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In Reply to: RE: insufficient range on bias pot scott 299b posted by thermionic emitter on July 12, 2016 at 22:39:37
because I'm seeing more blue at the top then normal..What you most likely need to do is take out the old selenium bridge rectifier and put in a silicon bridge to get the negative bias voltage higher.If it was changed,look at the 75v filter caps on that one can.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 07/13/16Follow Ups:
If he changes the set bias voltage to -15VDC, he can only bias to 30mA per pair of 7189. That seems to be too cold if 420VDC is the plate voltage (6.3 watts per tube).
What is the plate voltage onto those output tubes?
I thought he said it was only minus 11vdc,that would make it too hot.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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