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Original Message
Now it's back to its bad ways.
Posted by DAK on January 12, 2017 at 16:41:41:
Well, i put in some KT90s that test really strong and that i have used many hours with no problems, and the bias current started to run away again. The bias voltage also was dropping so there is definitely something going on. The problem is affecting both channels so it must be something from the filament trans to the 10K resistor, since both circuits at the pot seem to be affected equally. I think i will try a new filament trans.
I was checking my filament transformers and i have one that is 6.3v @ .5A. Is this trans ok for my circuit? Which would require enough current to bias 2 x kt150 tubes.