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Table of Contents Cover image Front matter Copyright Preface Dedication Acknowledgements Chapter 1 Circuit Analysis Chapter 2 Basic Building Blocks Chapter 3 Dynamic Range Chapter 4 Component Technology Chapter 5 Power Supplies Chapter 6 The Power Amplifier Chapter 7 The Pre Amplifier Appendix Index Front matter Valve Amplifiers Valve Amplifiers Fourth Edition Morgan Jones AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD • PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKY.
Table of Contents Cover image Front-matter Copyright Preface Dedication Acknowledgements Chapter Circuit Analysis Chapter Basic Building Blocks Chapter Dynamic Range Chapter Component Technology Chapter Power Supplies Chapter The Power Amplifier Chapter The Pre-Amplifier Appendix Index Front-matter Valve Amplifiers Valve Amplifiers Fourth Edition Morgan Jones AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD • PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO Newnes is an imprint of Elsevier Copyright Newnes is an imprint of Elsevier The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, UK 225 Wyman Street, Waltham, MA 02451, USA Copyright © 2012 Elsevier Ltd All rights reserved No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher Permissions may be sought directly from Elsevier's Science & Technology Rights Department in Oxford, UK: phone (+44) (0) 1865 843830; fax (+44) (0) 1865 853333; email: permissions@elsevier.com Alternatively you can submit your request online by visiting the Elsevier web site at http://elsevier.com/locate/permissions and selecting obtaining permission to use Elsevier material Notice No responsibility is assumed by the publisher for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions or ideas contained in the material herein Because of rapid advances in the medical sciences, in particular, independent verification of diagnoses and drug dosages should be made British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress ISBN: 978-0-08-096640-3 For information on all Newnes publications visit our web site at www.newnespress.com Printed and bound in the UK 11 12 13 14 15 10 Preface Almost 40 years ago the author bought his first valve amplifier; it cost him £3, and represented many weeks’ pocket money Whilst his pocket money has increased, so have his aspirations, and the DIY need was born Although there were many sources of information on circuit design, the electronics works gave scant regard to audio design, whilst the Hi-Fi books barely scratched the surface of the theory The author, therefore, spent much time in libraries trying to link this information together to form a basis for audio design This book is the result of those years of effort and aims to present thermionic theory in an accessible form without getting too bogged down in maths Primarily, it is a book for practical people armed with a calculator or computer, a power drill and a (temperature-controlled) soldering iron The author started a B.Sc in Acoustical Engineering, but left after a year to join BBC Engineering as a Technical Assistant, where he received excellent tuition in electronics and rose to the giddy heights of a Senior Engineer before being made redundant by BBC cuts He has also served time in Higher Education, and although developing the UK’s first B.Sc (Hons.) Media Technology course and watching students blossom into graduates with successful careers was immensely satisfying, education is achieved by class contact – not by committees and paper chases Early on, he became a member of the Audio Engineering Society, and has designed and constructed many valve pre-amplifiers and power amplifiers, loudspeakers, pick-up arms and a pair of electrostatic headphones It is now 18 years since work began on the 1st edition of Valve Amplifiers, yet much has changed in this obsolete technology since then The relentless infestation of homes by computers has meant that test and measurement has become both cheaper and more easily integrated, either because it directly uses the processing power of a computer, or because it borrows from the technology needed to make them Thus, the Fast Fourier Transform has become a tool for all to use, from industrial designer to keen amateur – enabling spectrum analysis via a £100 sound card that was the province of world class companies only 20 years ago As a happy consequence, this edition benefits from detailed measurements limited primarily by the author’s time Computer modelling is now freely available – exemplified by Duncan Munro’s PSUD2 linear power supply freeware The spread of Internet trading has made the market for valves truly global Exotica such as Loctals, European ‘Special Quality’ valves, and final generation Soviet bloc valves are now all readily available worldwide to any Luddite with the patience to access the Internet – we no longer need to be constrained to conservative (but expensive) choices of traditional audio valves Even better, many of the 1950s engineering books that you thought had gone forever are available from the second-hand book sellers on the Internet Paradoxically, although digital electronics has improved the supply of valves, other analogue components are dying Capacitors are the worst affected by the lack of raw materials; polycarbonate disappeared in 2001, and silvered-mica capacitors and polystyrene are both endangered species Controls have succumbed to the ubiquitous digital encoder, so mechanical switch ranges have contracted and potentiometers face a similar Darwinian fate It is particularly galling to discover a use for Zeners just as major semiconductor manufacturers stop making them Despite, or perhaps because of, these problems, valves and vinyl have become design icons, both in television adverts and the bits in between The relentless hype from manufacturers of audio servers that favour convenience over sound quality has forced manufacturers of CD players to justify their products on sound quality ( and convenience, because although nobody mentions it, a CD player is unable to wipe your entire music library at the drop of an operating system) CD and vinyl are now the only reliable sources of quality audio – which is perhaps a step forward from the 1980s when it was FM radio and vinyl Note for the MP3 generation: That shiny 120 mm disc was invented for storing music (such as Beethoven’s 9th Symphony) at far higher quality than a compressed download Try it some time – you might even like it Dedication The author would like to dedicate this book to the dwindling band of BBC engineers, particularly at BBC Southampton, and also to those at BBC Wood Norton, of which he has many colourful memories Acknowledgements Special thanks are due to Euan McKenzie who undertook the onerous task of proofreading at long distance on short notice and in record time to an appropriately low uncertainty Thermionic design cannot proceed in a vacuum, so the author is grateful for the perceptive insights and insults freely offered by Stuart Yaniger over the recent years An annual celebration of awe and wonder has been the European Triode Festival This delightfully civilised bacchanalia has humbled the author with splendid works of art and engineering whilst at the same time reassuring him that he was not alone Thank you, Christian, for first inviting me, and even more thanks to subsequent organisers for successfully maintaining the momentum Finally, the author would like to thank those readers who took the time and trouble to breach the publishing citadel and give the author hugely useful feedback resistance 490–491 , 493 transformer 483 valve 481 , 488f teething problems 494–497 valve biasing 483–484 screen grids 86–87 , 94 , 318 secondary emission kink 87 secondary emission ratio (SER) 320–321 second-hand equipment 660–662 see-saw phase splitter 458–460 selenium rectifiers 342 , 342f self-bias: cascodes 100f self-capacitance 277–279 semiconductor constant current sinks 139–153 , 146f design using DN2540 149–153 field-effect transistors 147–148 r out optimisation by transistor type 145–146 transistors as active loads for valves 142–145 semiconductors 42–45 balanced hybrid RIAA stage 629–630 reference noise measurements and statistical summation 232–234 series feedback 560f , 562f series/parallel networks: resistors 9–13 , 9f series regulators 378–379 see also fundamental series regulators ; two-transistor series regulators series resonant circuits 32f series switching 571f SER (secondary emission ratio) 320–321 shunt feedback 560f shunt-regulated push-pull amplifier (SRPP) 125–128 , 443–450 circuits 128f distortion 128 , 129f operating current 127f THD vs HT voltage 129f shunt regulators 378–379 shunt switching 571f signal amplitude 169–173 signal interference 409 silicon diodes 42–45 current against forward bias voltage 42f silvered mica capacitors 257 silver pins 329 sine waves: alternating current 21–24 amplitude 22 single-ended Class A output stage 436–438 sinks, constant current: 334Z constant current sink 521 balanced hybrid RIAA stage 643 bias 195–196 common cathode amplifiers 109–113 Crystal Palace amplifier 512–513 , 518–521 definitions 107–109 JFET cascode 152f operating conditions 110f pentodes 111–113 semiconductor type 139–153 design using DN2540 149–153 field-effect transistors 147–148 r out optimisation by transistor type 145–146 transistors as active loads for valves 142–145 Skirrow, Peter 160 slewing distortion 39 , 584 , 585f slope resistance 43 , 44t , 192t slugging the dominant pole 465–467 Small, R 438 small-signal pentode (EF86) 91–94 , 605 smoothing 334–378 high tension 485 single reservoir capacitor approach 343 SN7 valve family: electrical alternatives 205t heater voltages and currents 203t snubbers 361–364 , 502f sockets see valve sockets soft clipping 174f software: PSUD2 367–369 , 371 , 420–423 , 429–430 ResCalc 651 source followers 636t , 642–643 sources, constant current: cascodes 402f definitions 107–109 μ-follower 131f space-charge-limited condition: triodes 66 spectrum analysers 163 speed-up capacitors 382–384 split bobbin transformers 354–355 , 410f split RIAA equalisation 597–599 spreadsheets: shunt feedback vs series feedback 560f volume controls 558–559 sputtering 242 square waves: alternating current 34–35 response at 10▒kHz 215f sag/low-frequency cut-off frequency relationship 39t square wave sag and low frequency 654–656 time and frequency 34f transients 35–39 squegging 467 SRBP (synthetic resin bonded paper) boards 329–330 SRRP see shunt-regulated push-pull amplifier stabilised common emitter amplifier 48f , 49 stability 465–470 control grid-stoppers 468 , 469 dominant pole slugging 465–467 HF stability and chassis bond 469 LF instability 467–468 loop gain 465 motorboating 467–468 parasitic oscillation 468 anode stoppers 469 ultra-linear output stages 469 slugging the dominant pole 465–467 squegging 467 stability margin 469–470 standard component values 651 statistical regulators 399–402 , 402f , 403 , 403f , 404f , 418 , 419f heater rectification and smoothing 420 HT rectification and smoothing 420 optimisation 404–405 Stefan’s law 299–300 step: definition 35 step networks 210–211 stepped attenuators 561t , 563 , 564f stepped current feature: PSUD2 software 367f , 368 stereo crosstalk 397–398 stop-band frequency: filters 29 styli 656–657 suppressor grids 87–88 surface mount resistors 564f switched attenuators 554–555 design 555–558 Type A 555–556 , 555f , 566t Type B 555–556 , 555f Type C 555f , 556 , 565 switcher power supplies 333 , 334f switches: electro-mechanical switches 550–551 leakage resistance 550 mains 416–417 switch-on surge 415 symbols: circuit analysis 1–2 synthetic resin bonded paper (SRBP) boards 329–330 T tantalum bead capacitors 387–388 , 388f tantalum electrolytic capacitors 266 temperature see heat tertiary winding: transformers 25 test circuits 199–200 distortion 183f linearity test circuit 171f medium-μ valve 201f tetrodes 86–87 anode characteristics 86–87 , 88f grids 318 screen grids 86–87 secondary emission kink 87 see also beam tetrodes ; pentodes THD (total harmonic distortion) 90 , 128 , 158 , 162–163 thermal noise 40 thermal stability 521 thermionic emission 650–651 thermionic rectifiers 334–335 thermionic valves 295–299 electrons emission 296–297 velocity 297–298 history 295–296 transit time 298–299 see also anodes ; cathodes ; common cathode triode amplifier ; control grids ; pentodes ; tetrodes ; triodes ; valve choice/testing ; valve sockets Thévenin equivalent circuit 15–18 , 72f Thévenin level shifter 213 thick film power resistors 248 Thiele inductor formulae 273–275 , 275f THINGY (transistorised heater insulation noise grounding yoke) 405– 407 thoriated tungsten cathodes 299–300 , 302–330 time constants 30–31 tolerance: resistors 248 tone control 579–585 toroid transformers 282–283 , 282f , 350 total harmonic distortion (THD) 90 , 128 , 158 , 162–163 total network resistance 11 , 11f , 12 , 12f , 13–14 , 13f total parallel resistance: reciprocal of 10 tracking: resistors 243–244 transconductance see mutual conductance transformers 279–291 abuses/uses 291–292 , 293–294 alternating current 24–25 arcs 293–294 audio transformers 292–293 back-to-back arrangement for HT supplies 353–355 bifilar winding 283 C cores 281–283 , 282f choice of 292–293 , 350–353 copper losses 284 core saturation 350 coupling 210 damage prevention 294 DC magnetisation 283–284 eddy current losses 280 E/I cores 281 , 281f electrostatic screens 284–285 equivalent circuits 287f feedback 285–286 guitar amplifiers 293–294 high-frequency models 288–289 , 289f HT transformers 486–487 hysteresis loss 280 , 439 , 440 input transformers 289–291 inter-stage transformers 291–292 iron losses 279–283 leakage inductance 280–281 loudspeakers 285–286 low-frequency models 287–288 , 287f magnetic core deterioration 294 magnetic screening cans 294 , 295f magnetising current 353–354 , 355f magnetostriction 285 mid-frequency models 288 , 288f models 286–289 multifilar winding 283 potential dividers 290 split bobbin isolating transformers 354–355 split chamber 283 , 283f symbols 24f toroidal core arrangement 282–283 , 282f uses/abuses 291–292 , 293–294 voltage regulation 412 volume control 567–568 windings 283–284 Zobel network 290 , 290f , 291 see also output transformers transients: square waves 35–39 transistor amplifiers 351f , 500 transistorised heater insulation noise grounding yoke (THINGY) 405– 407 transistors: BC549 NPN transistor 131f BC558B PNP transistor 50f GET1 transistor 45f see also bipolar junction transistors ; semiconductor constant current sinks transit time: thermionic valves 298–299 triodes: 417A triode 86f , 87f as charge amplifiers 102–103 , 102f driver stage 452t dual triodes 452t , 481t GM70 125W triode 527 guided-grid triodes 85–86 noise from 225 space-charge-limited conditions 66 transconductance 614t see also common cathode triode amplifier tungsten filaments 295 , 302–330 turntables 591 , 656 two-transistor series regulators 381–382 , 381f , 496f Type A stepped attenuator 561t , 563 Type A switched attenuator 555–556 , 555f , 558–559 , 566t Type B switched attenuator 555–556 , 555f Type C switched attenuator 555f , 556 , 565 U ultra-linear amplifiers 446f , 469 ultrasound overload 593 , 594 units and multipliers 19–20 unity-gain cable drivers 635–636 US see American… V vacuum quality: valves 322 valve bases: leakage resistance against frequency 327f Loktal Base 326–328 valve choice/testing: 6SN7 family 202t , 204t 7N7 valve family 204t 12SN7 valve family 204t audio test level and frequency 200 conclusions 206–207 convention 205 distortion 196–207 distortion-weighted results 206 , 207t driver stage 492 electron deflection 198–199 envelope carbonization 198 heaters 619–620 interpretation 203–205 Loctal family 204t low-distortion valves 196–198 , 199 medium-μ valves 205–206 μ-follower 122–123 SN7 family 203t test circuits 199–200 test results 200–202 valve data 647–651 American valve codes 649–650 European Pro-Electron valve codes 647–649 pin connections 650 thermionic emission 650–651 valve noise 322 , 607 valve rectifiers 335–336 , 336t , 337 series resistance 348 solid state plug-in replacement 338f valve regulators see voltage regulators valve sockets: leakage resistance against frequency 327f losses and noise 326 valves, thermionic 295–299 electrons emission 296–297 velocity 297–298 history 295–296 transit time 298–299 see also anodes ; cathodes ; common cathode triode amplifier ; control grids ; pentodes ; tetrodes ; triodes ; valve choice/testing valve support circuitry: bipolar transistors 147t valve voltage regulators see voltage regulators V a(max) and positive HT supply 513–514 variable bias voltage regulators 384–386 variable-μ valves 317–318 V CE : balanced hybrid RIAA stage 638–639 V g2 ratings 525–527 vinyl records: cartridge output level 656 , 656–657 cut curve 595 , 596 , 596f digital comparison 585–586 equalisation 657–659 groove size 656–657 old/worn discs 594 pick-up arm mechanics 657 speed issues 656 see also analogue disc signal ; EC8010 RIAA stage ; RIAA virtual cathode 89 virtual earth adder 57–58 Volt: definition voltage: Kirchhoff’s law 8–9 see also V a(max) ; V CE voltage compliance 108 voltage drop, forward 43 , 44t , 192t voltage follower operational amplifiers 58–59 voltage multipliers 355–357 voltage noise 225 voltage rating 525–527 capacitors 269 , 413–414 , 413f , 414f resistors 243 , 249 voltage references 43–45 voltage-referred noise 233t voltage regulators 378–407 317 IC voltage regulator 386–390 amplifier stability 398–399 automatic voltage regulator 305 composite Zener bypassing 402–403 Crystal Palace amplifier 530f fundamental series regulator 379–381 , 379f gas references 392f , 393 , 395 heater supply elevation 405–407 hum cancellation 394 increasing output current 394–397 leakage current 405 Maida high voltage regulator 389f optimised valve voltage regulator 393–394 , 396f output capacitance 402–403 , 402f output current 394–397 output inductance compensation 384 pentode input 394 potential dividers 379f , 398 , 398f , 400f power supply output resistance 397–399 series regulator 378–379 shunt regulator 378–379 speed-up capacitor 382–384 statistical regulator 399–402 , 402f , 403 , 403f , 404f optimisation 404–405 stereo crosstalk 397–398 THINGY 405–407 transformers 412 transistorised heater insulation noise grounding yoke 405–407 two-transistor series regulator 381–382 , 381f valve voltage regulators 390–393 variable bias voltage regulator 384–386 voltage jumps 392 Zener diodes 382 , 401 , 401f , 402–403 , 404–405 Zener slope resistance 404f volume controls 174–175 , 175f attenuation error against attenuation 560f balance 565 Bulwer-Lytton amplifier 541–542 , 543t control value limitations 552–553 digital active crossovers 559–561 disturbing frequency response 552–553 grid-leak resistors 563–565 light-sensitive resistors 565–567 , 566t logarithmic law 553 , 563f noise 223–224 , 562–563 potentiometers 553 pre-amplifiers 551–568 quadrant faders 554 shunt feedback vs series feedback 560f spreadsheets 558–559 , 560f stepped attenuators 564f surface mount resistors 564f switched attenuators 554–558 transformer volume controls 567–568 W Walton, E.T.S 355 watt: definition 6–7 waveforms: reservoir capacitors 349f ripple current 347f weighting of harmonics 159–160 Western Electric harmonic equaliser 184–185 , 186–188 White cathode follower 114–118 analysis 114–117 as output stage 117–118 white noise 40 , 162–163 wide-band response: LC filters 375–376 Williamson amplifier 470–472 , 473f windings: Ayrton-Perry winding 247 transformers 24–25 , 283–284 windowing: fast fourier transform 167–168 periodicity 167f wirewound resistors 244–248 work: definition Index Z Zener diodes 43 , 193–194 composite Zener/317 IC regulator comparison 235–236 voltage and applied current against time 428f voltage regulators 382 , 401 , 401f , 402–403 , 404–405 Zener reference noise 234–235 Zener slope resistance 404f Zobel capacitance 617t Zobel networks 290 , 290f , 291 , 501–503 , 509f ... constructed many valve pre -amplifiers and power amplifiers, loudspeakers, pick-up arms and a pair of electrostatic headphones It is now 18 years since work began on the 1st edition of Valve Amplifiers, ... Analysis In order to look at the interesting business of designing and building valve amplifiers, we need some knowledge of electronics funmentals Unfortunately, fundamentals are not terribly... finding this directly, so we must look for a point where we can apply our rules We can apply only one rule at a time, so we look for a combination of components made up only of series or parallel