Valve amp suggestions for Harbeth 40.1

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You rang?
Simple answers: possible? Yes. Sensible and cost effective? No.
Basically, the component cost that matters with serious valve power amps is primarily transformers, and they cost. Changing from capacitor coupling to interstage would be a serious undertaking and obviously would need suitable transformers. You could get them hand-wound (Dave Slagle in the US among others), but that takes time and many beer tokens. Various companies produce suitable iron, but for an example, a pair of suitable Tango (now ISO) or Hashimotos will be about 1000 euros. Then, you'd need to look at the circuit. The driver stage will need to be revised to drive the tubes properly, not to mention that a pair of interstage transformers are very unlikely to fit in the existing chassis.
Fot output and mains transformers, the problem of size may be less of an issue, but the problem of cost won't be. To better what you already have, you're probably looking at around 1500 euros for output transformers. Sowter will custom wind mains transformers, but that doesn't come cheap either. Go mad off the Audio Note price list and you could quite easily spend upwards of £25000 on a pair of output and interstage transformers. Or at least, you could have, but you can't at the moment because they've stopped supplying parts to concentrate on their own builds.
Of course, you can get lucky. For my (yes, I know how long it's taken) 300B PP build, I managed to score a pair of new Hashimoto output transformers from the US distributor at half list, as a cancelled order. I also got (very) lucky with the exchange rate and timing, and got a pair of Slagle interstages hand wound that ended up around £450 landed here, but add the £1200 or so that I spent with Sowter and the iron alone still comes to a serious lump of cash.
Basically, if you're building from scratch, it makes sense. However, economies of scale mean that this is a case where trading up is going to be much better value. Especially as seriously modified equipment will not show a good return come resale time.
For 'sensible' upgrades, change capacitors and valves for better types. Otherwise, sell up and buy something better. Or keep what you have and buy more music  :cool:


Okay scratch that idea off the list! You also made a good point re second hand value Richard

Thank you for the helpful reply!

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I borrowed an old Dynaco ST70 from my dad and am listening to it right now in my system. At 30W/channel I was not expecting much, but I have to say that I am mightily impressed, for a relatively budget 60 year old amp it is astounding. It does not quite have the dynamics, scale or soundstage as my Icon Audio’s, but the midrange is great and works a charm with the 40.1’s. when things get busy the presentation can get somewhat congested as expected, but I cannot hear any distortion to speak of. If I had to live with this amp I wouldn’t cry myself to sleep every night.

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