Audiolab 8000A getting hot

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Bias is factory set by selecting R809 - R812. Bias should be 100mA. You have measured 90mA which is fine just aging of components.

Are you allowing sufficient room for cooling. You should have at least 150mm all the way around it, sides and top.

60 Degrees C is HOT for a Class AB amplifier, however, 40 Degrees above ambient is acceptable. During the winter some guys like to crank the heating up to 25 Degrees, this will make electronics run hotter, especially if the unit can't radiate the heat through being too confined.
 
It's unlikely to be anything to do with using headphones as the main power amp is still used, the headphone socket is across the speakers with a 390R resistor in series with it. Even short circuit headphones wouldn't cause it to overheat.

Could possibly be just dust build-up. Computers often fail when the fins of the heatsinks become clogged with "human".
 
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If the output stage current is OK and stable i.e. doesn't drift upward in value (you say it is OK) and the mains voltage is correct (is it adjustable, not set for 220 and used on 240 :)) then it's all normal.

There is no doubt... that's it ;)

If it's hotter than it should, then it's because the heat can not get away, not because of any circuit problem.
 
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