The M60 uses a self-bias circuit, which uses the current through the tube to develop the bias voltage. This type of circuit typically does not produce as much max power as a "fixed bias" one (the kind where the owner or an active circuit periodically adjusts the bias to a specific value), but they are inherently stable, and you can plug and play a variety of tube types, as long as they are matched.
Also, this amp idles at 160 watts per channel, and uses 280 watts at full power, so it's class AB, but conducting pretty well at idle.
Also, this amp idles at 160 watts per channel, and uses 280 watts at full power, so it's class AB, but conducting pretty well at idle.