OTL Asylum

I just saw that you are having problems with Beveridge amplifiers

108.28.89.140

Lew

In Reply to: RE: Futterman posted by AJ on March 06, 2024 at 05:04:12

First, those could well be the very same H3aa's that I once owned. No way to be certain. I sold them to a guy who drove to DC from NYC to pick them up, about 25 years ago or more.

Second, I have extensive experience debugging the 2SW amplifiers shown in your photo (which is to say making them work without oscillating). If you haven't yet fixed your problems, I would be glad to help.

Follow Ups:

RE: I just saw that you are having problems with Beveridge amplifiers - AJ 05:17:07 06/24/24 (1)
Thanks Lew,
You and I have been conversing by email a few times regarding these.
Your trick to add a CC resistor between the cathode and heater also was helpful.
For others, the transformers in both Beveridge amps were electrically leaking and I had to design new transformers. This time separating the the HV from the filaments and pre--resulting in 2 transformers Solving the problem.
Some before and after pics.

Edits: 06/24/24
- RE: I just saw that you are having problems with Beveridge amplifiers - Lew 14:39:40 08/17/24 (0)
  AJ, On that same one of my two amplifiers that was oscillating, I not only inserted that 100R buffer between the cathode and the filament on (I think it was) V202, but I also installed a separate 36V transformer specifically to replace the filament supplied to that one tube (V202) from the Bev PT. In fact, bypassing the filament supply from the main PT to V202 (one of the three separate 36V filament supplies that come off the main PT, as you know) did the most to reduce oscillation. But the coup de grace for the oscillation was adding that 100R resistance. My other amplifier has no such problems, I think because somewhere in its life before I got it, it received a new PT. Certainly it's newer than the one having problems. Yes, I agree there seems to be leakage between the HV tap and especially this one of the three filament supplies.

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