Mike,

Try this: Lift up D15 or 16 diconnecting one end from the board. Solder the
center and one end of a 47 ot 100 Ohm preset between the two diodes.
Make sure the preset is at minimum. Power up and slowly increase the
preset till distortion goes away.See that the Q72/73 don't get hot while
the volume is low.

You are increasing the quiescent current in the final transistor to overcome
cross over distortion.
https://en.wikipedia.org/wiki/Crossover_distortion


Raj

At 16/06/2018, you wrote: