Tube DIY Asylum

RE: Also, anyone addressed the high B+ issue on the 208

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DAK

In Reply to: RE: Bias adjustment? Scott 208 posted by DAK on October 20, 2024 at 08:15:51

Like I mentioned previously I am running the amp through a variac to keep the B+ at sane levels and not wear out the Westinghouse 7591 tubes, because they are so pricey. I was wondering what modifications were done specifically on this amp since it is quite compact and space is an issue.

Follow Ups:

RE: Also, anyone addressed the high B+ issue on the 208 - Tre' 07:43:33 10/21/24 (4)
The problem is, knowing what the bias voltage is doesn't tell you what the idle current through the tubes is. High idle current through the 7591s is what will wear them out. I would start by putting a 10 ohm resistor in the cathode of each of the output tubes so you can know what the current is.
Current = voltage / resistance

Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
- What pin on the 7591 do I put the 10R resistor? ntd - DAK 12:10:45 10/21/24 (2)
  Alas.
  - RE: What pin on the 7591 do I put the 10R resistor? ntd - Tre' 13:02:53 10/21/24 (1)
    Pin 5 to ground.
    .
    Have Fun and Enjoy the Music
    "Still Working the Problem"
    - RE: What pin on the 7591 do I put the 10R resistor? ntd - DAK 13:17:31 10/21/24 (0)
      On the cathode pin. Now it is coming back to me. Lot of dust and cobwebs up in the old noggin, nowadays.
- RE: Also, anyone addressed the high B+ issue on the 208 - DAK 12:00:19 10/21/24 (0)
  Ok, I think that would be a good thing to do. Thanks for the suggestion.

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