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-- ill liili 111111lassasemsssm 1 § illiilil m s I 5-^vicbg ill! I • ~,f;S-sR litisic ! ' :| .:. rmsistor ■ 1 ;. \.: Mb. | r't mSm■■ | Radios and w&gm■■ 1 i Printed m •Hi' wmSm l s n % s■' trcuits m B warn■mmm ■t 9BH it t I : t H LAME mm■ -: I: 0p| s. III vv ■Sh BS .-.■t ■mm r, m mm Servicing Transistor Radios and Printed Circuits LEONARD LANE Edited for this edition by E. A. W. SPREADBURY, m.brit.i.rjs. Technical Editor, Wireless and Electrical Trader BIBLIOTHEEK 8 107604" T.H.EINDHOVEN LONDON ILIFFE BOOKS LTD i i . Published in Great Britain, 1062, by Iliffe Books Ltd., Dorset House Stamford Street, London, S.E.I Revised material for this edition © Iliffe Books Ltd., 1962 Published in the U.S.A. under the title . How to Fix Transistor Radios and Printed Circuits by Watervicw Publishing Co. and Gcmsback Library, Inc ' © 1959. ipdl.^Radio-Tclcvision^'raming ! I ! 1 r ; Printed and bound in England by The Chapel River Press Ltd Andover, Hants ; i BKS 4187 ) v ! • < .a■ Contents Preface 7 Introduction 9 1 Semiconductor Fundamentals i 2 How Transistors Work 18 3 Basic Amplifiers 40 4 R.F. and I.F. Stages 6o 5 Detectors and A.G.C. 84 6 Audio Amplifiers ioi 7 Servicing Methods—Part I 125 8 Servicing Methods—Part II 146 9 Car Radio 171 10 Alignment and Measurements 195 11 Printed Circuits 218 12 Transistor Types 235 Appendix Servicing Guide 246 Index 257 5 ' ; ; l . i f . ; 3 Preface This book, a revised version of a Transistor Radio Repair Course offered by a leading manufacturer in co-operation with Radio Television Training of America, aims to give the service technician a better-than-average working knowledge of transistors, their components and associated circuitry. Semi­ conductor materials are the foundations from which the building blocks of basic transistor circuitry are developed. Stage by stage the electronic struc­ ture of the complete transistor receiver is assembled and analysed. Mathematics has been avoided for easier reading. But this does not mean that any technician can entirely ignore such basic calculations as Ohm’s law constantly forced upon him in his daily work. The new concepts of semiconductor applications in the entertainment field have not been oversimplified, but the text does try to allay any fears of delving into a strange new world of low voltages and high capacitances not encountered in the more familiar valve circuits. The text is written in a friendly manner to help the technician feel at home in this wonderland of semiconductors that promise to increase the electronics field tenfold. Not only has the portable radio given new life to the broad­ cast entertainment field, but already pocket-size transistor-operated two- way communicators are available to save steps and time. This book teaches you their principles; they are a stepping stone to the myriad uses of semi­ conductors in commerce and industry. Sooner than you might expect, the production techniques used by manu­ facturers to bring music and news to you anywhere at the turn of a knob will also allow you to keep in touch with, not only business associates, but your family and friends as well. Microscopic in comparison with today’s computers, handy calculators will replace the engineer’s slide rule and even the accountant’s adding machines and more complex calculators. Movies will be recorded, with sound, on magnetic film and viewed through television sets, without any additional processing. These and many more marvels will be produced using the same basic theories that made possible the transistor portable radio. The material learned here will, when properly applied, be an additional source of revenue for the practising electronic technician. Time saved by improved techniques means more jobs can be handled in a normal workday, and work that previously had to be passed on to others can now be handled— and both mean added income. 7 PREFACE In any course of study, review of the basic points is a constant necessity; therefore, none of the repetitions have been deleted. Some facts and tech­ niques are common to many circuits and may be included in the text at all of these points as reminders as well.as reviews. Some techniques are injected into the theory where appropriate, and again presented to emphasize a practical application of a principle in servicing in the second part. In the second half of the book, the emphasis is on the practical applications of the semiconductor fundamentals presented in the first half. General servicing methods are stressed. For example, the special techniques required to test batteries and how to determine the circuit defects that cause seemingly short battery life are described. We will show why, although percentage-wise the tolerances of semiconductor circuits are equal to valve parameters, small voltage changes are just as troublesome in these low- impedance circuits as the more apparent changes caused by defective valve components. Special consideration is given the unique problems of hybrid and all- transistor car radios. Here some types of interference are treated as part of radio servicing although it is actually a characteristic fault of the internal combustion engine used to propel the radio and its listener through the most difficult conditions possible for reception of radio waves. Circuit alignment and measurements are spotlighted. Ways of using the commonly available test equipment for in-circuit component and transistor evaluation is covered and common valve servicing techniques adapted to the low-impedance and low-voltage characteristics of transistor circuitry. Printed-circuit boards are evaluated, and their advantages and disadvantages analysed from a servicing viewpoint. Some simple practical repairs are described. This volume also covers the many types of transistors created by different manufacturing processes. Some basic circuits are used to illustrate the applications for which these specialized semiconductors were designed. The engine of the horseless carriage of yesteryear bears as little resemblance to the power-plant of modem-day earthmovers as the transistor of today and the marvels it makes possible will resemble the as yet undreamed-of possibilities of future semiconductor devices. Just as Fleming’s valve generated a multi-billion dollar industry, semi­ conductor operated devices are sparking a new spiral of development whose future wonders we can only guess at. But one thing is certain: ever-increasing numbers of knowledgeable technicians will be needed. And don’t forget that all big circuits are made up of little circuits, that the sophisticated circuitry of complex machinery utilizes the same basic theories that we are studying. May this book be a stepping-stone to a better and more prosperous future for everyone. Leonard Lane 8 Introduction In anglicizing this book from the American edition I have tried to retain the author’s original style as far as possible, but the differences between the American idiom in which it is written and general English usage in the United Kingdom have resulted in modifications to the text. As far as possible the author’s free and easy style have been retained, and even in many cases a looseness of phrasing to which a scientifically minded purist might take exception. But this book is not addressed to the purists. It is written for the novice, be he an apprentice service engineer, a keen amateur or even a young boy, anxious to learn somcdiing about those remarkable litde sets that work off a torch battery. In this respect the author succeeds admirably. He is obviously a practical man himself, and he talks and writes in a practical manner that the novice can easily take in. Often he uses the novices own language, and if the purist questions the wisdom of this, let him try to explain the working of a transistor to a novice. This little book is an easy-to-read explanation of the subject, embracing all its aspects from the domestic receiver angle, including printed circuits, and I confidendy recommend it to the type of enthusiast for whom it was written. E. A. W. Spreadbury 9 - *. ■ CHAPTER I Semiconductor Fundamentals The transistor is a comparatively new device (it was invented in 1948 and developed since that time), yet its ancestry is older than that of the valve. Radio receivers and radio broadcasting became popular soon after the end of the first World War. In those days, valves were so new and expensive that the crystal detector persisted alone. This crystal detector (Fig. 1.1) was made of a variety of materials such as iron pyrites, galena or carborundum. These minerals, for that is what they are, were used as detectors or signal rectifiers. They formed the heart of the crystal set, a very popular receiver noted for the fact that it required no outside power source, did not need an on/off switch and could be left on indefinitely. The receiver had the advantage of being foolproof and shockproof and could be constructed by practically anyone. At the height of its popularity the crystal set was probably as widely used as television receivers are today. It had, however, a very serious disadvantage. The crystal detector could rectify the signal but could not amplify it; and so, hand in hand with the crystal set, came a pair of headphones. Headphone reception, though, is a very tiresome affair, and it was not long before the crystal set was superseded by the valve receiver—despite the fact that valves were expensive. For a number of years the crystal set and its crystal detector were banished to the attic. With the growth of the television industry, however, the crystal, now completely enclosed and with a fixed contact in place of the “ cat’s whisker ”, was put back into service, but it still performed its old function—that of a detector (Fig.

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