Eico HF-20 questions?

I've still got a single amp here, one of these days I'd like to match it up, or at least
the output transformer and make a nice pair of amps based off of them, I've got an
pair of chokes with the same potting cans, should make for some impressive looking
and hopefully sounding pieces of audio.
(I know that output was used on a few models, mine is the one stamped on bottom)

Congrats..:thmbsp:

HF22, HF35 and HF20... that's what you need. IIRC, the HF20 and HF22 use the same power transformer, too...

Regards,
Gordon.
 
That can happen. All it takes, is unbalanced output tubes (different gain or transconductance), to cause a differential in current draw through the output transformer, which can allow reproduction of hum from the power supply. Normally, with balanced tubes, this sort of thing 'cancels out'... if each tube draws the same, any noise in the PS is essentially balanced/cancelled by the out-of-phase nature of PP output tubes. But, if one is significantly stronger than the other, you can pick up hum that way, due to a net current differential of one tube, over the other.

The exact substitution may be entirely incidental (you could probably have used matched pairs of 6L6s of any type)... but it's great that you found a pair of tubes that work well in each amp!

Regards,
Gordon.

Thanks for the information Gordon, I appreciate it! I am going to replace the four filtering caps and the 50/50 electrolytic in the bias supply but that's about it.
 
I've still got a single amp here, one of these days I'd like to match it up, or at least
the output transformer and make a nice pair of amps based off of them, I've got an
pair of chokes with the same potting cans, should make for some impressive looking
and hopefully sounding pieces of audio.
(I know that output was used on a few models, mine is the one stamped on bottom)

Congrats..:thmbsp:

Well I just happen to have a very nice HF20 sitting right here. Real clean and all original.

Shoot me a PM.

WO
 
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