Electronic Components Tubes and Transistors BY G. W. A. DUMMER M.B.E., M.I.E.E., SEN. MEM. I.E.E., M.I.E.R.E. PERGAMON PRESS OXFORD LONDON EDINBURGH · NEW YORK PARIS · FRANKFURT Pergamon Press Ltd., Headington Hill Hall, Oxford 4 & 5 Fitzroy Square, London W.l Pergamon Press (Scotland) Ltd., 2 & 3 Teviot Place, Edinburgh 1 Pergamon Press Inc., 122 East 55th Street, New York 22, N.Y. Pergamon Press GmbH, Kaiserstrasse 75, Frankfurt-am-Main Federal Publications Ltd., Times House, River Valley Rd., Singapore Samcax Book Services Ltd., Queensway, P.O. Box 2720, Nairobi, Kenya Copyright © 1965 Pergamon Press Ltd. Library of Congress Catalog Card No. 65-19841 First edition 1965 Set in Times 10 on 12 pt and Printed in Great Britain by Blackie and Son Ltd., Glasgow This book is sold subject to the condition that it shall not, by way of trade, be lent, resold, hired out, or otherwise disposed of without the publisher's consent, in any form of binding or cover other than that in which it is published. Preface COMPONENT parts are the building blocks of all electronic equip ments. This book is intended to bridge the gap between basic measurement theory of resistance, capacitance and inductance and the practical application of electronic components in equip ments. Basic theory of electron tubes and semiconductors is available in other textbooks and the more practical, or usage, aspect is dealt with in this volume. Experience in the correct choice of a component, tube or transistor is difficult to achieve and incorrect use of these devices may result in expensive repairs. The reliability of complex electronic equipments depends a great deal on the choice and correct use of the individual component parts. The essential characteristics of each main type of component, tube and tran sistor are therefore summarized and references given for further reading if desired. It is hoped that this book will help the student over the difficult problem of choosing the right component and device for his particular application. G. W. A. DUMMER Acknowledgements THE author would like to acknowledge the help and valuable comments of Mr. C. H. Miller, Dr. J. W. Granville, Mr. M. W. Foulkes-Roberts, Mr. W. T. Blackband, Mr. D. E. H. Jones and Mr. P. Lloyd in the preparation of this book. The valuable advice of Mr. W. Hickson of the College of Electronics, Malvern, on the requirements of modern students and particularly in the preparation of the questions, is specially acknowledged. The author would also acknowledge the co-operation of Messrs. Sir Isaac Pitman & Sons in allowing certain material from the "Radio and Electronic Components" series on com ponents to be summarized in this book. Acknowledgement is also made to Messrs. Standard Telephones and Cables Ltd. for permission to use data from their Components News, also the Mullard Co. and all other firms who have provided drawings of components. The views expressed in this book are those of the author and do not necessarily represent the views of the Ministry of Aviation. CHAPTER ONE Fixed and Variable Resistors Fixed Resistors Resistors are generally available in one of two categories—high- stability or general-purpose. High-stability types include the pyrolytic or cracked-carbon resistors, the wirewound resistors and the metal or metal-oxide film resistors, all of which are capable of providing stable resistance to within 1 or 2 per cent. General-purpose types are usually of carbon composition and are cheaper and usually smaller. There are two methods of manu facture of carbon composition resistors—the solid rod con struction shown in Fig. 1.1 and the film construction shown in Fig. 1.2. They are not so stable, and resistance variations on load may be from 5 to 20 per cent. The characteristics of the individual types of resistor vary widely, and it is necessary to know these variations before a choice can be made of the correct resistor for any particular application. The essential characteristics are summarized in terms of the parameters usually required in choosing a resistor. Size In general, carbon resistors dissipate less power than wire- wound resistors of the same resistance value, and are smaller. The maximum resistance of a wirewound resistor is limited by the length of wire of a given material and diameter which can be wound upon the available former length. Subminiature cracked- 2 ELECTRONIC COMPONENTS, TUBES AND TRANSISTORS Sprayed Metal Solder Paint Coating Contact JL Resistive Carbon Composition End m Connection > Uninsulated types Resistive Carbon Composition r Paint Coating " ' Embedded Connection ΖΖΣΖΖΞ) Moulded Resistive Carbon Thermosetting Composition Plastic Cover End Cap. Insulated types End Sealing, (Force fit Cement ' on Rod) Tube Resistive Carbon Γ Composition Rod Ends of Rod Metal-sprayed FIG. 1.1. Carbon composition {solid rod) types. carbon high-stability resistors are made which are comparable in size with the carbon composition type, which may be as small as TO m· diameter and \ in. long. Metal and oxide film resistors are usually larger for high resistance values because of their lower (ohms/square) resistivity. Glass Tube F*P lastic Moulding n End v S N \ N \fN N Connection j Conducting Resistive. Cement Coating _Wire Termination Inserted "Inside Tube to Conduct Away Heat FIG. 1.2. Carbon composition film type. FIXED AND VARIABLE RESISTORS 3 Power-handling Capacity Composition resistors are commonly available for dissipating up to about 2 W, but rarely over 5 W (except in special resistors of low ohmic values). Cracked-carbon resistors (see Fig. 1.3 for Silicon Cracked-carbon Lacquer Film Coating Spiralled Colloidal Ceramic Track Graphite Rod FIG. 1.3. Cracked-carbon film {pyrolytic) type. construction) are available up to 2 W at normal temperatures. All these ratings have to be reduced when the resistors are used at high ambient temperatures. Small metal film resistors (see Fig. 1.4) are made up to 2 W dissipation and small oxide film FIG. 1.4. Metal film {nickel-chromium) types. resistors up to 6 W dissipation. Wirewound resistors (see Fig. 1.5) are invariably used when higher powers are to be dissipated, and some vitreous-enamelled wirewound types will handle powers as great as 300-400 W (see Fig. 1.6). Large oxide and metal film resistors are made also to dissipate several hundred watts. It is important to remember that the temperatures reached by the 4 ELECTRONIC COMPONENTS, TUBES AND TRANSISTORS Wire-wound Moulded resistance element Resin Leads crimped to element FIG. 1.5. Wirewound general-purpose (moulded) type. Nicke/- Chrome Wire Tinned Copper Welded to Resistance Wire Soldered Wire and Brazed to to End Cap End Cap Nickel-Chromium or Nickel-Copper End Cap 3. mmr—R$esi stance Winding Ceramic Vitreous Tube Former Enamel Coating Brazed Connection to Nickel- Chrome Anchor Winding Ceramic -Resistance Vitreous Tube Wire Enamel Coating Wire Winding Ceramic Alternative Tube 0 Ending Q End , Connection FIG. 1.6. Wirewound general-purpose (vitreous-enamelled) types. FIXED AND VARIABLE RESISTORS 5 resistors when dissipating these wattages can be very high—of the order of several hundred degrees Centigrade. There is a "critical value" of resistors for each wattage rating, v2 given by R =— , at which the maximum voltage is applied for the w given wattage. In pulse operation (particularly when the duty cycle is low) only the mean power is effective in raising the internal temperature of a resistor. As the power is supplied in short pulses, very high peak ratings are possible, but the mean power should not exceed the continuous rating wattage. Peak pulse voltages for high-stability (cracked-carbon) resistors should be limited to twice the normal rated d.c. voltage, otherwise the limit set by internal sparking or external corona might be exceeded, while for general-purpose carbon composition resistors, the maximum peak pulse voltage should be no greater than the maximum continuous rating. Stability Stability and accuracy are often confused. Stability is the change in resistance under shelf life or working conditions; accuracy is the tolerance to which the value of the resistor is made or selected. For general purposes, the carbon composition type has been used for many years and is therefore known to have an acceptable long-term stability for domestic and many commercial purposes. Changes in resistance under normal working conditions may be of the order of 5 per cent, but in more severe conditions, such as those encountered in the Services, changes of up to 25 per cent may occur. It is found that changes caused by high temperature (due either to ambient or self-generated heat) result in a permanent increase in resistance value, while exposure to high humidity increases the resistance, but the effect is largely reversible. The stability of wirewound and cracked-carbon resistors is much higher—of the order of 1-2 per cent. Metal film resistors are comparable in stability to the wirewound types. This 6 ELECTRONIC COMPONENTS, TUBES AND TRANSISTORS stability is dependent mainly on the protection afforded to the resistive element by sealing. Even under the severe conditions encountered in the Services, changes are not usually more than 2 per cent. Oxide films have a stability rather better than that of the cracked-carbon film. Rubberized Wound with End Cap Nickel-chrome Tube Insulated or Copper-nickel Brass Tube, Internaliy with- -Enamelled Wire Stannaie Tinned Oiled Paper 20SWG Sleeving TC Wire - over Connections Ceramic Insulating Metal ..** Former Disc (2Holes) Moulding FIG. 1.7. Wirewound (precision) type. The highest stability with lowest temperature coefficient is still obtained with wirewound precision resistors (see Fig. 1.7), although some of the evaporated metal film resistors approach this but do not yet equal it. Accuracy {or Tolerance) Carbon composition resistors are made to approximate target values and then selected to various values after manufacture. Selection tolerances are set up and resistors sorted to ± 5 per cent, + 10 per cent and + 20 per cent of the nominal batch value. Carbon composition resistors cannot be regarded as accurate to better than 5 per cent because of the lack of precise control in their composition and because of a tendency to drift in value. Pyrolytic or cracked-carbon resistors are accurate to 1 or 2 per cent, but can be manufactured to about 0-1 per cent if necessary. Wirewound resistors are accurate to 0-25 per cent and can be manufactured to 0-05 per cent or even 0Ό1 per cent if desired.