Valve Amplifiers, Fourth Edition

798 Pages·2012·15.09 MB·English

by  Morgan Jones

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
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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.