• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

high voltage after cap. change

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Looking at the schematic you need -45 volts for bias. The power tubes are crackling because they are getting warm. I also think your voltage meter is wrong. Unless you are plugging in to 220v with a 120v amp. Can you bring the bias up to spec.? Just for giggles see what your volt meter reads plugging it into your wall AC.
 
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