Reduce Overheating of an old Audio Video Receiver - Harman/Kardon 3500
To minimize crossover distortion and variations of NPN+PNP Vbe drops, they use a pot.
Locate the Test points and measure with a voltmeter.
This represents the current through a 0.33 OHm resistor and also the transistors.
It may indicate a fault or just too high a setting.
I found the service manual online.