Amp warm, set at full power, all of the controls turned counterclockwise, biasing set to 60 mVolts and balanced at .ooo. Now, if you turn the tremolo intensity knob up (clockwise), the biasing voltage surges to over 300 mvolts, and the power tubes will begin to overheat. The intensity knob is the only thing that causes this to happen. Already replaced all tubes and have the same result. Any thoughts???
Depending on the model, the vibrato adjusts the output grid bias rather brutally, like the Ampeg Reverberocket did. If you check the anode voltage on the optocoupler drive, that may give you a clue. If it goes too low, so will the bias voltage and the output 6L6's will over dissipate. Some techs reduce the bias current but I prefer to replace the anode load resistor on the multivibrator or optocoupler.
If it says 2002 on the main board, that sounds like a revision E board, yes?
Are BOTH sides equally affected?
What is the bias voltage at the grids of the power tubes doing?
Does it matter if the trem is ON or not?
C112-115 couple the trem signal from the +250v trem circuit down to the -60v bias. One of them leaks, and you cancel some bias. So what voltage sits at the top of the intensity pots?
Check the intensity pots for open segments.
Are BOTH sides equally affected?
What is the bias voltage at the grids of the power tubes doing?
Does it matter if the trem is ON or not?
C112-115 couple the trem signal from the +250v trem circuit down to the -60v bias. One of them leaks, and you cancel some bias. So what voltage sits at the top of the intensity pots?
Check the intensity pots for open segments.
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