audio amplifier dc offset right channel is -1.8V and one power transistor is hot.

Heathkit AR-1500 receiver running hot on right channel with high dc offset measured at the speaker terminal. Output amplifiers on both channels is symmetrical with two differential amps with driver transistors, dissemination limiter transistors and output transistors working off of 43V +- rails. I am trying to determine what is causing the high dc on the output which I assume is causing the heating. Speakers crackle slightly otherwise the receiver sounds good. I have read that the transistors in the differential amplifier could cause this if they are not matched or their base currents are unequal. Suggestions welcomed.

by gwinn
February 17, 2024

Check the capacitors! If their top is not flat anymore, they are dried and not working as capacitor anymore, they are not blocking DC anymore, they are more a resistor than a capacitor.

by vanderghast
February 19, 2024

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