. 113/49.6. FROST -SMITH, E. H. The Study of a Magnetic Inverter for Amplification of

Low -Input -Power D.C. Signals. Proc. Instn. Elect. Engrs. 100, Pt. 2, 362 (1953).

NOVEMBER 1954 485 ELECTRONIC ENGINEERING.

A Torquemeter for Testing Gas TurbineComponents

At 11 000rev/min 500kW(Part 1)

By J. F. Field* and D. H. Towns*

Since the useful power output of a gas turbine is the difference between two relatively largerquantities (i.e. compressor and turbine energy), it is important that the thermodynamic efficiencyof both compressors and turbines in any such engine should be most accurately determinable.The most satisfactory way of doing this involves accurate measurement of mechanical power outputor input; a variety of torquemeters have already been developed for the purpose; hitherto these

have not had a': accuracy of better than about 2 per cent.An improvement in accuracy to about per cent has been achieved by introducing a multiplefrequency phase -angle measuring device, which the authors have called an " Electronic Vernier".

OME three years ago the Electricity Supply ResearchCouncilt, when considering the application of

gas turbine technique, to steam power', thought itadvisable to determine experimentally whether it waspossible to compress steam in an axial flow compressor,as used in gas turbines,with about the same effi-ciency as when compress-ing air, and whether thesteam could be compressedalong a wet adiabatic withno deterioration in effi-ciency.

It was decided to setup a test rig for drysaturated steam at thecompressor inlet andto inject enough finelydivided water to enablethe compressor to workapproximately on thedesired wet adiabatic. Itwas hoped that if the waterwere in a fine enoughstate of suspension thecompressor efficiency would be as high as with drysaturated steam. The latter effect would inevitably indi-cate itself as a reduction of power input to the compressorwhen the water mist was injected. The fundamentalrequirement was a very accurate indication of change ofpower input with a change in dryness fraction of thesteam, since this would have the great advantage ofeliminating errors due to insufficient accuracy in weighingthe quantity of steam compressed under given conditions.It is in effect a null method of testing. Its success dependson attaining especially high sensitivity to small changesof power or torque at a fixed speed and it is the purposeof this article to indicate the manner in which this wasachieved.

A review was first made of known methods of powermeasurement at high speeds, the results of which may besummarized as follows : -

(1) A Continental installation was inspected, in whichthe compressor driving motor was arranged to swing about

* South East Scotland Division, British Electricity Authority.t At that time under the Chairmanship of Sir Harold Hartley, F.R.S., and now

under the Chairmanship of Sir David Brunt, Sec. R.S.

General view or calibration test rig for high speed torquemeter. Normallythe main motor drives the speed increasing gearbox through a Sinclairfluid coupling, the input speed being 3 000revl min. For calibrationpurposes, the fluid coupling has been removed and a low speed chaindriven jackshaft substituted, so that the torquemeter speed for calibration

is some 2 300rev I min.

a highly sensitive weighing machine mechanism so thatthe reaction torque on the motor under load conditionscould be measured. This machine was, however, expen-sive and the delivery time long.

(2) As an alternative to (1) above, the use of thecompressor itself as a reac-tion component was con-sidered but the idea wasnot pursued owing toprobable serious errorscaused by reaction fromthe inlet and outlet steamvelocities.

(3) There are one or twotorquemeters which useelectrical strain gauges butthese appear to be ofsuspect stability.

(4) One very goodtorquemeter was shown tothe authors under develop-ment, this dependingon a comparatively smalltorque member of highstability steel, the exceed-

ingly small angle of twist being measured by an opticalmultiplying device.

(5) A torquemeter similar to (4) above, developed forthe Royal Aircraft Establishment, and described by theNational Gas Turbine Establishment in one of their earliestpost-war papers, measured the angle of twist by means oftwo phonic wheels, one at each end of the torque member,the change of phase of the alternating voltage at one endwith respect to the other being measured by means of anelectronic phasemeter. This apparatus gave an accuracyof measurement of twist, and so of transmitted torque,of about 2 per cent and had been originally conceivedto function under airborne conditions on the short lengthof shaft between an aeroplane engine and the propeller.

This idea gives the prospect of almost unlimited accuracybecause a torsional shaft movement (however small) canbe stepped up to a readable figure by raising the frequencyof the nhonic wheels, i.e., increasing the number of elec-trical degrees relative to the actual twist in mechanicaldegrees, the limiting feature being the frequencycharacteristic of the phase -angle meter itself. Eventuallyit was considered that the phonic wheel was not as suitableas an arrangement of exciter lamps and photo multiplier


cells, the phonic wheel at each end of the torque memberbeing replaced by a stainless steel disk with 120 +-in dia-meter holes on a pitch circle diameter of 9.9/16in. Ata speed of 11 000rev/mM this gave an alternating voltagesignal of 22kc/s. and a small inherent frequency error inthe phase -angle meter, but at the same time gave enoughelectrical degrees for an exceedingly small twist in theshaft to show up quite clearly on the phase -angle meter.The obvious additional step to increase both the absoluteand differential sensitivity was to lengthen the torquemember and at the same time reduce its diameter to aslow a figure as kept the material reasonably within theelastic limit.

The relatively considerable length and twist should alsocompletely swamp any errors due to bearing clearancesbut the additional precaution was taken of calibrating thetorque meter against a Heenan & Froude dynamometer at2 300rev/min, a separate very small correction then beingapplied for frequency effect at 11 000rev/min. Thisfrequency error can be accurately determined by render-ing the torsion assembly axially solid and running itunloaded first at the speed of calibration and then atthe working speed. Errors are mainly due to harmonicvoltage effects in the photocell generators and can belargely eliminated by the precautions described later.

Heenan and Froude magnetic or hydraulic drag dynamo-meters are in effect weighing machines incorporating aslipping clutch. For a given maximum torque thoserequired to operate at a relatively high speed involve arelatively high dissipation of power. Accordingly theirconstruction is heavier and the weighing machine com-ponents are less accurate than those designed for slowspeed measurement. Hence there is an obvious advan-tage in choosing for calibrating purposes the lightestconstruction which can absorb the torque, necessarily ata relatively low speed.

A magnetic type dynamometer of light construction wastherefore selected as the basic standard. This has anaccuracy in the upper range of readings of better than

per cent. The further loss of accuracy inherent in theprocess of transfer to the torquemeter is probablyexceptionally small, i.e., less than 01 per cent.

The above method of calibration is considered not onlyat least as reliable as any method of static calibration, butbearing in mind that re -calibration should certainly becarried out before and after each test, is far easier toapply since mechanical details of static calibration wouldbe complicated and expensive compared with the extremesimplicity and freedom from errors in the dynamometersubstitution method.

A torsion rod of the kind proposed was bound tosuffer slightly from hysteresis and it was necessary tocompromise in the maximum shear stress allowable atthe surface of the material. It was decided that the mostpractical material would be the special torsion rod steeldeveloped in recent years for motor car springing wherehigh stability over a large number or strain cycles ofwidely varying amplitude is now obtained. Fortunately,a torsion rod made by the English Steel Corporation fora well-known motor car front end suspension was suitable.This torsion rod is some 4ft 3M long with heavy serrateddumb -bell ends to take the drive and with a diameter ofabout 0.935in; thus the effective part is roughly 50diameters long. The material is described as silico-manganese spring steel. For motor car use, these torsionrods are oil hardened and tempered in a controlledatmosphere. The material is then shot -peened and painted.The rods are invariably pre-set after heat treatment bytwisting one end with respect to the other by about 90',i.e., somewhat further than the full travel of the rod wheninstalled in the car. This gives a pre-set in the torsionrod of roughly 10°and thereafter it is very stable in normaluse. The material would appear to be ideally suitable

for a torque measuring device provided there is no diffi-culty due to hysteresis. It was found in practice thathysteresis gave no trouble in making very accurate measure-ments, provided the torque was always measured fromthe same side, e.g., under gradually increasing torqueconditions, and the calibration was remarkably consistentunder repeated variations of load. During the tests, themaximum load was about 350kW and the maximum strainwas equivalent to some 7° mechanical

The possibility of modes of lateral vibration and oftorsional oscillation due to the heavy mass of the com-pressor rotor under surging or pulsating steam flow con-ditions, resulting from the use of a long thin torsion rod atthis very high speed, were dealt with by enclosing the rodin a stiff concentric tubular shaft with continuous lightalloy support bearings, the rod resting on a thin film ofoil throughout its entire length. The shot -peened surfaceof the rod was lightly honed without removing the iden-tation which carried the oil film. Torsional vibrationwas eliminated by a vane oil damper between the twoconcentric outer shaft bodies. The layout of the torsionrod component as a whole is indicated in Fig. 1. Oil isinjected into the damper cylinder by means of an ordinarygrease gun at four equi-distant nipples and it is essential,because of the high centrifugal forces, to have effectivesealing plugs, each consisting of an Allen screw with aball -bearing to retain the oil after the damper chambershave been filled.

The strain of 6° to 7° mechanical is equivalent with120 equi-distant holes in each disk to some 700° to 800°electrical. The phasemeter cannot, however, show morethan 90° electrical on its scale, a reading of 90° to 180°being achieved by the return of the meter pointer tozero. Thus there is a complete cycle, minimum to maxi-mum reading and back again, for each 180° electrical.To keep track of the number of such complete cycles ofmovement a second signal 1/10th of the frequency isgenerated by each disk by means of the twelve rectangularnotches on the disk periphery and an associated photocell.By switching over to the low frequency signal (2.2kc/s) acoarse reading over a range of 70° to 80° electrical isobtainable and clearly establishes the precise quadrantof the high frequency high sensitivity reading. The ideais analagous to that of an hour hand to supplement theinformation given by the minute hand of a clock and hasbeen described by the authors as an electronic vernier.

An important application of this instrument is thepossibility of measuring with a high degree of accuracythe exchange of power in free running gas turbine com-pressor units such as are often utilized in compound gasturbine cycles, since a precise knowledge of the actualexchange of power is bound to be a considerable stepforward in interpreting the normal temperature andpressure measurements. In such an application the torque -meter would probably have to withstand a considerablethrust load necessitating the introduction of a ball or rollerthrust bearing in such a way that it would have no appre-ciable effect on the torsion rod calibration.

In ship propulsion, where advantage can be taken of theoften considerable length of the propeller shafts, it wouldbe advisable to attach the photocells to a tubular stationarycomponent mounted around the shaft and supported onit by means of suitable anti -friction bearings, the stationarycomponent being prevented from rotating by an armattached to the hull. The photocells would then be immunefrom errors or cyclic variations due to the working ofthe ship's hull and would be truly concentric with the shaft.

Calibration of the particular length of propellor shaftwould have to be carried out on shore either against awater brake or by means of a static test. The arrange-ment for such a static test would consist of mounting thephotocell assemblies on the shaft at the positions normallyoccupied by the disks and rotating round the shaft a


z0U)0

WS

a

W

docC

yLL ZyZ < >. tr,

,-> < W

8gig

ELECTRONIC ENGINEERING

Lt:

tubular member carrying two per-forated disks similar to thosenormally used on the shaft. The

rew >. Q stationary propellor shaft would bea.2

0 a 0 subject to torsion by a suitable0 CC

<m0

R m cantilever and weights, while at thesame time the outer tubular memberand the perforated disks would berotated at a speed corresponding tothat of the shaft when in the ship.

In the case of large electricgenerators, the power output ismeasurable by electrical meteringwith a high degree of precision and

tal 0.

I- Ldit is more useful in this case to

Y ai L:,' measure only the losses amountingN LL,

0 ,,.o to about 2 000kW in the case of a. .:(

ar 0a 100 000kW 3 000rev/min machine..6, w ,}- For this purpose a torsion rod of. cs. ?,' similar material to that already used,

1 about 24in diameter and say 10ft; long would suffice, the actual length

depending on the diameter of thewheels. Internal stops would berequired in the outer concentrict shaft and oil damping gear so that

X the acceleration of the heavy mass

A '1**,

, ini// _,a 1.

cooling water condition.," 4 WO

CI. U- ou. a Electronic ComponentsW x < 1

o..1a i z <ow ,.<I: The phase -angle measuring device< oO a ,:c was designed by the Royal Aircraft

o 5 Establishment and was developedo

1.-

z i and produced by McMichael RadioE Ltd. In its original airborne form

0w § it was operated from a 14 volt D.C.

ul 0 a>z I supply, had a frequency range ofaw<

.500c / s to 40kc / s, a maximum

i error of +2', and was known as0,0

% le,-1

a torquemeter, but the authors

k Iwere able to make use of a later

1 version of this instrument, which

it../

CC W.

C.1 a is intended for operation from A.C.aa., mains, has a frequency range of

1asI 'w 2< 20c/s to 50kc/s, a maximum error7 a of only +1°, and, since it is capable

1 1°31. <zz 2 of application to many kinds of

; &phase measurement apart fromthose appertaining to the determina-

I 13 6 "<z tion of torque is known as a phase -

meter. There are other forms of1 1

.:71 E c.S phase measuring gear which mighti

0, si

s

U. '- also be adaptable to this purpose.0z Z

Ow The basic circuit of the instru-4! r 1 0O

-,,,,, a-4 ment can be represented by two

rt41

. ri -2 ' (I '2.- 1:3'

0 0 <. 4 Z

Z I -

III - ammeter, and an electronic switchresistors of equal value, a milli -

having two positions, x and Y (Fig.

0

0 jAl 1/4

..1 wI- c w z

2). When the switch is in positiono I

.7, ,7,1 tx, current flows through the meterin one direction and when theswitch is in position y, an equalcurrent flows through the meter in

0 1of the electric rotor would not over -

w twist the torsion rod when startingzacc

gi, up. It would then be possible toW g § carry out short-circuit stator current)-

d .°3 2 tests and open -circuit excitationL. .a3 lil

,... tests and so obtain the losses aloneo z <

.?, under simulated full load operating9 g,-cc conditions and temperature, moreu wNet.

AIA 2

Paaccurately than has been possible

$ a i by conventional loss tests based on<

488 NOVEMBER 1954

the opposite direction. Fig. 3 shows a series of waveformsof two alternating voltages between which it is requiredto measure the phase displacement, and which comprisesthe inputs to the phasemeter. The operation of the phase -meter is such that when one of the two alternating voltagespasses through zero going from negative to positive, the

(0)

(b)

(c)

(e)

(a- ) (b)

Fig. 2. Basic circuit of phasemeter

2mA

0-2mA

2mA

0

-2mA

2mA

O

-2mA

2mA

0

-2mA

Fig. 3. Phasemeter input and output waveforms

switch moves to position x, and when the other alter-nating voltage passes through zero going from negativeto positive, the switch moves to position Y. These switchinginstants have been designated x and Y to correspond tothe switch positions and are shown in Fig. 3, togetherwith the waveform of the current in the meter. Except

at the very lowest frequencies the meter cannot respondto the positive and negative pulses of current, and indi-cates only the mean current during one cycle. The result-ing relationship between mean meter current and phasedisplacement is, therefore, of the form shown in Fig. 4,the current varying in rectilinear manner from 2mA positiveat 0° phase displacement to 2mA negative at 360° phasedisplacement, passing through zero at 180° phasedisplacement. Although the relationship between metercurrent and phase displacement theoretically exhibits adiscontinuity at 0° and 360° (which are identical points inangular measure), in practice the current will follow thedotted line in Fig. 4 for the following reasons. If there areN alterations of voltage for each revolution of thegenerator, there will be N switching instants x and Nswitching instants Y per revolution. At changeover fromphase displacements less than 360°, when Y precedes x,to phase displacements greater than 0°, when x precedes Y,it is not possible for mechanical reasons to ensure that all

2mA

90o 180 270°PHASE DISPLACEMENT

360°

-90° -45° 0° 45° 90°METER SCALE READING (Shunted)

L A9000ò 90°

METER SCALE READING (Unshuntsd)

XY XY

I

Fig. 4. Characteristic of phasemeter

XY Vs XY XY ÌX Vs XY YX YX YX

Fig. 5. Current in phasemeter output circuit dur ng changeover period

N switching instants in one revolution of the generatorsimultaneously change over from Y preceding x to x pre-ceding Y. It is, in fact, reasonable to assume that theychange over one at a time in a random sequence, so thatthe changeover is spread over a band of phase displacementvalues, the width of the band depending on the accuracywith which the generators are constructed and extendingin a typical case from say 0° to 20° and 340° to 360°.

During the changeover period, the meter current hasneither the waveform shown in Fig. 3(a) nor yet that shownin Fig. 3(e), but is instead a combination of the two asshown in Fig. 5.

The meter movement has a full scale deflexion of lmA,has its zero at one end of the scale, and is provided witha reversing switch. Zero on the meter scale is marked 0°and full scale deflexion is marked 90°. Thus the meterindicates 0° when the inputs have a phase displacement of180°, it indicates 90° when the inputs have a displacementof 270°, and it indicates -90°, i.e. +90° with the reversingswitch in the other position, when the inputs have a dis-placement of 90° (Fig. 4). The advantage of this arrange-ment is that for a total change of phase displacement notexceeding 180°, the available scale length is utilized to themaximum extent.

Where it is required to measure phase displacements inexcess of 180°, the meter can be shunted by means of


Fig. 6. Phasemeter output stage

11.7

switch S (Fig. 8) and its sensitivity halved. While it isthen theoretically possible to measure phase displacementsup to 360°, in practice this may be limited to say 320°,since, as already explained, that part of the phasemeterrange in the neighbourhood of 0° and 360° is unusableowing to the inherent inaccuracies which are bound to bepresent in the construction of any voltage generator, andto the inability of the phasemeter itself to resolve verysmall phase displacements.

The electronic switch, which has a useful frequencyrange from 20c/s to 50kc/s, comprises two pentode valvesconnected to form a D.c.-coupled trigger pair, as shown inFig. 6. This circuit has two stable states, in one of whichthe current flows through the meter in one direction, andin the other of which an equal current flows in the oppositedirection. The circuit is triggered into one or other of thetwo states by means of pulses applied to the control gridsof the valves, the pulses being derived from the two volt-ages between which it is required to measure the phasedisplacement. In order that the meter indication shall beaccurate it is important that the current in the meter shallbe equal in magnitude in both positive and negative senses,and it must therefore be independent of the characteristicsof the two pentode valves. To achieve this a neon tube isconnected from the H.T. supply to the pentode anodesthrough two diodes. The anode current of whichever ofthe two pentodes happens to be conducting at any giventime then flows through threeparallel paths, namely its ownanode load, the neon tubein series with the appropriatediode, and the meter in serieswith the anode load of the otherpentode. The voltage across theneon tube is constant and indepen-dent of the current passingthrough it, so that the current inthe other two parallel paths,including that containing themeter, remains constant and in-dependent of variations in the

Input I

Input2

AMPLIFIER

AMPLIFIER

pentode anode current, these variations being intro-duced only into the path containing the neon tube.

A block diagram of the whole instrument is shoVfn inFig. 7 and a circuit diagram in Fig. 8, from which it willbe seen that there are two identical amplifying and pulse -forming channels.

Considering one of these two channels, the input is firstamplified by a two -stage amplifier, V, and V2, which hasstable gain, wide frequency response, and is free from phaseshift and distortion. A double -diode limiter, V restrictsthe positive excursion of the amplified signal to a value suchthat the grid of V, is never driven positive with respect toits cathode. The precise level at which this limiting occursis determined by the setting of VR,. This potentiometer -obtains a voltage from the main H.T. supply, this voltagebeing fed through R to the anode of the diode V3b.V51, cuts off as soon as the applied voltage reaches a valuewhich makes the cathode positive relative to the anode.The other diode, V,a, is inverted and connected in parallelwith V35 to avoid a D.C. voltage being established acrossVR, and R13 due to rectification of the signal, which wouldupset the biasing conditions of V,.

V, and V5 comprise a D.C. trigger pair with two stablestates. The control grid bias of V, is set critically byadjusting VR, so that the trigger pair may assume either ofthe stable states with equal ease. This ensures that V, willtrigger on its control grid as nearly as possible at the instantwhen the signal from V35 passes through zero on both posi-tive and negative excursions, the actual backlash beingabout 0-2V.

The anode current of V, is of square waveform of thesame frequency as the input to V,. The differentiation ofthis square -wave current due to the inductance of L,appears at the anode of V, as a voltage having the wave-form shown in Fig. 7.

Vaa is a triode amplifier biased beyond cut-off so thatnegative pulses applied to the grid have no effect, but posi-tive pulses of adequate magnitude receive considerableamplification and appear as short negative pulses, of1.5psec duration at the anode. Similar pulses appear at theanode of V65 and are derived via the amplifying and limit-ing channel associated with the other input. Each of thetwo sets of pulses is time -related to its associated input.

V.7 and V8 are, the D.C. trigger pair used as an electronicswitch for the milliammeter, as previously described.Either valve may be triggered by the application to itscontrol grid of a negative pulse from the anode of theassociated triode. It may also be triggered in the reversesense by the application to its control grid of a positivepulse received from the screen grid of the other valve ofthe pair. The effect is that a pulse at the anode of Va. orVgb not only triggers its associated pentode into a non-conducting state, but also triggers the other pentode intoa conducting state. The time, therefore, that the triggerpair spends in either of its two stable states depends uponthe interval between the negative pulses which are arrivingalternately from the anodes of V,a and Vgb.

Adjustment of the meter current is by control VR whichis set so that the scale reading of the meter is 90° (2mA)

Fig. 7. Block diagram of phasemeter

LIMITER

LIMITER

PULSEGENERATOR

PULSE

GENERATOR

DIS-CRIMINATOR

DC.TRIGGER -

PAIR

D S-CR I MIMA

INDICATOR


AM

PLI

FIE

RLI

MIT

ER

0.1,

F v,,

2200

0

9v

ttsR

icr

R11

2200

2200

C

RO

PE

DC

TR

IGG

ER

-P

AIR

7-7

I.

L., 1

-47

000

hE

F9I R

s

2514

0R

.

Iden

tical

with

the

abov

eA

mpl

ifier

,Li

mite

ran

doc

. Tri9

9er-

Pai

r

Com

pone

nt -

Rnc

ee o

re

R,,,

, VR

,0 C

,01

C00

.7,0

L,01

and

V,g

,-.V

,g,

EF

9I v,00

1,4,

A,,

Imo

C. 10

000

Re

A,.

3.

1000

0

RE

STS

FOR

TO

LE

RA

NC

ES

±1%

±5%

±15

%R

10, n

oR

11, l

itR

27R

28R

29R

30R

37 R9

R50

R58

VR

,R

28

R44

R52 R

All

othe

r re

sist

ors

±10

%

CA

PAC

ITO

R T

OL

ER

AN

CE

S±

10%

± 1

5%

±20

%C

7C

13C

wC

0C

16C

14C

9C

17C

22C

10C

18C

24C

19C

22,

C21

C26

C23

Clo

gA

ll ot

her

capa

cito

rs +

25%

RE

SIST

OR

RA

TIN

GS

4WD

V5W

SW

R10

R7,

107

R53

R34

Re,

110

4R

28R

28R

12, 1

12R

44R

20R

21R

5,R

37R

2.,

Rno

R23

R58

R40

R47

R11

,R

48R

49R

57 RA

ll ot

her

resi

stor

s-4W

CA

PAC

ITO

R W

OR

KIN

G V

OL

TS

150V

400V

500V

600V

C6

C11

C7

C18

C15

C8

C17

C20

Cg

C10

5C

10C

19C

21 C23

All

othe

r ca

paci

tors

-35

0V

A

DIS

CR

IMIN

AT

OR

- A

MP

LIF

IER

1421

2100

A22

2714

0

6J6

A2,

1500 6J

6

A26

Rts

6800 47

000 C,

7

TO

pF

V66

Rm

3

33k0

1006

10

80F

V17

,25

00 R47

47k0

R37

8220

1147

°1:

Rat

2700

821,

0

is IOpF

4700

0

1500

0

Cy

0258

F

A,,

22k0

DC

. TR

IGG

ER

-P

AIR

PO

WE

R U

NIT

R32

1000

85A

2

Rev

erse

Sii

Out

put,,

,/12

2200

Fig

. 8.

Circ

uit d

iagr

am fo

r ph

asem

eter

154

4700

VA

,25

04,0

BA

CK

-O

FF

CU

RR

EN

TG

EN

ER

AT

OR

OC

inF

CiC

a

EA

C9I rz

ko

Ca4

wi:

.001

8F

ee?

..e,

65,/

01A

4-70

in the shunted condition. Control VR, is adjusted so thatthis meter reading is maintained whichever of the twopentodes is conducting.

At very high frequencies, the input signals may be sub-jected to unequal phase shifts due to the limitations of thesignal amplifier and trigger circuits, and this error may beintroduced into the meter indication. The check switchS, 5,2, which operates relays A and B, is a device forinterchanging simultaneously the two amplifying and trig-gering channels one with the other. In this way anyspurious phase shift is re -introduced into the system in areversed sense and the difference in the meter indicationat the two positions of the check switch is equal to twicethe error. The mean of the two indications is the correctreading.

In some applications it may not be convenient toarrange that the inputs to the phasemeter from the voltagegenerators shall have zero phase displacement at the zero -torque condition, and means are therefore provided forbacking -off any initial reading on the meter by injectinginto it n.c. of suitable sense and magnitude. The methodof generating back -off current is shown in Fig. 8. It con-sists of a diode -triode V, the triode section of which isarranged as a Hartley oscillator operating at about 1Mc/ s.The H.T. supply for this oscillator is from the main stabilizedsupply and is compensated for heater voltage variation.Power in the oscillatory circuit is transferred to thesecondary winding of T2 and rectified by the diode of V16,thus providing an isolated source of D.C. VR, gives controlof the magnitude of the back -off current and switchS S, S, provides reversal of the sense of the back -offcurrent in the meter circuit. The third position of theswitch allows the back -off current to be removed entirelywithout disturbing VR,. The amount of back -off currentcan be measured directly and checked at any time whilethe instrument is in use by operating switch Si, 52, S3. S4*

The phasemeter will operate satisfactorily with inputsignals having an amplitude of between 2mV and 80mVR.M.S. Signals of unequal amplitude constitute a possiblesource of error, so that care should be taken that the signalsare equal and as large as possible without exceeding the80mV limit.

Since the phasemeter error is constant, accuracy ofmeasurement can be increased if it can be arranged that thetotal number of electrical degrees recorded is large. So faras the meter is concerned, there is no limit to the totalnumber of electrical degrees which can be recorded, themeter merely repeating its readings cyclically. If the milli -ammeter is used in the shunted condition, the current inthe milliammeter circuit will change from +2mA to -2mAas each successive 360° of phase displacement occurs.There are, however, two objections to operating theinstrument with the milliammeter in the shunted condi-tion; first the fact that the meter will be working on itsless sensitive range, and secondly the fact that phase dis-placements in the region of 0° and 360° will fall in theunusable part of the range. Both these difficulties can besimultaneously avoided by arranging that the phasemeteris used only over the range of phase displacements from900 to 270°, corresponding to a change of the current in themilliammeter circuit from +1mA to -1mA. When thephase displacement reaches 270°, the current in the milli -ammeter circuit then being -1mA, the phase of one ofthe two inputs to the phasemeter is shifted by 180°, sothat the phase displacement again becomes 90° and thecurrent in the milliammeter circuit returns once more to+1mA. As the current in the milliammeter circuit willat no time exceed lmA in either sense, the meter can beused in the unshunted condition and the sensitivity will bea maximum.

In view of the marked advantages of the second of thetwo methods outlined above, it was used as a basis forfurther development, the first problem then being to evolve

a means of shifting the phase of one of the inputs to thephasemeter by 180', as and when required. Such a phaseshift can be most readily achieved by reversing or invert-ing one of the generator outputs, but in so doing it isimportant that certain precautions are observed. In thefirst place, the phasemeter has one of each pair of inputterminals connected to earth so that if the output from thegenerator is a voltage with reference to earth, reversal can-not be obtained by simple transposition of the leads tothe input terminals of the phasemeter. Secondly, inversionwill produce 180° phase shift only if the waveform issymmetrical, that is to say if it does not contain evenharmonics. When the generator output is a voltage withreference to earth, a transformer can be interposedbetween the generator terminals and the phasemeterterminals, and reversal can be effected on the secondaryside of the transformer. The use of a transformer, how-ever, is likely to introduce a phase shift which, while notobjectionable if it were to remain constant, would almostcertainly vary with frequency and introduce an error in thereading of the meter. On this account inversion wasattempted by interposing a valve amplifier between thegenerator terminals and the phasemeter terminals when180° phase shift was required, care being taken in thedesign of the amplifier to ensure that any phase shift whichit introduced did not change with frequency. It was found,however, that the generator output was not sufficientlysymmetrical to produce exactly 180° phase shift by meansof inversion. The idea was then conceived of using asecond generator on one end of the shaft, the two genera-tors being so disposed relative to each other that therewould be 180° phase difference in their outputs. It wasfurther realized that if these two outputs could be com-bined in push-pull and subsequently split again so as toproduce two voltages with reference to earth, anyunbalance of the generator outputs, whether in the formof even harmonics, inequality of amplitude, or phasedifference other than exact 180°, would tend to disappear.The generator outputs were combined and then split againby means of a differential amplifier in preference to atransformer, although it was appreciated that the trans-former would have been simpler and equally effective hadit not been for the phase shift problems which it wouldprobably introduce.

REFERENCEI. FIELD, J. F. The Application of Gas Turbine Technique to Steam Power

Proc. Instn. Mech. Engrs. 162, 209 (1950).

(To be continued)

New Uses for Polytetrafluorethylene (P.T.F.E.)Polytetrafluorethylene (P.T.F.E.) is a resin -like substance

unique among organic compounds in its chemical inertness, itstoughness over a very wide range of temperatures, its excellentinsulating properties and its unusually low co -efficient of friction.

Unfortunately these same properties of chemical inertness andnon -sticking have hitherto presented difficulties of fabricationwhich have in turn limited its application.

Now by newly developed processes The Edison Swan ElectricCo., Ltd., are able to produce P.T.F.E. bonded to metal orrubber, P.T.F.E. bonded fibre -glass laminates, continuouslength P.T.F.E. cylinders and P.T.F.E. beakers for laboratoryuse.

Metal -backed P.T.F.E. will find a number of applications inthe electrical industry. It can be readily fixed to any supportby soldering or mechanical means and the adherence of themetal bond is such that satisfactory hermetic joints can beachieved.

P.T.F.E. bonded with rubber combines the flexibility ofrubber with the complete chemical inertness of P.T.F.E.Laminates of this type make excellent valve and pump dia-phragms, washers, seals and flexible couplings.

P.T.F.E. bonded fibre -glass laminates have excellent elec-trical and mechanical properties which remain unimpaired atextremes of temperature.


Relay Scale -of -Two Circuits(Part 2)

By R. C. M. Barnes*, B.Sc.

Other Circuits with Two RelaysThe remaining circuits with two relays which will be

described do not include a prime pair circuit element toproduce the sequence of operations when the first pulse isreceived. In one type of circuit the B relay is short-circuitedduring the first pulse, and the A relay during the secondpulse, to produce the required sequence. Another type ofcircuit uses relays with balanced windings to prevent Boperating during the first pulse and to release A during thesecond pulse. A third type of circuit uses side -stablepolarized relays so that both relays have two stable condi-tions without the need for holding circuits.

Fig. 10. Well-known circuit with single -wound relay coils

2

Fig. 11. Another circuit for single -wound relays

FIRST PULSE SHORT-CIRCUITS B; SECOND PULSE SHORT-CIRCUITS A

One of the best known scales -of -two'.' (Fig. 10) is of thistype. The sequence of operating and releasing is the sameas before: A operates during the first pulse, B operatesafter the first pulse and A remains operated; A is releasedduring the second pulse and B is released after this pulse.It will be seen that the B contact routes successive pulsesto prevent the operation of B and to release A. The resistorsare of convenient values to limit the current and protect thedriving contact. The first pulse is also routed by the Acontact to operate A. The make -before -break (K) change-over then establishes a holding circuit for A before dis-connecting the incoming pulse. When the pulse ends B isfree to operate in parallel with A.

A.E.R.E. Harwell.

The second pulse short-circuits A. The K contact, inreleasing, connects the incoming pulse to hold B beforedisconnecting the previous holding circuit. After this pulseends B releases. The short-circuit release of A is neces-sarily slow and the need for a K contact makes the circuitunsuitable for high speed relays and S.T.C. midget relays.The single coils and the K contact are suitable for " normalminiature " sealed relays.

A second circuit of this type is shown in Fig. 11 and issuitable for relays with single coils and break -before -makechangeovers, such as the S.T.C. midget relay. The B con-tacts route the first pulse to operate A and prevent B fromoperating. The A contact holds A operated and preparesto operate B when the pulse ends. The B contacts now

(0) ce't,--

Windings of bothrelays opposing

_EL

Fig. 12(a). Circuit for two relays with balanced windings. (b) Modifi-cation of Fig. 12(a).

route the second pulse to short-circuit A and hold Boperated after A has released.

Resistors R, and R2 are chosen to limit the current passedby the driving contact. Resistors Rs and R4 are such that,after the first pulse, the A coil receives not less than therated hold current and B, which is in series with R, andshunted by Rs, receives the rated operate current. R,appears as a shunt across Rs and A after B operates. Underthese conditions both A and B must pass the rated holdcurrent. The circuit has one more contact and two moreresistors than Fig. 10, but may be used with relays whichcannot have a K contact.

TWO RELAYS WITH BALANCED WINDINGS'In Fig. 12(a) both relays have balanced windings (i.e.

windings providing equal ampere -turns). The first pulse isapplied to both windings of B and one winding of A.The windings are connected in opposition so that B doesnot operate. The K contact connects a hold circuit to the


and B2 windings before disconnecting them from theincoming pulse as A operates. When the pulse ends onlywindings Ay and B, are energized and relay B can operate.The next pulse energizes winding Aw which is in opposi-tion to A,. Relay A releases and returns windings A, andB, to the incoming pulse so that A continues to be balancedout and B remains operated until the end of the pulse. Thecircuit has two practical disadvantages. The release of Ais retarded by the presence of a second winding in serieswith the power supply, and the necessity for a K contactand balanced windings restricts the circuit to 3 000 and 600type relays.

These difficulties are overcome in the modified circuit ofFig. 12(b). Here the K contact is replaced by a normalchangeover contact and a rectifier, which maintains theoperating circuit of A during the transit time of the change-over contact. The release of A is improved by adding seriesresistors and operating the circuit from a supply of highervoltage. The balance of the B windings is disturbed bythe forward resistance of the rectifier during the transittime of the A contact, but this effect will, in general, benegligible. The circuit is claimed to count 50 pulses persecond with 3 000 type relays (or 600 type relays with specialwindings) and almost 100 pulses per second with high speedrelays (e.g. Siemens type H96D).

A CIRCUIT WITH SIDE -STABLE POLARIZED RELAYS

The basic sequence demands that relay A should change

Output

- - -

Fig. 13. Circuit for two polarized relays

its state when each pulse is received and that relay B shouldfollow A when the pulse ends. These conditions are satis-fied very simply by the circuit of Fig. 13. The relays arepolarized, i.e. the changeover contacts take up one of twopositions, depending on the polarity of the energization,and they are side -stable, i.e., the contacts remain in theposition to which they are moved. Assume that currentflowing from the positive supply through windings As,- andBw moves the A and B contacts to position 2. Similarlycurrent flowing from the positive supply through windingsAy and B, moves both contacts to position 1.

When the relays are in the state shown, current flows tothe A contact in position 2 through windings Aw and IL,in series. Both contacts are retained in position 2. The firstpulse is routed by contact B, to the A, winding. The currentin winding A, is twice that in Aw and the energization ofrelay A is therefore reversed. The A contact changes overto position 1, but winding B is short-circuited during theremainder of the pulse. After this pulse current flows tocontact A, through windings Ay and B2. The B contactmoves to position 1. The circuit is completely symmetricaland the next pulse restores the relays to the original condi-tion. Outputs may be taken from points x and Y if theoutput circuits are isolated from the scale -of -two byrectifiers as indicated at x.

This circuit does not possess the objectionable feature ofa relay released by a short-circuit or balanced windings so

that the greater cost of polarized relaysjustified where high speed is necessary.

Scales -of -Two with only One RelayThe circuit shown in Fig. 14 is probably

scale -of -two circuit with only one relay.by two changeover contacts 1, and 12. In

(0)

(b)

(e)

WindingsOpposing

Ci

Output

C2

may often be

the best knownIt is controlledthe rest condi-

Fig. 14. Simple circuit for one unpolarized relay

EMI Milli lux decreasing

Fig. 15(a). Circuit with one polarized relay and inductance. (b) Circuitconditions with input contact closed. (c). Circuit conditions after input

contact re -opens

Output

20H 2500Per Section

Flux increasing

.0-30A-

tion, as drawn, capacitor C, is charged and C, is discharged.During the first operation of I C, discharges through wind-ing A,. Relay A operates and holds over its own makecontact. When 1 releases, C, is charged and the conditionof C, depends on the nature of the output load. The secondoperation of I allows C, to discharge through winding A.Windings A, and A, are balanced and connected in oppo-sition so that the relay releases. The relay coil and capa-


citor C2 must be chosen so that the relay does not re -operatewith reversed energization. When I releases, with Areleased, C, is charged and C2 remains discharged. Thecharging currents must be limited by resistors to suit theratings of the relay contacts. The complicated input withtwo changeover contacts limits the usefulness of this circuit.

A more useful circuit, which is controlled by a makecontact, uses one side -stable polarized relay and a chokewith a centre tap (Fig. 15 (a)). The operation of this circuitwill be described in detail with the aid of Figs. 15(b) and(c). Assume that the windings of the relay are drawn sothat current flowing downwards through winding V or up-wards through W moves the contact to the right (to posi-tion 1) and currents in the opposite directions move thecontact to position 2. If the relay is in its rest conditionagainst contact 1 it is maintained there by the side -stablefeature and no current flows in the circuit.

The conditions shown in Fig. 15(b) are produced whenthe input contact closes. Current flows from contact A1,through winding V of the relay and the parallel winding ofthe choke to earth. The increase of magnetic flux in thechoke is opposed by a current induced in the other windingof the choke and relay winding W. Both these currents tendto hold the relay against contact 1.

The flux in the choke decays when the input contactopens, and currents are induced in both windings of the

R42k0

Ill--00011-

Output

F:g. 16. Circuit with one polarized relay and capacitors

choke and relay (Fig. 15(c)) in directions tending to movethe relay contact to position 2. The circuit is completelysymmetrical and the next pulse returns the relay to con-tact 1 in a similar manner. Outputs can be taken fromthe A contacts if the load is isolated from the scale -of -twoby rectifiers as indicated in Fig. 15(a). The circuit isclaimed to operate with an input of 50 pulses per second.

A second circuit with a side -stable polarized relay isshown in Fig. 16. In this case capacitors are used to deter-mine the direction in which the relay moves after eachinput pulse. In the rest condition no currents flow. If therelay is resting against contact 1 the first closure of theinput contact allows current to flow through winding V ofthe relay to charge capacitor C,. There is also a parallelpath through R,. Current flowing in this direction throughwinding 1 maintains the relay against contact 1. C, dis-charges through R1, winding A, and R. when the input con-tact opens at the end of the pulse. Current flowing in thisdirection through winding 1 moves the contact to position2. The circuit is symmetrical and the next pulse returns therelay to contact 1. Outputs can be taken from the A con-tacts if isolating rectifiers are used as shown.

Fig. 17(a) shows a circuit in which there is only one un-polarized relay with a single changeover contact, but whichrequires a choke, a transformer and a driving contactswitching the positive supply. The driving contact appliesthe positive supply during the first pulse and current flowsin the choke L. Rectifier MR, isolates winding A, duringthis pulse. Current continues to flow in L through therelay winding A, and rectifier MR, when I opens at theend of the pulse. The relay operates and current flowingthrough resistor R and the transformer secondary T2, recti-

fier MR, and relay winding A., holds the relay operated.The next closure of 1 finds the original circuit through L

disconnected and current flows through the transformerprimary T, and rectifier MR,. The E.M.F. induced in thesecondary T. is in such a direction as to augment the hold-ing current in relay winding Aw. An E.M.F. is induced in

(o)

Fig. 17(a). Anotherversion of Fig.

circuit17(a).

MR3

(C)

with one unpolarized relay.(c). Further modification of

Output

(b). ImprovedFig. 17(a)

the opposite direction in the transformer secondary T2 whenI opens and the supply voltage is momentarily opposed,so that the relay releases.

A more useful variety of this same circuit is shown inFig. 17(b). Here the three inductances have been rearrangedto be wound on a common core. The driving contact Iis earthy. Current flows through resistor R, rectifier MR.


and transformer winding T, during the first pulse. An E.M.F.is induced in the transformer secondary T, in the non-conducting direction of rectifier MR, so that the relay doesnot operate. At the end of this pulse an E.M.F. is inducedin the opposite direction in winding Ta and the relayoperates. A circuit is then completed through the relaycontact, rectifier MR the relay coil, transformer windingTa and rectifier MR, to hold the relay operated. RectifierMR, and transformer primary T2 are connected in parallelwith MR, and Ti, but in the opposite sense to await thenext input pulse.

R has approximately the same resistance as each trans-former primary winding and current flows in T, and T2when 1 recloses, the resultant change in flux in the trans-former being in the opposite sense to that produced by thefirst pulse. The E.M.F. induced in Ta therefore augments thecurrent holding the relay operated. At the end of this pulsethe E.M.F. induced in T, opposes the supply voltage andrelay A releases. Rectifier MR, opposes the E.M.F. inducedin primary winding T, at the end of the second pulse.

Fig. 17(c) shows a further variety of the circuit in whichthe make contact is free to give an output.

A recently published circuit° (Fig. 18) uses an un-polarized relay and is controlled by a free changeovercontact. Contact A2 provides a circuit to discharge the capa-citor in the rest condition. The capacitor begins to chargeup through both windings of the relay in series when the

+ 35V

Output

270

2

270200µF

+35V

Fig. 18. Circuit for one unpolarized relay

input contact / operates. The relay operates and holds overwinding V. The capacitor is sufficiently large that the volt-age across it has only risen by a few volts while the relayis operating. The capacitor discharges through winding Wafter the relay has operated, but the small voltage appliedto this winding does not reduce the total energization belowthe hold ampere -turns. The capacitor is charged throughthe current limiting resistor when 1 releases.

Current flows through winding W of the relay to dis-charge the capacitor when I re -operates. This current istwice that in winding Av and the relay releases before thevoltage across the capacitor has decreased by more than afew volts. The capacitor charges up through both relaywindings when A, open, but the small voltage applied tothe relay does not re -operate it.

Other Published CircuitsTwo circuits with inherent weaknesses have been pub-

lished. These will now be described and a brief referencewill be made to various scale -of -two circuits which havebeen used as illustrations of the application of algebraicmethods to circuit design.

PUBLISHED CIRCUITS WHICH ARE NOT RECOMMENDEDFig. 19 shows a scale -of -two using four relays" , of which

A, C and D were specified as high speed relays and B wasa multi -contact relay (3 000 type) in order to provide con-tacts in associated circuits. The first input pulse operatesC and A in series. The break contact of C relay preventsthe operation of the slower relay B. At the end of thispulse A holds over the D break contact, C releases, and Boperates. The next input pulse operates D in series with

A, the 500 ohm resistor being necessary to prevent the Ahold contact short circuiting D. When D operates, the holdcircuit for A is broken. After this pulse D and A release,followed by B. The weakness of the circuit is that itdepends on D and A having approximately equal releasetimes. If D releases faster than A it may re-establish thecondition with A holding over the D break contact. Theperformance of this circuit is limited by the operating andreleasing speed of B. Many of the circuits described abovegive a similar performance with only two relays.

Another circuit" (Fig. 20) has two relays. Relay B hasbalanced windings which are used to prevent its operationduring the first pulse. Relay A is released by short-circuit-ing during the second pulse. The first pulse operates A,which holds, and also energizes winding B. The By wind-ing is energized to balance out B. when A operates.

II.

Fig. 19. Circuit with four relays

4 -

Fig. 20. An elaborate circuit with two multi -contact relays

It is therefore essential that A should operate before the Bcontacts break. When the first pulse ends B is energizedover winding /3,, only and can operate. The second pulseis then routed to short-circuit A, which releases, and alsoenergizes winding By, with the polarity which holds Boperated. After this pulse B releases. The momentary un-balance of B while A is operating could be prevented byadding a third A make contact at the point x so thatboth windings of B are energized simultaneously. Thecircuit would then require three contacts on each relay andhas no advantages compared with other circuits which havetwo contacts on one relay and only one contact on theother relay.

CIRCUITS ILLUSTRATING ALGEBRAIC DESIGN METHODSSeveral symbolic methods have been described which can

be used to form an algebraic expression representing a relaycircuit. The behaviour of the circuit can then be revealedby re -arrangement and simplification of the algebraic repre-sentation. Conversely, if the logical requirements are statedit may be possible to construct an algebraic expressionwhich can be manipulated into a form representing a prac-ticable circuit. Montgomerie and Lewis give examples of theapplication of algebraic methods to the design of scale -of -two circuits. It may be of interest to examine the circuitswhich have been used to illustrate these methods, bearingin mind that the principal aim was presumably not so muchto produce useful circuits as to demonstrate the design pro -


cedure (for details of which the reader should refer to theoriginal papers).

Montgomerie" uses a method which takes into accountthe finite transit time of relay contacts to derive the circuitshown in Fig. 21(a). The impulsing relay I has a change-over contact and a late break (Y contact) which breaksafter the changeover action is complete. An alternativeform (Fig. 21(b)), combines the make from the changeoverand the late break to form a make -before -break contact.

8 8

( a ) ( b)

Fig. 21. Examples of an algebraic design method

(a) ( b)

Fig. 22. Circuits deve1oped from l ig. 21

( a)

(b) (C)

Fig. 23. Examples of another algebraic design method

2

o

Elliott " shows that a further simplification can be appliedto obtain expressions representing the circuits of Fig. 22(a)(corresponding to Fig. 21(a) and Fig. 22(b) (correspondingto 21(b)). The requirements for the impulsing contacts inFig. 22(a) are formidable unless it can be assumed that thetransit time of the I changeover is small compariththe release time of A-, in which case the I break Mactneed not have a late action. In Fig. 22(b) the impulsingcontacts appear to be less complex but, unless it can beassumed that the I break opens before (or not long after)the K contact closes, relay B may be operated prematurely.This sequence cannot be guaranteed with standard relayadjustments.

If the complexity of a circuit is measured by the numberof terminals which are interconnected it is remarkable that

Fig. 1(a) has 16 interconnected points and Fig. 22(a) hasonly 14 interconnexions.

Lewis" uses a different method which does not allow forthe finite transit time of the I contacts and derives thecircuit of Fig. 23(a). If the I contacts are redrawn as make -before -break changeovers this circuit is practicable and hassome similarity to Fig. 1, although using more contacts.He further simplifies this into the forms of Fig. 23(b) and23(c) which will be seen to be identical with Fig. 22(a) andsimilar to Fig. 22(b), respectively, if the sequence of opera-tion of the I contacts is corrected.Acknowledgments

The author is indebted to his colleagues in the Auto-matics Group for their help in collecting scale -of -twocircuits from various sources, and to the Director, A.E.R.E.,for permission to publish this article.

REFERENCES7. FROST, G. R. Counting with Relays. Trans. Amer. Inst. Elect. Engrs. 68,

587 (1949).8. SVVIRE, B. E. Relay Scaling Circuits. J. Sci. Instrum. 29, 339 (1952).9. Comm, B. D. A Single Relay Scale -of -Two Counting Unit. J. Sci. Instrum.

29, 270 (1952).10. DEACON, E. L. Two Types of Sensitive Recording Cup Anemometer. J. Sci.

Instrum. 25, 44 (1948).II. MCCALLUM, D. M., SMITH, J. B. Feedback Logical Computors. Electronic

Engng. 23, 458 (1951).12. MONTGOMERIE, G. A. Sketch for an Algebra of Relay and Contactor

Circuits. J. Instn. Elect. Engrs. 95, Pt. 3, 303 (1948).13. ELLIOTT, R. L. Discussion on above. Proc. Instn. Elect. Engrs. 96, Pt. 3,

166 (1949).14. LEWIS, I. A. D. A Symbolic Method for the Solution of Some Switching

and Relay -Circuit Problems. Proc. Instn. Elect. Engrs. 98, Pt. 1, 181 (1951).

Marconi Image AmplifierA New Development in X-ray Diagnosis

This unit manufactured by Marconi Instruments Ltd. is aconsiderable development in the field of diagnostic radiology:Fitted to the screen frame of the Marconi Tilt Table, it pro-duces an Image, available in the normal viewing positions, atone -tenth of the current required with conventional fluoroscopicscreens.

Among the advantages offered are greater detail, reduction ofdark adaptation, due to the brighter image, and reduced radia-tion. Details which are present but not discernible on the con-ventional fluoroscopic screen are rendered clearly visible andcan be recorded directly from the output phosphor by eitherstill or cine camera using normal screening current. The longperiods of dark adaptation necessary for conventional screen-ing are largely eliminated with this brighter image. Amplifica-tion of the image also permits faster examination with low X-ray intensity, thus reducing the amount of radiation absorbedby both patient and operator.

The optical system not only serves to reorient the image, butalso aligns it correctly with the patient. The viewing mirror,which provides binocular vision, is so mounted that a radio-logist of any stature may view the image in perfect comfortregardless of the angle to which the table is tilted.

Normal spot -film technique can be used with the ImageAmplifier connected to the screen frame and the counter-balancing suspension enables the entire Image Amplifier to bepushed up to the ceiling for parking when not in use. TheMarconi "500" Tilt Table has a readily removable fluorescentscreen with specially designed fittings for rapid substitution ofthe Image Amplifier. The use of the Image Amplifier, however,is by no means limited to this particular table and it may bereadily adapted for use with tables of other manufacture, andmay have many applications in industrial radiography.

Image Amplifier operation entails the substitution of anelectron accelerator tube for the normal fluoroscopic screen.

This tube has its own 5in diameter fluorescent surface uponwhich the X-rays passing through the patient will impinge.The fluorescence excites a photo -electric plate and the electronsemitted are accelerated by a high potential applied to the tubeby an external power source. A system of electron lensesfocuses the inverted image on another screen lin in diameter,where the combined effects of acceleration and minificationgive a considerable increase in brilliance. The optical systemthen reorients this image, which is viewed in a convenientmirror, at its original size.


"Starved Amplifiers "By G. E. Kaufer*, M.S.

This article describes a type of D.c. amplifier, known as a " starved amplifier", in which very lowanode and screen voltages are used. The design of this type of amplifier is considered in some

detail, together with its advantages and possible applications.

PRIOR to the introduction of so-called " starved "methods of valve operation, the two most widely used

single valve high gain D.c. systems were the application ofa high voltage power supply with correspondingly largeanode load resistors and the series connexion of a dualtriode which, when operated properly, yields a gain approxi-mately equal to that obtainable from a single pentode. Bothof these systems have their shortcomings and it is pre-dicted that, as more engineers become familiar with starvedamplifiers, this circuit will take a leading place among theolder, more standard modes of operation.

The chief drawback in employing a large load resistorand attempting to operate the valve so that its mutualconductance is large lies in the power supply requirements.If normal valve operation is contemplated (which willyield mutual conductances in the order of 4mA/V forthe average pentode) with the hope of securing a stagegain approximating the product of gm and R., it is truethat this gain will continue to rise as the load resistor (Ra)is increased, but the anode supply voltage will increaseproportionately. Reasonably high values of gm are obtainedonly with substantial valve anode currents and Ohm's lawimposes its limitations on this circuit. A definite advan-tage which must not be overlooked in passing, however, isthe fact that, since the quiescent potential appearingbetween anode and cathode of the pentode is in the orderof that found for normal valve operation (100 to 400 voltsfor most receiving type pentodes) the anode swing canbe made large. This circuit is capable of handling afairly large input signal and yet will deliver a large un-distorted output voltage. Operation is reliable and stable,as the valve is operated under the normal specified condi-tions. As a D.C. amplifier, the usual coupling problems arisesince the anode is at a fairly high D.C. potential withrespect to cathode. Design is simple and foolproof, involv-ing the selection of a suitable quiescent point, determiningthe required load resistor knowing the desired stage gainand the mutual conductance at the quiescent point selected,and then plotting the load line on the standard anodecharacteristics (for the correct screen grid voltage) for theRa chosen from the knowledge that the slope of this lineis equal to the reciprocal of R. and it must pass throughthe given quiescent point. The intersection of this loadline and the abscissa ib = 0 gives the required anode supplyvoltage.

The second method (see Fig. 1), even more popularthan the first because of its added feature of providingdual inputs while requiring nothing in the way of extra-ordinary components or voltages, yields a gain (from g,to the output) approximating gmRa. Incorporating a dualtriode, it combines the high gain and stability of a pen-tode amplifier with the low noise characteristic of a triodeamplifier. This circuit is commonly employed as a mixerand amplifier at radio as well as at audio frequencies.Stage gains are not " high " in the true sense of the wordsince, as the mutual conductance of a triode is approxi-mately of the same order of magnitude as that of apentode (gm is determined by grid -cathode electrodespacing and other features of tube construction) the mag-

* Columbia University, New York.

nitude of load resistance again imposes the limitationson the gain obtainable. The gains of both inputs are farfrom equal. Care in selection of valve types in the designof the cascode amplifier is necessary. Caution must beused since the heater -cathode potential of one section ishigh and the valve ratings must not be exceeded. Types6BQ7 and 6BK7 have been developed especially for thisapplication, incorporating a high gm, a 200V peak heater -

e2

fi

Fig. I (left). Cascodecircuit

Fig. 2 (below). Ex-perimental high gain

D.C. amplifier

Cc determines lowfrequency limit.

HT+

cathode potential (as high as 300V under special condi-tions of operation), low interelectrode capacitances and aninternal shield for circuit isolation. When used as a D.C.amplifier, the usual coupling problems exist since the valvesdraw normal current and the quiescent points are standardin every respect.

A circuit, too recent to be considered at this point sinceit is still in the early stages of development, has cometo the author's attention. It is capable of producing verylarge stage gains (in the tens of thousands) by employinga second valve as a large dynamic anode load for the highgain stage. Referring to Fig. 2, V, reflects back into theanode of the preceding stage a load impedance equal tothe actual load resistor (R.) multiplied by a factor equalto the reciprocal of (1 -K) where K is the gain of V2.


The ideal load for starved amplifier operation is thusprovided while still maintaining a high gm, as valve poten-tials are standard. By nature of its operation, however,this circuit does require two valves per stage of gainalthough its phase shift and other characteristics areseemingly equivalent to that of a single valve. While thiscircuit works well for audio frequencies, further experi-mentation along the line of coupling methods is necessary(neon bulbs are used at present) until it can be made toperform adequately and reliably on direct current inputsignals.

In the circuit illustrated in Fig. 3 E2 < Ebb/10 and theload resistor is greater than one megohm. Such a circuit,known as a " starved amplifier ", is capable of producingthree or more times the gain btainable from the samevalve wired as a conventional amplifier, even though themutual conductance of the starved valve is considerablydecreased. Although certain disadvantages accompany thismode of operation; they are far outweighed by the featuresgained.

ADVANTAGES

Starved amplifiers have many distinct advantages which,when fully realized and utilized, will make this circuitoutstanding in its class. With this mode of operation, onecan obtain stable, high gain amplification, requiring fewervalves for a given gain than with other conventional cir-

HT.

H

Fig. 3. Basic "starved amplifier" circuit

cuits. The circuital phase shift is therefore reduced (amaximum of 90 degrees phase shift per stage of amplifica-tion) and hence more feedback can be applied to thecircuit for stability. In fact, such a circuit is ideally suitedfor applications where a high base gain is desired for properoperation and then an overall feedback loop is closed toget the nominal gain, bandwidth, stability, etc. Internalfeedback loops are readily added to this circuit, the com-monest forms consisting of screen voltage control. Inextreme cases, the signal may be fed into the cathodeof the starved stage with feedback loops encompassingboth screen and control grids. Because of the high loadresistances employed, loading effects of the following stagemay be severe unless a cathode -follower is resorted to.The starved amplifier -cathode -follower combination, how-ever, has the added feature in that, while consisting of acomplete and stabilized unit (internal feedback loops fromcathode -follower load to screen and/or control grid ofstarved stage), it is capable of delivering power to anexternal load, while at the same time preserving the highfrequency response of the amplifier (which, incidentally,is poor to begin with because of the high resistancesemployed).

All D.C. amplifiers are inherently susceptible to driftbecause a slight change in grid to cathode voltage in thefirst stage (due to a slight variation in anode supply orheater voltage, resistor drift, or valve unbalance) is ampli-fied in succeeding stages providing a large change inoutput voltage. In starved amplifiers, all the gain is con-centrated in a single (or comparatively few) stage, therebyconfining all minor voltage variations which will have any

effect to the input to this one stage. Since the aforemen-tioned is true, if that stage is stabilized, the entire amplifieris stabilized.

Throughout this discussion, it must be borne in mind thatthe starved amplifier is basically a direct coupled amplifier,lending itself admirably to this application. Problems ofinterstage coupling, the scourge of D.C. design, are reducedto almost nill, since the D.C. voltage appearing on the anodeof the starved stage is quite low and can easily be fed intothe grid of the succeeding stage with few attendantdifficulties.

Multiple stages of starved amplification are also easyto come by if the anode load resistors are reduced to morenominal values in all stages following the first. The neces-sary decoupling for three or more stages may be madequite thorough and compact by connecting a nin resistorby-passed with a 0.05p.F capacitor in series with the anodeload to the first stage (or first two stages as the case maybe). The reduction in physical size and cost of the de -coupling capacitor is made possible by the large valueseries resistor employed. As the current consumed by the

R.

i'-ît-i§"aaZw._< i6Nu.4(in

tli

1.4

Q,

0

9r,

'._.ocIJ

-Z

z1-a2°4 o-.,

0

g

.......us0z?<(01-

0z

Ece-.£62=-5VEss=twe

0.75V

7mVtype 6SG7

ams

I.5mr,

20M0

,ftaI-

'8I _

0 ( 4

0. 10 20 30 40 50 60 70 80D.C. ANODE CURRENT (IsA)

Fig. 4. Variation in valve parameters as a function of anode current

input starved stage can be made quite low (the valve isrequired to handle only a small input swing), the dropacross the series element of the filter is not prohibitive.

Mention must be made of the fact that a negative H.T.supply is not required for normal operation of a starvedamplifier stage. Power supplies employed are standard inevery respect. A further saving can be effected in the supplycomponents since current consumption is reduced by thismethod of operation.

When the remaining features of, (1) inexpensive designwhich leads to compact packaging due to the minimumnumber of circuit components needed, (2) long valve lifedue to the low voltages on the elements and the sub-sequent low current drawn from the cathode, and (3) thepossibility of eliminating all effects due to electrostatic andelectromagnetic pick-up on the grids of the high gain stagesby special design of push-pull circuits are considered, onecan readily realize the large number of applications ofthe starved amplifier, some of which will be discussedlater.

TheoryFor a pentode with high load resistance, gm decreases

with increasing anode load if the supply voltage is keptconstant. To raise the gain of the stage, one must increase


the anode resistance of the valve, since gmra. This canbe accomplished readily by lowering the screen voltage.The starved stage thus obtained will then be found toexhibit a higher gain characteristic than that of thepentode with normal screen voltage, high load resistor andthe same anode supply voltage. The principle underlyingthis method of operation is that, although the transcon-ductance is decreased to a small fraction of its normalvalue, the anode resistance increases at a much greaterrate over a portion of the operating curve and hence theµ of the valve increases. As can be seen from an examina-tion of a typical ,u//a. curve (see Figure 4), this analysiscannot be extended to include continuingly increasingvalues of load resistance, as a point is reached at whichthe ,LE of the valve will drop off rapidly and continue todrop at a fast rate as valve current is further decreased.

In

O

Valve type 6SG7£7= 5Volts

LE- 90Vr'

El - 6.3V

- 1.4 - 12 - O.6 -05CONTROL GRID VOLTAGE (V)

8

0

O

35

30ton

25mrnz

200

15 CI-()C

10 ;:31

rnz

&--o-sy- Solid lints

r, -Dashed lines

.E- -0-6V

-0 7V

o E--O6Va- -0-

E, 0 BV

-a 1.0Vo E,- Gin, E, -- 1-6V E-, -1-2 Vr -----r- -1-----kt---- ..- 14V

20 40 60 80 180

e -07Vo.

ANODE VOLTAGE tv)Fig. 5. Static characteristics of 6SG7 for screen voltage of 5V

This illustrates the fact that there is an " ideal " operatingpoint for each valve, one which will yield a maximumgain for a given set of operating conditions (for a givenscreen and anode supply voltage, there is a definite valueof anode load resistor which will give maximum stagegain).

It is not possible to maintain zero grid current ina D.C. amplifier stage in which anode current is flowing.The grid current is a function of the anode current andmay be made relatively constant by operating at lowanode levels. The starved amplifier circuit fully utilizesthe constant grid current feature as low anode current isinherent in its design. Reference to the curves found inthis article indicate the validity of the aforementionedstatement where operation does not permit the anodecurrent to exceed 50i.tA (quiescent points are usuallychosen well below this figure).

Valve DataBefore one can begin to consider the design of a starved

stage, one must first become familiar with the orders ofmagnitude of the valve parameters and their manner ofvariation under these special operating conditions. It isnecessary to recall at this point that a starved valve must,by definition, satisfy two stringent requirements: thescreen voltage must be less than 10 per cent of the anodesupply voltage and, the current which would flow whenthe valve is connected as a diode (all grids connected tothe anode) must be 1 000 or more times larger than theload current when the valve is wired as an amplifieremploying a load resistor and the same supply voltagesource.

The initial procedure is therefore apparent. Since valve

Eb.. 10V

Valve type 65G7E52 10VOItS

if, 62V

10071

z80 0

60

inin

zo

-22 -1.8 -1.4 -1.0 -06 oCONTROL GRID VOLTAGE ( V)

a.

I-

Qccucc

(3

9°)_80

O

IbSolid lines-Dashed lines

Ec- - 05V° 08V

N, `

4=-0-6V

&- -0 -6V

2.2V

E= -1.0V

-1.2y

E I 4VI.6V

-1111V

O 40 60 BOANODE VOLTA GE t14

Fig. 6. Static characteristics of 6SG7 for screen voltage of 10V

parameters for the low operating potentials used are notnormally supplied, they must be determined (at leastapproximately) by the designer. Typical curves for thetype 6SG7 octal and the type 6AG5 miniature pentodeshave been obtained by the author (see Figs. 5, 6, 7 and 8)and are reproduced here for convenience. It it necessaryto differentiate between the A.C. resistance and the D.C.anode resistance, two entirely different quantities. For agiven operating point, this latter value is equal to thereciprocal of the slope of the line joining the origin andthe point in question on the anode characteristics of thevalve (see Fig. 9). To illustrate this difference morestrongly, it may be stated that under certain conditions ofstarved operation, the A.C. anode resistance may be of theorder of 401\411 whereas the D.C. value is approximately1MSZ.


co

0

QO

Valve type 6AG54-92 IOVOitS

_s E= 0

Analysis of ResultsIt is interesting to note that, while five valves of each

type were tested, the resulting data obtained from eachdiffered greatly. In an effort to correlate this discrepancywith a characteristic of the valve which can be measured

....., E= -02VI -

Id -';1'-ZiaCC a.CC .....O I -u z /b - Solid lines

0 M .tic .,, _ Dashed lines2 CC (,-6-3Vn

u_a DO ag . under normal operating conditions, all valves were firsta c. 'o .I- z . checked in an emission type valve tester and were found to

6z, a ... .4=-04V indicate on exactly the same portion of the meter

E= -02V scale. The next test was that of mutual conductance, this-- -\.___, quantity being measured on a commercial dynamic valve0' 5 tester. In this respect, a difference in readings wasobtained and it was found that a definite correlationpattern resulted, as can be seen from the tabulation of

E,=-Cr6V results in Table 1 for both 6SG7 and 6AG5 valves.el 0 Examination of the data shows that in all cases, as the

E, =-0 4VE, -0f1V

mutual conductance of the tube as measured under nor-mal operating conditions is increased, the quiescent anode

O .E, I v current under starved conditions of valve operation is0 20 40 60 80 100 decreased for a given anode voltage. This is of interest in

ANODE VOLTAGE (v) that a given set of curves for starved operation can beFig. 7. Static characteristics of 6AG5 for screen voltage of 1()V adapted (qualitatively speaking) to other valves of the

same type or possibly even of different types (providedthe normal operating conditions are similar) by a simple

Fig. 8. Anode and screen current/control grid voltage formeasurement of the mutual conductance on a reliable,standard valve tester. There is thus a method of circum-

r venting the " critical " aspect of starved circuit design,/ since matching of valve gm's under normal operating con-/ 8

.ow

A n

ditions is equivalent to matching them under actual

P coI conditions of starved operation.Valvetype 6AG5 i 0

zo in The magnitude of the space current in a pentode isri

odF o 0

rx("c' ax

gr'''' 6 2A?4z

6,...-'

no0,->

E93= OVEg2.= 10VEt, =30VEt =6-3V

-2.2 -2-0 -1.6 -12 -0.8 -04CONTROL GRID ( V )

Ev= OV4-92' I OyE, =30VE, =4-5V

2.2 -20 -I.6 -1.2

6AG5

1-92 &lb /Eb( coincident

curves)

z$O

mcrt.

II. 7)CO rn

zN,

-

-043 -0.4CONTROL GRID ( V )

Fig. 9. Graphical determination of anode resistance

TABLE 1

6SG7 6AG5

MUTUALCONDUCTANCE

ANODECURRENT

MUTUALCONDUCTANCE

ANODECURRENT

(mA/V) (µA) (mA/V) ( µA)3.180 50 4.080 303.100 77 4.000 332.910 90 3.930 1162.870 180 3.700 2002.840 330 3.360 410

determined almost entirely by the control grid and screengrid potentials. The anode potential determines only whatfraction of space current is transmitted to itself. Itdoes, of course, have a second order influence upon theanode current, with the result that lb rises slowly as theanode voltage is increased. Thus, as can be seen by refer-ring to the anode characteristics, all of the curves aresimilar in shape and differ only in scale. The spacecurrent (see Fig. 10) is even more constant with anodevoltage than is the anode current. The only departurefrom near constancy occurs near zero anode voltage.Here the space current. increases by about 20 to 40 percent as the anode voltage is increased to about half of thescreen grid potential. This increase in space current occursbecause there is a change in the space -charge conditions


around the screen grid as the condition of reflexion ofelectrons from the anode changes to one of transmission.

Although not proven here, use can be made of the factthat the suppressor grid is able to control the fraction ofthe current transmitted past the plane of the screen gridthat goes on to the anode. When the suppressor is at alow potential relative to the anode and the screen grid, asit usually is, it can sort out the electrons having a largecomponent of energy directed towards the anode fromthose which, because of deflexion on passing close to ascreen grid wire, have a lower component of anodedirected energy. The anode voltage is moderately sensitiveto suppressor grid voltage and the suppressor is readilycapable of completely cutting off the flow of anodecurrent.

The use of a positive suppressor potential will giveconsiderable sharpness to the shoulder of the anodecharacteristics. An important fact to note in connexionwith this is that for negative suppressor voltages theanode resistance decreases with increasingly negativeapplied voltages. This is evident from an inspection ofthe anode characteristics (Fig. 11). The reverse effectis true to some extent, and hence slightly positive sup -

4'

fg3.=

EConstant

-4

Ey

Fig. 10. Space current

pressor voltages offer additional possibilities for obtaininga higher gain per stage.

Another fact worth mentioning at this point in con-junction with the valve characteristics is the rather highcontrol grid current flow which presents additionalproblems and must be considered in the design of a starvedstage.

Design ConsiderationsPerformance to be expected from a given design must

be viewed with caution due to the considerable differ-ences between valve types, the critical nature of theoperating voltages where maximum gain is desirable, andthe low operating currents involved. An approximatedesign may be carried out on paper, the final adjustmentsbeing made by trimming or adjusting the screenvoltage of the unit after construction has been completed.Certain items must be kept in mind while determiningcomponent values and circuit voltages and a typical designprocedure would be somewhat as follows assuming theproper characteristics for the valve type selected are avail-able (if a stage gain not in excess of one thousand isdesired, the graphs included in this article may be utilizedas a first approximation. These curves were obtained froma type 6SG7 valve with a normal mutual conductance of3.15mA/V):

1. From the µ//b curve, select a quiscent anode currentwhich lies slightly to the right of the highest peak. (If alower stage gain may be tolerated, select an anode currentsuch that the p. of the valve remains approximately con-stant as lb is varied slightly to either side of the quiescentpoint.)

2. Determine gm of the valve for the anode currentselected above by referring to the girl lb curve.

3. Choose a suitable load resistor (usually from 3 to20MC2) from a knowledge of the desired stage gain andthe approximate relationship: Ra=K/gm (which is applic-able when the anode resistance is high compared to theload resistance).

4. For a given anode supply, draw a load line on theanode characteristics, selecting two sets of values for endpoints such as: (a) /.=Ebb/R., Es -=0;

(b) /' 9Ebb/ 10R.; Eb = Ebb 10.5. Knowing the anode current, locate the quiescent point

on the graph and read off the bias voltage. At this pointthe anode current or load resistor may have to be revisedif the bias is found to be too low (not negative enough).

cP

.4

O

0A{ E, - 0

E92 -.30

-20

ti

E93

Fig. 11. Anode characteristics

O

6. A suitable method of biasing must now be selected.From the E0/la curve, note the grid current flow for thebias voltage determined above. If it is zero, the bias mustbe obtained by inserting a resistor in series with thecathode of the valve such that Rk=Ec/(/b+/2). If adefinite value of grid current flows, economy may warrantthe utilization of the grid resistor as the biasing device(rather than employing a transformer input or low resist-ance grid leak and cathode biasing), and this resistor mustbe chosen such that Rg=Ec/Ic.

The advantage of cathode bias is that grid current flow,with its inherent distortion of the signal, can be eliminated.Select a high enough negative bias so that the grid currentis zero for quiescent operating conditions and for therange of grid swing in question (which is usually less thanfive millivolts). This assures a more stable design and lessdifficulty is encountered when valves are replaced.

7. Design the following stage, preferable a cathode -follower for minimum loading (the anode load of thestarved stage acting as the grid leak for the cathode -follower), to provide the desired screen voltage from acathode divider. If this voltage source is made variableto a slight degree, any design errors can be compensatedfor in the completed circuit by making a slight adjustment


at this point. This method of securing the screen gridvoltage also provides for the necessary stabilization of thestage.

It will be found that the screen voltage influences thelinearity of the stage to a large degree. When substantialanode swings are involved the screen voltage must beadjusted with this fact in mind; optimum voltage beingabout 80 per cent of the quiescent anode voltage.

Factors which should not be overlooked in this designinclude:

1. Bandwidth is exchanged for gain, the frequencyresponse of the stage decreasing with increasing anodeload resistance (upper frequency limit is of the order of2kc/s for a 15M52 load). Another limitation imposed onthe magnitude of the load resistor is that it cannot be madetoo high since it is the grid resistor of the following stage.

2. If desired, a compensating network consisting of aparallel RC combination may be added in series with thegrid of the starved stage to prevent positive grid operationand high frequency oscillations. If low frequency opera-tion only is desired, a small by-pass capacitor (10 to 50pF)from the anode of the starved stage to earth will helpimprove the stability of the system.

3. In critical systems an internal gain control may bedesired to compensate for valve replacements. If highquality components are used in the networks which deter-mine the operating potentials of the starved stage, littledifficulty should be experienced with gain variationsduring the life of the valve.

4. With both internal and external feedback loopsapplied, reliability of circuit operation is quite good. It isnot possible, however, to cancel drift due to variation infilament potential with inverse feedback. A regulatedfilament supply or auxiliary valve cancelling circuit mustbe employed for this purpose where extremely high gainand critical circuits warrant its use. For oxide coatedcathodes, a 10 per cent increase in heater voltage is thesame as a cathode -potential decrease of about 0.1V.

5. In cascading stages for high gain, it must be remem-bered that the ultimate gain attainable is limited by theinherent noise of the system as well as problems of in-stability. As will be shown in the following section, theequivalent noise voltage is higher for starved operationthan for normal operation of the same tube.

VALVE NOISERandom noise similar in character to that produced in

a resistor is generated in valves as a result of irregularitiesin electron flow. The equivalent grid resistance Re,representing the noise of a negative -grid pentode ampli-fier is given approximately by the relations:

/b ( 2.5 20/2) 2.5Igm2 = r, +8gmHReg -

lb +12 \ gni

Using the latter relationship, the relative noise for normalagainst starved operation of a type 6SG7 pentode can becomputed as:

Normal operation:Ebb = 250VE, = 125V IZ

Ib = 11.8mA= 4.4mA

gm = 4.7mA/V IB = 16.2mA

47002+10-6 \

2-5 11.8

16-21+ 4.4 x 103)1

Req =k 4700

= 3 30052

Starved operation:Eb = 50V Is = 29.3µAE, = 5V I, = 6.0µAgm = 0.125mA/V I. = 35.3µA

Req =2.5 ( 29.3 +8( 6 x 10-6 )1

= 22 960E2125 x 10-6 35.3 125 x 10-6

The equivalent resistance calculated for normal operationcorresponds to a noise voltage of 0-53p.V, whereas that forstarved operation is equivalent to a noise voltage of1.4uV. The latter operating condition thus increases thenoise by a factor of approximately three.

Applications1. Pre -amplifier for use with low gain amplifiers and

magnetic direct writing oscillographs (current models havea frequency response relatively flat from D.C. to 100c/sand are ideally suited for use in the medical field for themeasurement of brain, heart and nerve potentials in themicrovolt range).

2. Amplifier for use with magnetic pen -motor.3. Transient recorder amplifier for low frequency

phenomena.4. Photocell amplifiers.5. D.C. servo -amplifiers.6. D.c. valve millivoltmeters and microammeters.

ConclusionA starved amplifier does not employ any new or

unusual circuit components to achieve its relatively highstage gain. The circuit is basically simple, the essentially" new " aspect involving the investigation into the methodof variation of the valve parameters at low anode andscreen voltages. Further exploitation of this circuit willundoubtedly lead to the manufacturing of valves especiallydesigned for this type of service, alleviating many of thecurrent disadvantages restricting its use.

BIBLIOGRAPHYI. VOLKERS, W. K. Ultra High Gain Direct -Coupled Amplifier Circuits.

Paper presented at the I.R.E. 1950 National Convention.

Communications in the AntarcticWireless reception is notoriously bad in the Antarctic. The

noise level is high, there is a great deal of static, and in thewinter the aurora australis causes heavy interference. Despitethese difficulties a recent expedition based at Hope Bay mNorth Graham Land, some 700 miles to the South East ofCape Horn, was able to maintain close radio-communicauouboth with the sledge parties operating from the base and withother expedition bases in the Antarctic. The sledge parueswere equipped with Services Type T68 transmitter -receivers,and a BRT 400 communication receiver, made by The GeneralElectric Co. Ltd., was used at Hope Bay.

The expedition forms part of the Falkland Islands Depend-encies Survey, which exists for the purpose of making abiological, geographical and geological survey of Graham Landand the neighbouring regions. In the course of the surveybases have been established at various points and sledgeparties go out from these centres to survey the surroundingterrain. From Hope Bay such parties operate up to 300 milesfrom base in the winter when, though radio reception is moredifficult, conditions are more favourable for long journeys thanin the summer.

Radio communication is essential for relaying weatherinformation back to the Falkland Islands for requestingsupplies and for similar purposes.

The Hope Bay had to relay three hourly weather observa-tions made by the expedition to Port Stanley where they wereincorporated in a forecast for shipping in the South Atlantic;frequencies of 4.4, 5.8, 5.9 and 7.3Mcis were used for thesetransmissions. The Hope Bay base was also in contact withother stations in the Falkland Islands, Deception Island,Admiralty Bay, Port Lockroy, the Argentine Islands andSigny Island, using frequencies of 1.6, 2.2, 4.4, 4.7 and3.8Mc/s. In addition, the communication receiver was usedfor entertainment and the expedition was able to pick upbroadcasts from England.


LETTERS TO THE EDITOR(We do not hold ourselves responsible for the opinions of our correspondents)

A Transistor Performing the DualFunction of Rectification and Ampli-fication for Chemical Analysis at

Radio -FrequenciesDEAR Snt,-The employment of con-

ductimetric analysis now covers quite awide commercial field. For example itis used for ascertaining the percentage ofwater in alcohol. In botany and agricul-ture to determine the acidity or alkalinityof soil. Leather tanners use it to deter-mine the presence and quantity of acidin tan liquor. It is employed also for theanalysis of wine and beer. To estimatethe acidity of fruit and fruit juices. Tocompare and measure the concentrationof solutions and for many otherpurnoses12.

When such work is carried out by rec-tified radio -frequency it is essential touse very small currents to avoid any

F:g. 1 (above). The R.R.F. method

Fig. 3 (below). GET 1 transistor graphs.Curve A plotted with milliammeter in collectorcircuit (resistance of meter = 300E2). Curve Bplotted with meter removed, i.e. with no loadin collector circuit. Curve C current consump-

tion in collector circuit (in milliamps)

24

-21

1w -18

-15

4_J0I-

12

cc 90

Ls)

J 60

,

- 31,5

Micro -Ammeter

(0-500µA)

Fig. 2. The transistor circuit

detectable rise in the temperature of thesolution. In the case of the author'sR.R.F. method where a conductimetrictube is used it is usual to work with cur-rents not exceeding 60µA.

The method is illustrated in Fig. I.Briefly it is as follows : By means of asyringe S a sample of the solution isdrawn up the conductimetric tube T.(This is a glass tube fitted externally withtwo metal electrodes E and E'.) A radio -frequency current controlled by a coup-ling capacitor C is fed to the upper elec-trode E, a displacement current passesthrough the glass down the liquid columnand out via the second electrode E'. Itis then rectified by means of a crystaldiode R. and the rectified current isregistered by means of a zero -shuntedmicroammeter' M.

It occurred to the writer that it mightbe possible to employ a transistor in place

MILLIAMPERES FED INTO COLLECTOR CIRCUIT FROM H.T. SUPPLY ( Curve c)0 .1 02 0.3 0 4 05 045 07 ol (J.9 I. 0 II iv 1 J I4 1 b 10 1./ I15 ry :d.c

I-A c

II A and B= Amplification. Current Consumption

14eO 50 100 150 200 250 300350400450 500

MICROAMPERE DEFLEXION CURVES(Curves A -and B)

of a diode using the emitter to base asthe rectifier and to obtain an amplifiedcurrent from the collector circuit.

As anticipated emitter to base gaverectified R.F. current readings compara-ble to those obtained by the originalgermanium diode. Deflexions of fromM) to 100µA were obtained for aN/400 Kcl solution with only quite aloose coupling to the oscillator.

Fig. 2 shows the transistor circuits.With the microammeter M placed inseries with the emitter the couplingbetween the oscillator and the conducti-metric tube was adjusted to give a de-flexion of 50µA for N/400 KCl andset permanently at that adjustment. Theconductimetric tube was then emptied.

The meter was removed and placed atM in the collector circuit, and afterclosing switches H' and H the zero -shuntwas adjusted to return the meter deflexionto zero. Samples of the solution werethen drawn up the conductimetric tubeand the deflexions were noted for 1.5, 3,6, 9, 12, 15, 18, 21, and 24 volts negativeH.T. applied in turn to the collector. Ineach case the meter deflexion was read-justed to zero by zero -shunt while thetube was empty and before the readingwas taken.

When a milliammeter (having a resist-ance of 300 ohms) was included in thecollector circuit in order to ascertain thecurrent consumption (see curve c (Fig. 3))curve A was plotted.

When the milliammeter was removed aconsiderable increase in amplification wasobtained (see curve B (Fig. 3)). By employ-ing a transistor in this manner meterdeflexions up to 400 or 500µA can beobtained, while still no more than 50 or60µA are passed through the solution.

The results obtained also suggest thepossibility of operating a relay for thecontrol of liquid flow', by the employ-ment, if necessary, of several transistorsin cascade.

Yours faithfully,G. G. BLAKE,

Department of Chemistry,Sydney University,

Australia.REFERENCES

1. BLAKE, G. G. Improved Apparatus for RectifiedRadio -Frequency Conductimetric Analysis. TheAnalyst 76, (April, 1951).

2. BLAKE, G. G. Conductimetric Analysis atRadio -Frequency. Chapman & Hall, London.

3. BLAKE, G. G. The Development of the Zero -Shunt Circuit. Aust. Journal of Science (April,1944).

4. BLAKE, G. G. New Method for Rapid Measure-ment of Solution Concentration which alsoprovides for the Automatic Control of SolutionStrength. Chemistry and Industry 65, (Jan.1946) and Ref. 2.

A Stable MultivibratorDEAR Sllt,-A multivibrator with a

relay in the anode circuit of one of thevalves constitutes a simple automaticswitching device and often provides asimple means of closing a contact period-ically at a predetermined rate. Such acircuit is, however, sensitive to stray


negative going triggering impulses ortransients occurring when, for example,nearby equipment is switched on and off.The mechanism of triggering followsfrom consideration of the waveform ap-pearing at the grid of each valve (Fig. 1).The multivibrator can change state pre-maturely when either a negative pulse isapplied to the grid of the conductingvalve or a positive pulse is applied to thegrid of the non -conducting valve. The+100

Volts

-100Volts

Valve non-conducting

Valve,conducting

7- 7.....''Fig. 1. Grid waveform of conventional

multivibrator

negative going pulses are generally muchmore objectionable since the valve towhich they are applied will serve as anamplifier, thereby applying a much largerpositive pulse to the other valve.

The effect may be eliminated by usingthe circuit illustrated in Fig. 2, in whichthe capacitors C and C', intercoupling thevalves, have been shunted with 10 meg-ohm resistors 121 and Ri' and series resis-tors R2 and R2' have been included ineach grid circuit. This raises the poten-tials of the points A and A', so that gridcurrent flows during the relevant por-

Fig. 2. A stable multivibrator

tions of the cycle and only a fractionof any small signal picked up on thecircuits connected to these points willbe applied to the grid. In practice thevalues of R,, R2' and 122' are chosen tomaintain A' at a steady state potential ofabout 1 volt when is conducting andV, is cut off.

The resistors R, and RI' do not sub-stantially reduce the period of the multi -vibrator because their values are so highand because they are not returned to theH.T. line but to the anodes of the twovalves, which are at a low potentialduring the relevant portions of the cycle.The circuit modifications described donot, in fact, give rise to any appreciablechange in the anode wave forms. Thepositive going fronts are actually fastersince the loading on the anode resistor -grid coupling capacitor network has beenreduced.

If a relay is included in one anode of

the conventional circuit a damped wavetrain occurs as the valve changes from aconducting to a non -conducting state, andvice versa. These trains are super-imposed on the normal waveform at thegrid of the other valve. While no pre-mature triggering results when the gridis biased beyond cut off it can occurduring the other half of the cycle. Theinterposing of the grid stopping re -

+100Volts Valve n Valve

conducting conduct-ingE - -

-100Volts

Fig. 3. Waveform at A and A' in circuit ofFig. 2

utI volt

sistor R2 will allow the point A to sweeppositive (see Fig. 3) during this period,thus preventing the amplification of theinterfering waveform and subsequenttriggering.

J. H. McGuntE,Boreham Wood, Herts.

Continuous Recording of the Human"Heart -Rate

DEAR SIR,-Would you be good enoughto permit my observations on the articleof Messrs. Boyd and Eadie which ap-peared in the August, 1954, issue.

Under the section " mechanicalmethods," the authors state that theMechano-Electronic transducers employ-ing the mechanically actuated method ofthermionic transference of electricalenergy suffer from the same objections asthe microphone.

This certainly appears to be a correctstatement within the context of the articlebut to people who have not experiencedthe use of the thermionic transducer itwould tend to militate against their con-sideration of the instrument in researchapplications.

The triode thermionic transducer type5734 (produced by RCA in America),presents an overall constant impedance toan amplifier as well as an electrical dis-placement which is linear with respect tothe mechanical forces applied. No micro-phone, or other method of transferringenergy from one source to another, iscapable of meeting the limits of thethermionic transducer, and therefore Ifeel that in fairness to the unit itself,these remarks should be placed onrecord.

Yours very truly,GEORGE LEVINE,

London, E.14.

The authors reply :DEAR SIR, We are indebted to Mr.

Levine for raising this point. Our rejec-tion of any particular method was, ofcourse, not intended in any way to detra7tfrom its value in other applications. Hisviews are fully endorsed on the merits ofthe thermionic transducer when usedunder conditions wherein its uniqu,:features can be adequately employed.

At the same time we are of the opinionthat these valuable features are morewidely known in scientific circles than he

perhaps suggests, and that thermionictransducers would be more freely em-ployed if the present price could bebrought within the financial capacity ofresearch workers.

Yours faithfully,W. E. BOYD, W. R. EADIE,

Boyd Medical Research Trust,Glasgow.

The Design of High Efficiency RadioFrequency E.H.T. Supplies

DEAR SIR,-I was very interested in theRadio Frequency E.H.T. unit described byMr. J. Barron in your September issue,and feel that this has a very wide rangeof potential applications.

In working out the example, however,Mr. Barron appears to ignore the loadingdue to the heater and other auxiliarywindings. In Example 1, for instance, asthe coupling factor is nearly unity, the4V 1A winding will impose a load of

4 x 2 500'- 0.695Mg

6'on the E.H.T. winding. The total load onthis winding is therefore 0.625M12, whichwith a 2 500 turn coil gives a Q of only2, well below the limit specified by Mr.Barron. In this example it would ap-pear more appropriate to use an 800 turncoil, giving a Q of approximately 9.

However, as the author states that hisunit has been in satisfactory operationfor some time, I feel that there must bea fallacy in my argument, and I shouldbe glad to have his views on this point.

J. A. COLLS,Director, Southern Instruments Ltd.,

Camberley.

The author replies :DEAR SIR,-I must thank Mr. Colts for

bringing to my attention the error whichhe mentions. Mr. Coils is quite correctin his statement, and the error is due toconfusion on my part between data fordifferent units. In the example quotedby Mr. Coils, the high voltage coil datawere for a unit giving E.H.T. only, whilethe performance figures are those for theactual unit described. I apologize formy error, and the correct data are asfollows :Example 1

Total effective A.C. load on E.H.T. wind-ing 0.616MU, Q = 8.8, transformer effi-ciency 98.5 per cent. E.H.T. coil 800turns, anode coil 64 turns, grid coil 27turns, rectifier heater coil 3 turns, tubeheater coil 2 turns, remaining data aspublished.Example 2

Total effective A.C. load on E.H.T. wind-ing 0.875M2, Q = 12.4, transformer effi-ciency 98 per cent. Remaining data aspublished.Example 3

Total effective A.C. load on E.H.T. wind-ing 6.51MS2, Q =8.2, transformer effi-ciency 95.4 per cent. Remaining data as,published.

Yours faithfully,J. BARRON,

University of Cambridge,.Department of Physics.


ELECTRONIC EQUIPMENTA description, compiled from information supplied by the manufacturers, of new components,

accessories and test instruments.

Miniature Recorder(Illustrated below)

THIS recorder has been produced tomeet the trend towards miniaturiza-

tion in industrial control equipment. Itmeasures only 4iin by 61 in by 9in deep.

The recorder is of the tapping type,the record being made by an ink -impreg-nated ribbon brought into contact withthe chart by the movement pointer, whichis depressed by the chopper bar opera-ting every 5sec. There are therefore 12taps and consequently 12 recorded pointsmade on the chart every minute (this isat a chart speed of fin per hour). Thechart has straight time lines and hencerectangular co-ordinates. This featureenables the record to be read easily andto be readily integrated if desired.

The recorder is provided with changegears which can be easily selected toprovide chart speeds of fin, lin, 10mm or20mm per hour. The recorder is de-signed to house 33ft of chart, which willprovide for 31 days duration at fin perhour plus 2ft for setting purposes.

The drive for the chart, chopper barand record ribbon is provided by a self-starting synchronous motor.

The recorder movements are of themoving -coil and rectifier -operated mov-ing -coil types, and have a sensitivitydown to lmA for full-scale deflexionwith a resistance of 250 ohms. Thespeed of response is 0.8 seconds for full-scale deflexion. The movement is ade-quately damped.

The maximum self-contained rangesare 500 volts and 10 amperes. The maxi-mum set-up permissible is 4 to 5, e.g.,the chart of a voltmeter may be scaledfrom 200 to 250 volts.

Evershed and Vignoles Ltd,Acton Lane Works,

Chiswick, London, W.4.

Ferrous Metal Standardizer(Illustrated above right)

THE Celsonic standardizer type E.S.2provides a simple and rapid method

of testing small ferrous production sam-ples and components for metallurgicaluniformity as compared with a known

standard sample or component. Theinstrument detects differences in mag-netic permeability between the standardand the sample under test and conse-quently does not damage or mark thetest piece. The degree of departure fromstandard is indicated on a meter. Threedifferent size test heads are normally sup-plied, but special sizes or special shapetest jigs can be supplied to order.

Excel Sound Services Ltd,Celsonic Works,Garfield Avenue,

Bradford, 8.

U.H.F. Transmitting Tetrode(Illustrated below)

THE Communications and IndustrialValve Department of Mullard Ltd

have recently made available a U.H.F.transmitting tetrode, type QV1-150A.This is an external -anode forced -air-cooled ring -seal valve, with an anode dis-sipation of 150W, for use on frequenciesup to 500Mc/s. It is an extremely com-pact valve, with a seated height of lessthan 2in, and has a high power gain atlow anode voltages. The QV1-150Ashould be useful as a U.H.F. power am-plifier, oscillator, or driver, and as ahigh power video amplifier. Thesefeatures make it suitable for use in low -power Band Four television transmitters,and U.H.F. radio links.

The QV1-150A tetrode has an oxide -

coated cathode rated at 6V, 2.6A. Ithas a high mutual conductance (12mA/V)and low interelectrode capacitances. At500Mc/s, it will deliver an output of140W, the D.C. input power being 250W.This valve is equivalent to American type4X150A.

Mullard Ltd,Century House,

Shaftesbury Avenue,London, W.C.2.

Electronic Motor Controller(Illustrated below)

THE outfit comprises a D.C. motor ofabout 1/10th b.h.p. joined by a

flexible cable to the electronic controlunit. The main features are :-

A speed range of 1 000 to 1 in eitherdirection.

The speed is independent of load andsupply changes.

An accurate electrical tachometer isprovided.

The motor armature is supplied witha constant current of 5A D.C. derivedfrom the A.C. mains. The back E.M.F.has virtually no effect on the armaturecurrent, with the result that the maximumrated torque is available over the wholerange of speeds. Mechanically coupledto the motor is a D.C. tachometer gener-ator, which is specially designed to givean output voltage accurately proportionalto speed. The output is metered andforms the basis of the tachometer. Inaddition, the generator voltage is com-pared with an electronically stabilizedreference voltage, and the difference orerror voltage is amplified and applied tothe motor field coils. Thus, if the erroris only 6 rev/min, the motor developsfull torque to accelerate the armature tothe correct speed. The effect is thatover the rated range of torques, thespeed error can never exceed 6 rev/minfor more than a few milliseconds, andit is normally much less than that.

The speed can be smoothly varied overthe range 0 to 6 000 rev/min in eitherdirection, set by fine and coarse controlson the panel.

A high quality electrical tachometer is


provided on tne control panel, with ascale length of 32in and ranges of 100,300, 1 000, 3 000, 10 000 rev/min. Theaccuracy is plus or minus one per cent.

Servomex Controls Ltd,Crowborough Hill,

Jarvis Brook, Sussex.

Anti -vibration Mounts(Illustrated above)

UARRYMOUNTS are now being made1,in this country under licence from theBarry Corporation of America.

The anti -vibration mounts have beenspecially developed for use with airborneequipment of all types, while the shockmounts are primarily intended for use invehicles and ships but under certain cir-cumstances may also be used in aircraft.

The important features of all the anti -vibration mounts are : Use of non-linearsprings to mantain substantially constantnatural frequency over a load range ofapproximately two to one; exceptionallylow natural frequency of 7 to 9c/s; highdegree of damping, eliminating snubbercontact under all normal operating con-ditions and resulting in improved shockabsorption.

Illustrated is a standard air -dampedBarrymount available in ratings from 2to 351b.

Cementation (Muffelite) Ltd,39 Victoria Street,

London, S.W.1.

V.H.F. Anode Connectors(Illustrated above)

THESE anode connectors have beendesigned fot use with valves such as

the Mullard QQV06/40 series. Theyhave good heat dissipation, do not addsignificantly to the output capacitance ofthe valve and can be readily installedand removed in restricted positions.

Power Controls Ltd,Exning Road,

Nevvtnarket.

NOVEMBER 1954

Miniature Relay(Illustrated below)

THE type J.01 relay has a laminatedarmature and frame, a stainless steel

armature shaft, Oilite bearings and buf-fered contacts. It provides heavy con-tact pressure with low coil consumption.Coils can be wound for any voltage upto 100V D.C., and 250V A.C. The maxi-mum number of contacts is eight rated at110V or four rated at 250V. The opera-ting time is within one half -cycle onA.C., and 10 to 20msec on D.C.

Besson and Robinson Ltd,6 Government Buildings

Kidbrook Park Road,London, S.E.3.

Air Blowers(Illustrated above)

THE latest addition to the Plannairrange is the type 2PL81-84 axial flow

blower. It has an overall diameter of3in and a blade tip diameter of 2in. Theair displacement at sea level conditions is35fe/min at 0.4in W.G. It is fullytropicalized and is suitable for groundor airborne duty.

Plannair Ltd,Windfield House,

Epsom Road,Leatherhead, Surrey.

Alternating Current Detector(Illustrated above right)

THE Hivolt A.C. Voltector is an easilyportable instrument which has been

designed to avoid the necessity ofmaking physical contact with a conductorcarrying A.C. power in order to checkwhether it is alive or not. The instru-ment records the presence of the electro-

static field which surrounds a live A.C.conductor, by a deflexion of the meter.It cannot, therefore, be used if the con-ductor is totally enclosed in an earthedsheath. The A.C. voltector will operateon 50V wiring or, at the other extreme,it will indicate from the ground whethera 132kV overhead line is alive or dead.

An A.c. voltector will also indicate theexact position of a break or fault in aline carrying A.C., provided that the lineis not contained in an earthed sheath.

Hivolt Ltd,34a Pottery Lane,

Portland Road,London, W.11.

Junction TransistorHE XFTI is a pnp junction transistor

1 intended for use in hearing aids. Itis hermetically sealed in a flat glass bulbhaving a maximum length of 15mm anda rectangular cross-section of 5.3mm by3.8mm. The germanium junction ele-ment in this transistor is supplied byB.T.H. Ltd. The maximum collector -emitter voltage is -4-5V D.C., and themaximum collector dissipation 6mW. Ina typical amplifier stage a power gain of38db can be realized.

Hivac Ltd,Stonefield Way,

South Ruislip,Middlesex.

U.H.F. Signal Generator(Illustrated below)

THE type L.1 signal generator coversthe frequency range of 300 to 1 000

Mc/s and has a maximum output of notless than 100mV into 752. The outputis measured by means of a crystal volt-meter at the output of the piston attenu-ator, which provides a variation of 126db.

Internal sine and pulse modulation at1 000c/s is provided and provision ismade for external modulation of eithertype. The calibration accuracy is claimedto be within ± 1 per cent.

Advance Components Ltd,Back Road, Shernall Street,

London, E.17.


PHILIPS TECHNICAL LIBRARY

Kretzmann's

IndustrialElectronics

Foreword byProf. JAMES GREIG

M.I.E.E.

230 pages with 250 illustrations 25s.

" The first part describes the general prin-ciples as applied to modern industry. Inpart two a chapter is devoted to each ofthe main types of application; operationof each is described in considerabledetail. Invaluable to technicians who areengaged in supervision or maintenance."-Electrical Journal.

Germanium Diodesby D. S. BOON

A concise well -illustrated book at about8s. 6d., comes in January.

Descriptive Folders fromCLEAVER-HUME PRESS LTD.31 Wright's Lane, W.8

The latest"Electronic Engineering"

monograph

RESISTANCESTRAIN GAUGES

By J. Yarnell, B.Sc., Ainst.P.

Price 12/6 (Postage 6d.)

This book deals in a practical mannerwith the construction and applicationof resistance gauges and with themost commonly used circuits andapparatus. The strain -gauge rosette,which is finding ever wider applica-tion, is treated comprehensively,and is introduced by a short exposi-tion of the theory of stress and strainin a surface.

Order your copy throughyour bookseller or direct from

Electronic Engineering

28 ESSEX STREET, STRANDLONDON, W.C.2

BOOK REVIEWSTelevision Receiver Servicing

By A. E. W. Spreadbury. 310 pp., 187 figs.Demy 8vo. Vol. I. Hiffe & Sons Ltd. 1954.Price 21s.

THIS book, one of two volumes cover-ing the subject, deals with time -bases

and associated circuits and is stated to be" mainly intended for the professionalradio service engineer who, havingalready become skilled in the art of faulttracing in radio receivers, wishes toextend his activities to television servic-ing."

It is a very well produced book, nicelyprinted and illustrated on good paper,and it is disappointing to find the con-tents less useful than a first inspectionwould suggest.

It assumes that the reader is at leastfairly familiar with the theory of tele-vision receivers, the operation of tele-vision time -base circuits, and testequipment including the oscilloscope.

The order in which the material ispresented is mainly logical and practical,and it is clear that the author is familiarwith the problems facing the serviceengineer.

The first chapter deals with many ofthe causes of a blank screen, their loca-tion and elimination. It is obviouslydifficult to clear time -base faults if noraster is visible on the C.R.T. and al-though not really within the scope ofthis book, the faults not connected withtime -bases which cause a blank screen,such as the incorrect adjustment of theion trap, failure of the supplies to theC.R.T. or the tube itself, are discussed.Line flyback E.H.T. systems and theirtroubles are conveniently dealt with inthis chapter and pulse and sine wavevoltage multipliers are illustrated anddiscussed. The author makes the some-what misleading statement that " If theE.H.T. is derived from a flyback systemthis lethal danger . . . (of shocks)ti

. . . is entirely absent, and after verylittle practice a simple trick will revealthe presence of E.H.T. volts. This is tohold a screwdriver, which should prefer-ably have a wooden or insulated handle,close to the anode cap of the tube, whenbright blue sparks should be drawnbetween the two if E.H.T. is present."Preferably insulated! Also " An E.H.T.supply derived from an R.F. oscillator isusually perfectly safe to handle in thesame way as the flyback system andsparks can be drawn from it also." Inthe reviewer's opinion the danger ofshock is treated far too lightly and anyshock may be considerably worse than" unpleasant."

Chapter II follows a logical order anddeals with obtaining a raster. Varioustypes of time -bases and faults whichthey may develop are dealt with in a verypractical way. H.T. boost circuits andtheir possible faults are also discussedbut the subject of H.T. boost is covered

all over again and more fully in ChapterVII.

Chapter III covers the application ofa signal to the C.R.T. which is again alogical step after the production of araster. The chapter includes usefulphotographs of oscilloscope traces. Italso includes sync separators of varioustypes and the effects and location offaults. However, Chapter IV entitled" Synchronization " deals with syncseparators more fully and some materialis repeated. In this chapter the trans-mitted waveform is dealt with, particu-larly the frame pulses, and the effect ofdifferentiator and integrator circuits uponthe shape of the pulses. Interlace filtersand clippers are shown. The number-ing of the lines in the illustrations israther confusing as the top line in theraster is numbered line 1, as is the firstline interval in the complete frame pulse.This might suggest that the frame pulsesoccur during the first few lines of thescan, i.e. at the top of the picture. Fig.58 states incorrectly that the picturemodulation recommences half -way alongline 127.

Interlace quality is considered in Chap-ter V and some of the causes of badinterlace are mentioned. The authormentions the deduction of the " Q " ofthe deflexion circuit from the flybacktraces. This method can easily be shownto be incorrect.

Chapter VI is entitled " The Synchon-ized Time -base " and would have morelogically appeared before the material oninterlace. It is a useful chapter anddeals with many time -base circuits andthe position of their amplitude, hold,and linearity circuits. The televisionservice engineer beginner should findmuch to help him to classify the typesof time -base circuits and variationswhen dealing with a particular circuitfor the first time. Under " single valveline time -bases " two and even threevalve circuits are shown, as well as truesingle valve circuits such as that used sosuccessfully by the Plessey Co. Thiscircuit is at first called " the transitrontype oscillator " and the true reason forconnecting g2 to g3 via a capacitor (forline linearity purpose) is not given. Itis stated, however, that it is " actually aninductive system." It is also stated thatthe C and R in the grid circuit " deter-mine the time -constant." Actually theonly effect of removing the capacitor isa degradation of line linearity.

Chapter VII, as previously mentioned,deals with H.T. boost and does so in acomprehensive way. Like Chapter VI ithas more explanation of the working ofthe circuits than their faults and elimin-ation. There are several parts to puzzlethe reader such as "the voltage of the. . . ." (line) " . . . . output valve anode,however, can always be measured at theopposite end of the mains transformer


winding which is 'earthy,' as can also beanode current."

Chapters VIII and IX cover many ofthe circuits associated with scanning andthe tube itself such as picture shift, spotwobble, and tube protection circuits.The theory and practice of ion trappingis covered very neatly.

Following a useful chapter on flywheelcircuits the book concludes with D.C.restoration and the use of test instru-ments and test card ' C."

In this reviewer's opinion the book fallsbetween the two stools of clear explana-tion of the workings of television cir-cuits, and the purely practical approachto fault-finding. Where explanations aregiven they are not always clear and maynot be very useful to the reader who isseeking help. For example: " Like theblocking oscillator the multivibrator cir-cuit oscillates in sudden spasms ";" Negative charge is built up by framepulses in Ci." Actually Ci is dischargedmore during frame pulses than duringline pulses. Again, when describingsingle diode sync separators " It doesactually employ two valves but thesecond one is a pentode and is onlyborrowed ' to amplify the output in

reflex." The book contains many loosestatements like " . . . line output valvegoes down below chassis . . ."; " . . .

insulation of several thousand volts . . .';66

. curved flyback . . . ." and so on.Where the purely service angle is

attempted a matey style is adopted suchas " until the culprit is found "; " oldfriend the leaky capacitor "; " valve willtry and burn itself up." It gives advicesuch as " a device employed by busyservice engineers is to short-circuit thegrid and cathode pins . . . ." (of theC.R.T.) " . . . momentarily, when ifeverything else is in order the screenwill light up."

Possibly the most odd advice given tothe reader concerns a type of time -basewhich is " lazy." This is " not a fault."The symptoms are a single horizontalline. The customer must be " initiatedinto the simple trick of switching thereceiver on and off quickly." " Provid-ing the trick is known the remedy is atonce obvious," and will save the " un-suspecting service engineer " unnecessarywork.

C. H. BANTHORPE.

Principles of Mass and FlowProduction

By F. G. Woollard. 196 pp.. 102 figs. Demy 8vo.Iliffe & Sons Ltd. 1954. Price 25s.

THE principles and methods des-cribed in this book are suitable for

the manufacture of almost every articlethat is readily and continuously saleable,and production executives in a very widerange of industries, as well as allstudents of engineering economics, willfind the book of interest.

After defining the terms " mass pro-duction " and " flow production " theauthor briefly traces the history of thistype of manufacture. He then laysdown a series of eighteen basic princi-ples that relate to the setting up of flowproduction plant, and considers the im-plication of each in detail.

NOVEMBER 1954

Rutherford, By Those Who KnewHim

69 pp., 20 figs. Dewy 8vo. The Physical Society,London. 1954. Price 5s. (members), 8s. 6d.(non-members).

A FTER the death of Lord Rutherfordin 1937 the Physical Society insti-

tuted a series of lectures in his memory;the Arst of these was given in 1942, andsucceeding ones in 1946, 1949 and 1950.The lectures were published in the Physi-cal Society's Proceedings, and the presentvolume consists of the first five lecturesbound together. They admirably sup-plement the official biography " Ruther-ford " by A. S. Eve, which gives his lifeand work, with copious extracts fromthe correspondence, and N. Feather's" Lord Rutherford," a shorter work,giving a sketch of his life with a criticalsummary of the work and a few extractsfrom correspondence.

The first two lectures, by H. R. Robin-son and Sir John Cockcroft, are remin-iscent and personal, and cover theperiods up to 1919 (New Zealand, Cam-bridge, Montreal and Manchester) andfrom 1919 onwards (Cambridge) respec-tively. Prof. Robinson concentratesmainly on the Manchester period, 1907-19, during a large part of which he wasworking under Rutherford.

The third lecture, by M. L. Oliphant,is entitled " Rutherford and the ModernWorld " and assesses the influence ofRutherford's personality on the progressof atomic physics, on the British scienti-fic effort in World War II and on co-operation within the British Common-wealth.

In the fourth lecture E. Marsden givesa fascinating personal account of theManchester researches, in which he him-self played a notable part, leading to thenuclear theory of the atom, and includesalso an extensive and equally fascinatingstory of Rutherford's upbringing andearly life as a boy and young man inNew Zealand.

A. S. Russell in the fifth lecture againcovers the Manchester period, but fromthe standpoint of a chemist, and quotesmany anecdotes which well bear repeti-tion.

The book contains about 20 illustra-tions: these are mainly from personalsnapshots and are of great interest forthis reason, but lose much through poorreproduction.

From all the lectures appears the samepicture of Rutherford's unique andabounding personality : his forthright-ness, energy and boyish humour, alliedto the keenest scientific insight andpower of penetrating at once to theheart of a problem and solving it. Hehad all the qualities of great leadership,combining outstanding personal achieve-ment with the power of inspiring others,and his death at the comparatively earlyage of 66 was a great loss to Britishscience.

The present volume is a notable com-mentary, worthy of its subject, and maybe confidently recommended to readersin the world of physics and in thoseworlds of engineering which have grownfrom the past century's discoveries inphysics.

F. A. B. WARD.

CHAPMAN & HALL

Ready Shortly

AUTOMATICPROTECTION

OFA.C. CIRCUITS

by

G. W. StubbingsB.SC., F.INST.P., A.M.I.E.E.

Fourth Edition, Revised & Editedby

C. M. Dobson, A.I.E.E.336 pages 213 figures 50s. net

In this edition Mr. Dobson hascompletely revised and re-editedthe chapters dealing with relays andprotective systems and the glossaryof protective engineering terms.He has included an additionalchapter dealing with the earthingof power system neutrals as thissubject is closely associated withthe design and application of mosttypes of protective systems.

37 ESSEX STREET, LONDON, W.C.2

Smith's forTechnicalBooks

Books on the theory and prac-tice of electronics, new devel-opments, circuit design, andother specialized subjects canbe quickly supplied throughyour local Smith's shop orbookstall.

Your copies of ELECTRONICENGINEERING can be boundinto attractive volumes; and all yourstationery and printed matter sup-plied through our local branch.

W. H. Smith& Son

for SPECIALIST BOOKSHEAD OFFICE:

STRAND HOUSE, LONDON, W.C.2


Proceedings of the NationalElectronic Conference 1953

958 pp., 150 figs. Royal ilvo. Vol. 9. NationalElectronics Conference Inc., Chicago. 1954.Price SS.

THIS volume contains the texts of thepapers presented at the 9th National

Electronics Conference held at Chicagoin September 1953. The total numberof papers is ninety-eight and these aredivided into twenty-three sections; eachsection consisting of four or five papers.The coverage includes magnetic ampli-fiers, servo-mechanisms, ultrasonics,television, computors, transistors, micro-waves, nucleonics and communications.It is disappointing to find that there isonly one electro-medical paper and thataudio -frequency work is represented byone paper on a cable -less microphonesystem (using a sub -miniature radio trans-mitter) and two papers on valve micro -phony.

Magnetic amplifiers are discussed infive papers; of particular interest is thepaper from Westinghouse describing atransistor -controlled arrangement. Thecombination of the transistor with a mag-netic amplifier is, of course, particularlyattractive from the reliability point ofview. The section on computors has apaper on a magnetic ring counter. Thisuses a single driving valve per ring witha magnetic core, crystal diode and capa-citor in each stage. The maximumcounting rate is 50kc/s which comparesfavourably with gas -tube ring counters.However, it should be pointed out thatmagnetic counters do not give directvisual read-out, this is a serious disad-vantage in many applications.

The section on circuits has a paper onthe use of the parallel -T network as alinear discriminator for telemetering.Another paper in this section describes anew type of pulse -modulated oscillatorwhich uses a single transmission line todetermine both the pulse duration andthe carrier frequency.

A paper from Bell discusses active -element RC filters. These are inductor -less filters which use a transistor nega-tive -impedance convertor. A furtherfilter paper discusses electro-mechanicalfilters for the frequency range 100kc/sto I Mc/s. Such filters have better selec-tivity characteristics than conventionaldouble -tuned transformers and enable asuperheterodyne receiver to be designedwith virtually all the selectivity in thefirst I.F. stage. This means that thevoltage level due to signals outside thepass -band is reduced at the later stages,with consequent reduction of intermodu-lation and other undesirable effects.

Three papers cover work on theChicago Synchrocyclotron. One of thesepapers describes a high-speed scalerhaving a resolving time of ten milli -microseconds. The scaler uses PhillipsEFP60 secondary emission valves and,due to the method of bias, is not suit-able for continuous operation at highcount rates.

A method of obtaining automatic gaincontrol or transistor amplifiers is des-cribed; a n -p -n junction transistor isused and gain variation is achieved byutilizing the inverse relation betweenemitter resistance and emitter current.Further transistor papers deal withjunction -transistor feedback amplifiers,

with transistor switching circuits andwith an amplitude stabilized transistoroscillator. Although these papers repre-sent original work much of this materialhas now been published elsewhere.

The volume contains review papers onultrasonics, transductor applications andon analog-digital conversion. Owing tothe limitations of the conference time-table these papers are too brief to beof much value. In the case of thereview of transductors only four refer-ences are given, one of which is incor-rect.

The volume is well printed on goodquality paper and, by current standards,it is not unreasonably expensive.

V. H. ATTREE.

Vector and Tensor AnalysisBy G. E. Hay. 193 pp., 66 figs. Doily 8vo.Dover Publications, Inc., New York. 1953.Price $1.50 (paper cover). $2.75 (cloth cover).THE tensor calculus of Ricci and

Levi-Civita came into prominencewith the advent of general relativitytheory in 1916 and has since been suc-cessfully applied to the study of suchsubjects as elasticity, hydrodynamics,and electromagnetic theory. In 1932,Gabriel Kron, an American engineer,introduced tensor analysis to mathemati-cal engineering and succeeded in devel-oping the tensor theory of electricalmachinery. Today, the tensor calculusis almost universally recognized as theproper basis for the unification of elec-trical engineering science. It is appro-priate, therefore, that a purely mathe-matical text -book on tensor analysisshould receive notice in an engineeringperiodical.

This pocket-size book is one of a newscience series recently introduced by thepublishers. Tensor analysis may be des-cribed as a generalized extension of thevector analysis of Gibbs and Heaviside.The latter is confined to Euclidean 3 -space whereas tensor analysis facilitatesthe study of physical phenomena requir-ing generalized co-ordinates in Rieman-nian n -space for their geometrical repre-sentation. Accordingly, the author fol-lows the usual procedure of approachingthe tensor concept by way of vectoranalysis. Five of the six chapters con-tained in the book are devoted to vectors.The first chapter defines a vector and ex-plains the rules of the algebra. Thefollowing two chapters discuss applica-tions to analytical geometry and classicalmechanics while Chapters IV and V dealwith the differential vector calculus andintegration. The final chapter intro-duces tensor analysis and begins withthe inter -reference -frame transformationlaws and thus defines contravariant, co-variant, and mixed tensors. The remain-der of the chapter deals with invariance,the algebra of tensors, and special ten-sors and concludes with applications tomathematical physics. Unfortunately,as is usual in mathematical text -books,no examples are given of Kron's applica-tion of tensors to electric circuit theory.

Although the final chanter of the bookmight be used to provide the mathe-matical background for an introductionto Kron's work, it is difficult to see whatit has to offer to readers in this countrythat is not already well represented by

such books as those of Rutherford andSpain in the Oliver and Boyd series. Thebook is available in cloth or paper bind-ing but bears evidence of hurried pre-paration. Misprints such as covaritanand invarinat have escaped notice. Dueto a printing blunder, several diagramshave been reproduced to the wrong scalenecessitating the insertion of a loose sup-plement showing larger reproductions.The book has no introduction, no index,and gives no answers to the problems setin each chapter.

S. R. DEARDS.

Fluorescence Analysis in Ultra -Violet Light

By J. A. Radley and Julius Grant. 560 pp., 64figs. Medium 8vo. 4th Editiom. Chapman& Hall Ltd. 1954. Price 52s. 6d.

THEprevious edition of this book was

published as long ago as 1939 and theinterval which has elapsed is due largelyto circumstances arising directly out ofthe war. In addition, republication hasbeen deliberately deferred because it wasfelt that it was desirable to wait untilthe work published during the warperiod, particularly in what were enemycountries, could receive the fullest con-sideration. Attention may be drawn inparticular to the entirely new sectiondealing exclusively with the applicationsof fluorescence analysis to the evaluationof vitamin activity. New lamps for theproduction of ultra -violet light, and newapparatus and technique used for fluor-escence analysis are also dealt with.

Laplace Transforms for ElectricalEngineers

By B. J. Starkey. 280 pp., 60 figs. Demy 8vo.IGQe & Sons Ltd. 1954. Price 30s.IN this book a physical rather than aI purely mathematical vocabulary isused in an attempt to attain the utmostsimplicity, and throughout the approachis from analytical methods already wellknown to the reader. The work is notintended as more than a general intro-duction to a very large subject, but it ishoped that it will be of value in supple-menting the more rigorously mathemati-cal texts that have previously appeared.

The author, who is on the staff of theRoyal Aircraft Establishment at Farn-borough, has lectured electrical engineerson the subject.

The Oscilloscope at WorkBy A. Haas and R. W. Hallows. 172 pp., 102fies. Demy 8vo. Iliffe & Sons Ltd. 1954. Price15s.

A LTHOUGH, as the title implies, this11. book deals mainly with the uses ofthe instrument and correct interpreta-tion of the oscillograms produced, it alsocontains valuable information on oscillo-scope circuits, construction and adjust-ment, while one chapter is devoted toexplaining how it can be made to diag-nose its own troubles when faultsdevelop.

This work was originally published inFrance and has now been adapted forEnglish speaking readers and consider-ably enlarged.


Short News Items

The Scientific Instrument Manufacturers'Association announce an exhibition ofelectronic aids to production, design andresearch, under the title, " Electronics atWork," to be held at the Chamber ofCommerce Hall, Birmingham, from 23-25November. Admission is by ticket,obtainable free on request from theAssociation at 20 Queen Anne Street,London, W.1.

A new private automatic branch telephoneexchange has recently been installed in theheadquarters of BOAC at London Airport.The exchange was built by the AutomaticTelephone and Electric Co Ltd and has1 300 extensions, 95 exchange lines and 60private wires. Direct dialling betweenextensions is provided. An importantfeature is a " hold for enquiry " facilitywhich enables users to hold an incomingexchange call and to make, at the sametime and on the same telephone, a furthercall to either an external or internal line ;the original call can be restored by merelypressing a button. An operator recallbutton has also been fitted. Outgoing callsup to a value of sixpence can be dialled fromany extension, above this amount they arereferred to the operator.

Metropolitan -Vickers Electrical Co Ltdannounce that the Chairman, Sir George E.Bailey,' and the Deputy Chairman, SirFelix J. C. Pole, have resigned from theBoard of Directors. The Rt. Hon. TheViscount Chandos (formerly Mr. OliverLyttelton), has been elected a Director andChairman of the Board.

The United Kingdom Atomic EnergyAuthority has opened a Reactor School atHarwell as a step towards encouragingindustry to play a greater part in thedevelopment of atomic power. The newschool will provide, for a fee of £250, athree months' course of training for stafffrom industrial concerns to learn thetechniques by which heat from atomicpiles can be converted into useful power.Three courses will be held each year,starting in January, May and September.Applications for places in the school shouldbe made to the Manager, Reactor SchooA.E.R.E. Harwell, Berkshire, and showgive sufficient information for the Manament Board to assess whether the stud nthas the required academic standard orentry to the school.

The Eastern Joint Computor Conferenceand Exhibition will be held at the BellevueStratford Hotel, Philadelphia, from 8-10December. The programme includes paperson computor comparisons, input-outputdevices, computor systems and character-istics, mathematics, and business andscientific applications. Some sixtycompanies will be taking part in theexhibition.

The Golden Jubilee of the InternationalElectrotechnical Commission was celebratedin Philadelphia in conjunction with a seriesof technical meetings which took placefrom 1-16 September. The number ofdelegates attending was among the largestin the history of the IEC. The majoritycame from the United States. The secondlargest delegation was that from the UnitedKingdom, followed by France, Germany,Italy, Sweden, Netherlands and Switzer-land. Altogether twenty of the thirtymember countries of the IEC were repre-sented. Lord Waverley, Chairman of thePort of London Authority and immediatePast President of the British StandardsInstitution, led the comprehensive Britishdelegation.

Marconi's Wireless Telegraph Co Ltdannounce the placing of recent orders foraeronautical radio equipment from theU.S.A., India, South Africa and France.More than forty airlines and over twentyAir Forces now use Marconi aeronauticalequipment. The first three of the Vickers -Armstrong Viscounts ordered by CapitalAirlines (U.S.A.) will each have a dualinstallation of the new Marconi AD7092C automatic direction finder (radiocompass). The two Viscounts ordered bythe Indian Government are to carryMarconi communications and automaticdirection -finding equipments. Marconiradio equipment will also be installed ineach of the Avro Shackleton Mark IIIaircraft now on order by the South AfricanAir Force. France is also to have theAD 7092D radio compass in each of theEnglish Electric Canberras on currentdelivery.

The Eighth Annual Amateur RadioExhibition organized by the Radio Societyof Great Britain will be held as in formeryears at the Royal Hotel, Woburn Place,London, W.C.1, from 24-27 November.The Exhibition will be open at 11 a.m. andclose at 9 p.m. each day, admission 1 s.

edifon Ltd announce that a substantiaorder for radio equipment has been placedwith them on behalf of the Soviet FishingAuthority. The equipment, comprisingtransmitters, all -wave receivers, combinedmedium and short-wave direction findersand associated ancillary units, will beinstalled in the twenty deep-sea fishingvessels now under construction for theSoviet Union by Brooke Marine Ltd ofLowestoft.

Mr. T. R. Thomson, Assistant Comp-troller to J. Lyons & Co Ltd, has plannedto give the following talks on LEO, LyonsElectronic Office, and associated matters.On 8 November, to the Insurance Instituteof London, " The Practical Use of theElectronic Computor." On 18 November,

to students of the North West Polytechnic," High Speed Automatic ElectronicComputing Designed for Office Work."

The BBC announces that the new tele-vision station at Rowbridge in the Isle ofWight will be brought into full programmeservice on 12 November. The new stationwill use initially a temporary mast andaerial system and is expected to providesatisfactory reception in the Brighton area,along the south coast to Bridport, andinland as far as Devizes and Newbury.When the permanent 500 -ft. mast andaerial system are completed in about ayear's time, the service will be extended tocover Seaford in the east, Seaton in thewest, and Lambourn in the north.

Microwave Instruments Ltd have recentlycompleted extensions to their factory atWest Chirton Industrial Estate, NorthShields. It is their intention to make themajority of this additional working spaceavailable to accept specialist sub -contractwork.

20th Century Electronics announce theopening of an extension to their newfactory at New Addington, Surrey. Thisextension doubles the size of thebuilding. The factory and researchlaboratories of the Cathode Ray Tubesection, formerly at Dunbar Street, London,S.E.27, have now moved to New Addington.

Claude Lyons Ltd of Liverpool andLondon have acquired a new factory knownas Valley Works, 4-10 Ware Road,Hoddesdon, Herts. In addition to housingresearch and development staff, the newpremises will be employed for a smallamount of new product manufacture, andalso in increasing stock facilities.

W. Canning & Co Ltd of Birminghamannounce the introduction of a new type ofchrome plating anode. It has beendeveloped from the older type of copper -cored anode, but now utilizes aluminiumor its core.

rrata. The following alterations shouldbe made to the article by Mr. R. Voleswhich appeared on pp. 452-453 of theOctober issue.

The lower limit of all the summationsigns in equation (2) should be p = 1.

The term giving the position of thecentre in section (c) of the paragraphheaded " T Loci " should be ((1 -T, 0).

The first inequality in the exampleanalysis should have a summation signwith a lower limit of p = q.

The extreme terms in the inequality (3)should be preceded by minus signs.


Meetings this MonthTHE BRITISH INSTITUTION OF

RADIO ENGINEERSDate: 24 November. Time: 6.30 p.m.Held at: The London School of Hygiene and

Tropical Medicine, Keppel Street, Gower Street,London, W.C.1.

Lecture: The Development and Design of Direct -Coupled Oscilloscopes for Industry and Re-search.

By: M. J. Goddard.Scottish Section

Date: 14 November. Time: 7 p.m.Held at: The Institution of Engineers and Ship-

builders, Elmbank Crescent, Glasgow.Lecture: The Latest Developments in Television

Cameras.By: H. McGhee.Date: 11 November. Time: 7 p.m.Held at: The Department of Natural Philosophy,

The University, Edinburgh.Lecture: Nuclear Fission and Nuclear Fusion.By: N. Feather.

Merseyside SectionDate: 4 November. Time: 7 p.m.Held at: The College of Technology, Byron

Street, Liverpool, 3.Lecture: Radio Receiving Valve Manufacture.By: G. P. Thwaites.

North-Western SectionDate: 4 November. Time: 7 p.m.Held at: Reynolds Hall, College of Technology,

Sackville Street, Manchester.Lecture: Electronic Servo Mechanisms.By: J. L. Russell.

North-Eastern SectionDate: 10 November. Time: 7 p.m.Held at: Neville Hall, Westgate Road, Newcastle-

upon-Tyne.Lecture: Stereophonic Sound.By: R. A. Bull.

South Wales SectionDate: 17 November. Time: 6.30 p.m.Held at: Cardiff College of Technology, Cathays

Park, Cardiff.Lecture: The Techniques of Power Measurements

from D.0 to 5Mc/s.By: G. F. Lawrence.

THE INSTITUTE OF PHYSICSDate: 9 November. Time: 6.30 p.m.Held at: The Institute's House, 47 Belgrave

Square, London, S.W.1.Lecture: The Materials of Atomic Energy.By: H. M. Finniston.

Manchester and District BranchDate: 12 November. Time: 6.45 p.m.Held at: The Bragg Lecture Theatre, University

of Manchester.Lecture: Colour Measurement as a Tool inScientific Research.By: W. D .Wright.

THE INSTITUTION OFELECTRICAL ENGINEERS

All London meetings, unless otherwise stated,will be held at The Institution, commencing at

5.30 p.m.Ordinary Meeting

Date: 4 November.Lecture: A Transatlantic Telephone Cable.By: M. J. Kelly, Sir Gordon Radley, G. W.

Gilman and R. J. Halsey.Education Discussion Circle

Date: 8 November.Discussion: Methods of Teaching Technical

Writing.Opened by: G. Parr.

Radio and Measurements SectionsDate: 10 November.Lectures: Standard Frequency Transmissions.By: L. Essen.The Standard Frequency Monitor at the National

Physical Laboratory.By: J. McA. Steele.Standard Frequency Transmission Equipment at

Rugby Radio Station.By: H. B. Law.

Informal MeetingDate: 15 November.Discussion: Has Nuclear Fission a Future as a

Source of Industrial Power ?Opened by: Sir Harold Roxbee Cox.

Celebration of the Jubilee of the ThermionicValve

Date: 16 November. Time: 2.30 p.m.Opening Address by The Most Honourable the

Marquess of Salisbury, Lord President of theCouncil, followed by lecture: The Genesis ofthe Thermionic Valve.

By: Professor G. W. 0. Howe.Time: 3.30 p.m.

Lecture: Thermionic Devices from the Develop-ment of the Triode up to 1939.

By: Sir Edward Appleton.Time: 5.30 p.m.

Lecture: Developments in Thermionic Devicessince 1939.

By: J. Thomson.Measurements Section

Date: 30 November.Discussion: The Servicing of Electronic Measuring

Instruments and its Effect on their Design.Opened by: Denis Taylor.

East Midland CentreDate: 23 November. Time: 6.30 p.m.Held at: The Gas Department, Demonstration

Theatre, Nottingham.Lecture: Telemetering for System Operation.By: R. H. Dunn and C. H. Chambers.Date: 26 November. Time: 6.30 p.m.Held at: The College of Technology. Leicester.Lecture: A Radio Position Fixing System for

Ships and Aircraft.By: C. Powell.

Cambridge Radio GroupDate: 8 November. Time: 8.15 p.m.Held at: The Cavendish Laboratory, Free School

Lane, Cambridge.Radio Section Chairman's Address.

Mersey and North Wales CentreDee: 29 November. Time: 6.30 p.m.Held at: The Liverpool Royal Institution, Colquitt

Street, Liverpool.Lecture: A Short Modern Review of Fundamental

Electromagnetic Theory.By: P. Hammond.North-Eastern Radio and Measurements GroupDate: 15 November. Time: 6.15 p.m.Held at: King's College, Newcastle-upon-Tyne.Lecture: A.C. Instrument Testing Equipment.By: A. H. M. Arnold.

North Midland CentreDate: 2 November. Time: 6.30 p.m.Held at: The offices of the British Electricity

Authority, Yorkshire Division, 1 WhitehallRoad, Leeds.

Lecture: Technical Arrangements for the Soundand Television Broadcasts of the CoronationCeremonies on 2 June, 1953.

By: W. S. Proctor, M. J. L. Pulling and F.Williams.

THE INSTITUTION OF POSTOFFICE ELECTRICAL ENGINEERS

Ordinary MeetingDate: 9 November. Time: 5 p.m.Held at: The Institution of Electrical Engineers,

Savoy Place, London, W.C.2.Lecture: Future Demands for Telephone Service-

possible trends and reactions.By: J. M. Norman.

Informal MeetingDate: 24 November. Time: 5 p.m.He'd at: The Conference Room, 4th Floor,

Waterloo Bridge House, London, S.E.1.Lecture: Some Personal Views on the Mechaniza-

tion of Auto Exchange Maintenance.By: F. H. Horner and B. H. E. Rogers.

THE TELEVISION SOCIETYDate: 12 November. Time: 7 p.m.Held at: 164 Shaftesbury Avenue, London, W.C.2.Lecture: Faulty Interlacing.By: G. N. Patchett.Date: 18 November. Time: 7 p.m.Conversazione at University College, London, to

mark the Jubilee of the Invention of theThermionic Valve.

Date: 25 November. Time: 7 p.m.Held at: 164 Shaftesbury Avenue, London, W.C.2.Lecture: European Television Programme Ex-

changes.By: N. J. L. Pulling.

PUBLICATIONSRECEIVED

THE APPLICATION OF PLASTICS IN THECABLE INDUSTRY is an interesting booklet onthe subject produced by the Telegraph Construc-tion and Maintenance Co. Ltd., Telcon Works,Greenwich, London, S.E.10.

COLLOIDAL GRAPHITE FOR METAL-WORKING OPERATIONS is the title of anillustrated brochure published by Acheson ColloidsLtd., 18 Pall Mall, London, S.W.1.

TCC CONDENSERS describes the many typesof condensers produced by the Telegraph Con-denser Company. This catalogue describes thetypes of condensers under the headings ofPaper, Electrolytic, Mica, Ceramic, Plastic Filmand Special Purpose, a different colour beingused for each section. The Telegraph CondenserCo. Ltd. (Radio Division), North Acton, London,W.3.

PHILIPS SERVING SCIENCE AND INDUSTRYis the title of a new monthly publication. Itwill be devoted to new types of mdustrial equip-ment and industrial processes covering a widefield. The publication is distributed free ofcharge and though a substantial mailing list hasalready been built up, a limited number of appli-cants may still be accepted. Requests should bemade to the Publication Department, PhilipsElectrical Ltd., Century House, ShaftesburyAvenue, London, W.C.2.

THE COUNCIL OF INDUSTRIAL DESIGN9th ANNUAL REPORT covers the period 1

April, 1953 to 31 March, 1954, and suggests that,to supplement well established exports of tradi-tional designs, British industry must study modernminded industry abroad. The Council of Indus-trial Design, Tilbury House, Petty France,London, S.W.1. Price Is. 6d.

ENTHOVEN SOLDER PRODUCTS is a leafletwhich is available free on application toEnthoven Solders Ltd., 89 Upper Thames Street,London, E.C.4.

HILGER COMPACT 3 METRE GRATINGSPECTROGRAPH is a booklet describing thisinstrument which is specially designed for indus-trial and research work. HILGER MICRO -FOCUS X-RAY UNIT, incorporating theEhrenberg and Spear tube is a leaflet describingthe main features of this unit. Both publicationsare available from Hilger and Watts Ltd., HilgerDivision, 98 St. Pancras Way, Camden Road,London, N.W.1.

BULLETIN OF SPECIAL COURSES INHIGHER TECHNOLOGY 1954-55 is a bookletissued by London and Home Counties RegionalAdvisory Council for Higher Technological Edu-cation. The purpose of the bulletin is to givepublicity to special advanced courses held in theLondon and home counties region which do notregularly appear in college calendars or prospec-tuses as part of a grouped course or as subjectsoffered for endorsement on Higher National Cer-tificates. Copies may be obtained from TheSecretary, Regional Advisory Council, TavistockHouse South, Tavistock Square, London, W.C.1.

RADIO, TELEVISION AND RADAR is an ex-cellently compiled list of books held in theNottingham Public Libraries. All the items listedare held in either the Central Lending Library orin the Reference Library. Notes on using the ser-vices provided by the Public Libraries are givenat the end of the list. Central Library, SherwoodStreet, Nottingham.

CABINET SYSTEM AND TELESCOPICMOUNTINGS is a catalogue which comprehen-sively describes the Widney-Dorlec CabinetSystem, and embodies all the improvements andadditions that have been made. Hallam, Sleigh& Cheston Ltd., Widney Works, Birmingham, 4.

INSULATING AND PROTECTIVE TAPES is abrochure which includes the tapes in most com-mon use for solid type paper insulated cables upto 33kV and for vulcanized rubber insulatedcables. Copies are available, free of charge,from British Insulated Callender's Cables Ltd.,21 Bloomsbury Street, London, W.C.1.


Date post:	22-Mar-2021
Category:	Documents
Upload:	others
View:	1 times
Download:	0 times

LABORATORY. ELECTRONIC ENGINEERING · 2020. 11. 1. · John Ambrose Fleming was born on 29...

Documents