Lockdown Valve Amp

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SteveTheShadow
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Lockdown Valve Amp

Unread post by SteveTheShadow »

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.
Image
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.
Last edited by SteveTheShadow on Sun Apr 05, 2020 11:29 am, edited 2 times in total.
These users thanked the author SteveTheShadow for the post (total 2):
savvypaul (Sun Apr 12, 2020 1:04 pm) • Alfi (Sun Apr 12, 2020 9:08 pm)
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Re: Lockdown Valve Amp

Unread post by savvypaul »

:romance-hearteyes:
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Re: Lockdown Valve Amp

Unread post by slinger »

That is a rather tasty bit of DIY. :o
Amps - NVA P50, AP30, A40, Stanislav Palo Tube Headphone Amp BB 85
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Latteman
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Re: Lockdown Valve Amp

Unread post by Latteman »

That’s fantastic
Why do valve amps use the ‘block’ transformers?
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Re: Lockdown Valve Amp

Unread post by valvesRus »

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.

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SteveTheShadow
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Re: Lockdown Valve Amp

Unread post by SteveTheShadow »

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 :)
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Re: Lockdown Valve Amp

Unread post by zebbo »

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. :cry:
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Re: Lockdown Valve Amp

Unread post by Daniel Quinn »

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.

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Re: Lockdown Valve Amp

Unread post by zebbo »

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.
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Re: Lockdown Valve Amp

Unread post by Alfi »

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?


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