Punch X360.2 schematic / advice

Good question. Aparrently neither. But the drive waves are going nuts above 13.6. Here are gate and drain waves respectively below 13.6, and above 13.6.

In both cases, audio is passing and rail voltage is steady.


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Did you re-set the bias?

This is a regulated power supply and the supply will roll back the duty cycle as soon as the rail voltage reaches the target rail voltage. If nothing is pulling the rail voltage down (no bias current or power output), the duty cycle will go to near 0%. You will see the drive better on pins 9 and 10 of the 494.
Curious about the regulation aspect so I ran a test. It is unregulated under 13.8 volts B+ based on the clipping / max output being proportional to B+. But it starts limiting the rails above 13.8v B+. It appears regulation doesn't start happening until B+ (or rails) goes above a certain limit. It's regulating down for a higher B+, but not up for lower B+. I would call this a limiter more than a regulator, at least in the sense regulation doesn't happen unless B+ is high enough.
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It's not generally practical for the transformer winding ratio to be so high that it can reach the target rail voltage at any DC input voltage. Some amps do it but it's not generally practical.

With the regulation that this amp has, it limits the rail voltage to a point that the output transistors won't fail due to having to dissipate more power than they can handle.

In some amps, the regulation prevents the rail voltage to go above the working voltage of the rail caps. This allows them to use the highest possible capacitance. This amp uses 50v caps so voltage isn't a concern for the caps.