Discover those classic audio gems.
Geoff has been an electronics service engineer for over 40 years specializing in the repair of valve amplifiers and reel to reel recorders under the Servicesound brand he founded in 1968. There's no doubt about it, Geoff is very passionate about valve amplifier design and technology, but with firm, very grounded views about Hi-Fi equipment and the Hi-Fi industry today. Let's face it, by anyone’s assessment, the industry is a complete mess with polemic views about what's significant or just a con, bizarre telephone number prices, and claims entirely contrary to the laws of physics.
Geoff holds great store by amplifiers designed and built from the mid 40's-70's, and has chosen to work with the Williamson landmark design as a blueprint. Of course there are benefits to employing modern components and production techniques, which is exactly what he’s done. I began by asking him:
Why the 1947 Williamson design in particular?
I had my eye on the 1947 Williamson push-pull amplifier design for some time. I hadn't ever come across an amplifier which followed this design closely, and in fact I don't think one had been produced for 20 years, so I decided to build one myself. I had the transformer hand-made to the Williamson design specification, and constructed the initial amplifier using the EL34 output valves. The results were extraordinarily encouraging, so I experimented with an improved version of the transformer, a more appropriate driver stage, and upgraded the valves to KT 88's. However, with a 600 volt HT supply, the KT 88’s didn't last too long, so I tried KT 90's. These tightened up the LF up nicely, working well within their capacity, but when the KT 120's came along, these were better still. So the Proteus 4040 amplifier evolved, and it still uses the Williamson designed output transformer.
What about the 300B and 211 valves. Aren't these currently the most highly regarded valves to use?
I have absolutely no idea why the 300B is ever used within an audio amplifier. This valve was designed and intended to be buried in the desert for 50 years, solely for telecoms use. I don't even like the sound of it. Beautiful sounding single-ended valves would be the GEC PX 25 and PX 4, specifically designed for audio use. The 211 and 845's are good but are basically transmitter valves and these need an HT supply of well over 1000 volts. Having said that, a valve is just a valve, and my transformers can accommodate this requirement in single-ended mode, so I think I'd be quite interested in making a low wattage, single-ended design using the 211 valve. I look forward to giving this a try.
Why did you decide to build an amp in the first place?
I was under strict instructions to “tidy up the Hi-Fi area”. Sounds familiar? I opted to make a single unit, Class A, high-end integrated amplifier which would include a phono stage. It was a hard task to incorporate all this in a single chassis with HT and LT supplies and a low level phono stages next to each other, but I got there in the end. Ideally, I would have liked to incorporate a moving-coil phono stage as well, but owing to noise problems, this was a step too far . I'm currently working on a separate valve moving-coil phono preamp which is progressing nicely, and this will be available soon.
On a completely different tack, I'm also very much into exploding Hi-Fi myths. All this business of using esoteric speaker cables, exotic oil-filled capacitors, silver wiring and so on is just smoke and mirrors, and very expensive ones at that. Making an amplifier without using outlandish components, but one which had all the detail and finesse one could hope for was my aim, and prove my point of view.
That's pretty controversial. Did you try exotic components but without any noticeable improvement?
There was absolutely no need to. No measurable benefit exists with the use of weird and wonderful components or exotic materials for cables. There may be a marginal advantage insofar as an oil dielectric in a capacitor can handle very high voltages, but for audio purposes, this is not necessary. I have been a service engineer for valve amps for over 40 years, and I've regularly had to reverse expensive component “modifications” made to amplifiers.
Frequently, not only had spurious noise been introduced into the circuit, but the sound quality was just plain bad after the “improvements”. In all honesty, after you've paid £3000 to have an amp modified, you want to hear that the sound is better. It takes a little while to realise that the changes have been a retrograde step. I'm certainly not alone in this thinking. The famed amplifier designer, Tim de Paravicini of Esoteric Audio Research, doesn't see the need to use exotic components in his amps either.
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