HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Like one or two others on here, I too have been at it with the DIY. I built myself a nice, 6W, single-ended KT77 valve amp out of bits I had lying around. No new bits were involved in this project. The blue transformers were painted with an old can of smooth Hammerite, I found in the cellar. The wood chassis housed the OTL. I just lifted out the OTL chassis after disconnecting it and dropped this one in its place.

It uses separate power supplies: one on the output stage, fed from the blue mains transformer, silver choke and large 5U4G rectifier valve at the rear right, and another, on the input stage, fed from the other blue mains transformer, and small EZ81 rectifier at front right. The choke for the input stage supply is under the hood, just behind the EZ81.

The pair of Genalex reissue KT77 pentodes are triode wired and fed by the pair of parallel strapped, 1960s, Hitachi 6SL7 twin triodes at the front. It partners the single driver Fane speakers nicely and gives a big, warm, detailed and musical presentation.

That is a rather tasty bit of DIY.

That’s fantastic
Why do valve amps use the ‘block’ transformers?

Latteman wrote: ↑Sun Apr 05, 2020 4:21 pm That’s fantastic
Why do valve amps use the ‘block’ transformers?

It's not compulsory, but there does seem to be a lot more of them on the market suited to the voltages that valve amps need.

I myself have several DIY valve amps using toroidal transformers.

Thanks for the comments chaps. It must be knocking on 15 years since I last built one of these single ended, two stage EL34/KT77 type valve amps. Full circle is the operative phrase I think

I do envy you guys with this knowledge and ability.
Quite a few years ago I did an evening class on electronics and even the simple stuff left me baffled. It was weird, as I could normally pick up stuff very easily and have always been able to turn my hand to almost anything. Just not for me I guess.

Learn empirically , that's what I've done. I dont understand half of what I do , but I know what sounds good and bad.

For instance , I haven't got a clue why a larger transformer and caps make the phone stage better but I can bloody hear it.

Yes, that may have been the problem previously. I was always there asking "yes but why?" or "yes but how?" and when they gave me the answers I found it difficult to comprehend. A case of too much too quickly maybe.

Daniel Quinn wrote: ↑Mon Apr 06, 2020 11:13 am Learn empirically , that's what I've done. I dont understand half of what I do , but I know what sounds good and bad.

But that's costly and potentially dangerous.

Daniel Quinn wrote: ↑Mon Apr 06, 2020 11:13 am
For instance , I haven't got a clue why a larger transformer and caps make the phone stage better but I can bloody hear it.

Doc stated in an interview with Audio arts magazine in 1992 that he could hear ripple and is why he kept cap value to a minimum, (which surprises me) as I always thought bigger cap value = more instantaneous reserves of power = better transient response?


Alfi.