A concise guide to Power Valve Amplifiers. Part 3.

 

Smoke and mirrors. Why spending cash to replace electronic circuit components with expensive, exotic ones is a pointless exercise. Geoff Kremer pens his views.

 

"The following is as result of my own experience and recommendations.
I am not in any way suggesting that expensive components will not 'do the job', but what
I am saying is that good quality off-the-shelf parts will work equally well".

 

To be blunt, a valve amplifier can be only as good as it's internal power supply and it's output transformers, but even with the very best of these, poor circuit implementation can ruin everything.

Almost all valve amplifiers can be improved by optimising their operating characteristics, but replacing various internal components with so called “state of the art' parts will have little effect. As an example of what I am saying, I can give an account of an amplifier I worked on early in 2012, but I must stress that this is by no means an unusual case:
 
A client brought in a US manufactured ”Canary CA-608” integrated valve amplifier. I hold these amplifiers in high regard and consider them to be one of the best valve amplifiers manufactured in the States. The client was complaining of a buzz on one channel. He'd  recently purchased it brand new from a dealer in the US, and at the same time had been persuaded (by the dealer) to have upgraded components installed at an additional cost of $3000.
 
Testing the amplifier revealed quite a loud buzzing on the left channel, a screaming sound on switch off and a rather dull, uninteresting sound quality. Certainly not up to the expected quality from Canary. Opening the amplifier revealed a cornucopia of very pretty, mostly gold and red capacitors and huge, thick, very very expensive cabling.
 
I explained to my client the grave reservations I had of these modifications, and suggested, to the utter dismay of my client, that I reinstate everything back to the manufacturers original specifications. I'd be utilizing off the shelf parts to replace the weird and not so wonderful ones fitted by the dealer, and then optimise the circuit for best performance.  At least the exercise was made easier because the original wiring had been left in place, just disconnected.
 
The result was immediately apparent by a huge audible improvement. The buzz and scream had also completely disappeared. Once I had optimised the phase splitter circuit for minimum distortion, I thought the amplifier really sang.

The sub-chassis of Geoff’s Proteus 4040 valve power amplifier. The discrete components are good quality but easily sourced “off-the-shelf” items.

 

I don’t attribute the previous poor performance to the expensive parts, just that they had represented terrible value for money. In the case of the Canary, the reason why I took out all the new parts was mainly because they were so physically big and badly fitted. Yes, it was mostly poor workmanship causing the problems, but also the size of the new parts meant that they were picking up radiation. The cabling was so thick, it couldn't be properly dressed into place to avoid interference.

 

Lesson. If you own a valve amplifier that you would like overhauled or wish to overhaul yourself, please avoid the trap of replacing various parts with vastly over priced and overrated “high grade” components. Good quality off the shelf items will work every bit as well. I can recommend components from Vishay, BHC, Evox-Riva, Welwyn and LCR. All these can be easily obtained from RS Components and Farnell.

Below, verbatim, is the email I received from the client when he connected his amplifier at his home:

"Good morning Geoff,

Amp arrived yesterday and I was delighted to have an afternoon's listening to a clear, detailed and 'full' sound, with no nasty 'screeching' on switch-off. Many thanks for the 'magic' worked and the additional box of bits (which I will work out what to do with at some time) - even Fiona says she can hear the difference!
 
Once again, many thanks.
 
Keith".

With thanks to the author Geoff Kremer of English Valve Amplifiers Ltd. and Servicesound for this article.

 

Read part one: Triode, Tetrode and Pentode valves.

Read part two: Class A, Class B, Class AB and Bias.