[Joeztech]

It looks like that 75pFd capacitor might be there to roll off the high frequency response. This may have been done to help protect the output transformer from extreme high frequency spikes. The output transformer has .003mFd capacitors on either side of the center tap on the primary windings for snubbing the spikes too. Make sure that those parts have about a 1KV or better rating.

As far as any effect on audible response, it probably would not be noticed as the frequencies affected would be in the ultrasonic range.

Joe