Originally posted by gui_tarzan
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And your bias should be much higher, stock bias is -48V with lower plate voltages, if you had -21V bias I would expect the power tubes to be red-plating.
If the cathodes are not grounded, that would also increase the B+.
What are the voltages at pins 3,4,5, and 8 of the power tubes? And the voltage across one of the 470 ohm resistors that connect to pin 4?
Edit: make sure the bias filter cap is 100V, not 50V like your drawing shows. + end goes to ground. 47uf rather than 25uf is commonly used.
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