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In Reply to: RE: Fixed bias problem, and no, it is not the tubes. posted by Acoustic-Dimension on January 12, 2017 at 00:50:04
And it slowly declined after about 5 minutes. The coupling caps are 2 brand new Mundorf Silver and Gold in oil. The voltage rating on those are 800vdc so i seriously doubt that it is defective. The 10R resistor is a 2 watt unit and i did check it at the same time and it was not even warm, so again, doesnt appear to be a problem.
Follow Ups:
There is your problem. You have to check the bias voltage not only at the end. Where you find the decline, there is your bad part. Never assume good parts cannot be bad.
When I read the other answers you gave in this thread, I realized that it could not be the things I mentioned, because both sides (left and right) behave the same.
So it has to be something different.
Then I read your answer that the bias transformers gets hot
And that should not happen.
So I would replace the transformer.
Hi AD, i have 2 tx in the circuit, the filament trans and the choke. The filament tx gets warm and hot at about 30 minutes of use (i noticed the heat during the first few times i powered up the amp and now i notice that it gets warm after about 5 minutes) the choke is cool. My feeling is i should try a different fil trans.
AD has a point. As the transformer heats up the DCR is drifting. Perhaps check your connections first as you said it was fine in the shop.
That the bias transformer heats up can be a problem of the transformer, but could also bet hat one of the capacitors in the bias supply is not good (internal leak) so the bias transformers has to deliver some current.
Edits: 01/12/17
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