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Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates, B.Sc. Reader Services Ann Jenkinson Sharon Macdonald Advertising Enquiries Leo Simpson Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Marque Crozman, VK2ZLZ John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Philip Watson, MIREE, VK2ZPW Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $49 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. PUBLISHER'S LETTER Valve amplifiers are dead & buried Every month we receive suggestions and requests from read­ers for a whole range of projects. Some of these are practical, some are too specialised for us to consider and then there are the occasional letters asking about valve amplifiers. Because people see glowing references to valve amplifiers in hifi maga­zines, they ask if SILICON CHIP has done or will be doing an article on a buildit-yourself hifi valve amplifier. Now when I read or hear about some of the things said about valve amplifiers in hifi magazines, mostly those from overseas I might add, my comments tend to become derogatory in the extreme. This is because I feel that articles promoting valve amplifiers are just plain dishonest. Let’s face it, valve amplifiers were once the “state of the art” and many people, myself included, built valve amplifiers and gained immense pleasure from them. But that was then. I can state right now that SILICON CHIP will never publish a design for a hifi valve amplifier unless it is for academic interest only. In fact, let’s be even more absolute and just say NEVER. There are three reasons for this stance. First, valve amplifiers of “reasonable” power output and quality are extraor­dinarily expensive. Typically, we could be talking about a kit cost of $1000 or more for a valve power amplifier capable of producing only 30 watts per channel. Second, such a “reasonable” valve amplifier would be no match at all for even run of the mill solid state amplifier modules. Take the 25W module published in the December 1993 issue for example. Using the cheap LM1875 module, it has a signal to noise ratio of 110dB and a distortion of around .025%, figures that blow virtually any valve amplifier ever designed out of the water. And remember, there’s nothing really special about the LM1875. Apart from that, valve amplifiers have several other big disadvantages. They run very hot, their valves are often micro­phonic and, the biggest disadvantage of all, they wear out. While a solid state amplifier can easily run for 20 years or more without anything wearing out, valves need to be replaced quite frequently if they are to give the best performance and this applies particularly to the output devices. And that brings me to the final disadvantage – availability. Good valves with a perfor­mance equal to the original published specifications are now virtually unobtainable, at any price. So unless you are an eccentric millionaire with a taste for esoteric hifi gadgetry, you can forget all about valve amplifi­ers. And don’t take any notice of comments about “special valve sound quality” or “gentle overload”, or other such rubbish. All these are just ways of describing valve distortion. So by all means enjoy reading about and perhaps even re­storing valve equipment. That’s nostalgia. But valve amplifiers have no place in today’s technology. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip