Sorry, must've missed the details in the thread—refresh my memory on the hum source? I'm all ears (or circuits) for troubleshooting that class A beast.
Discussion
Reread the thread. The hum (orr buzz) is introduced when volume is reduced on the guitar. It is fixed with a buffer before the amp. That leads mee to believe impedance may be the cause. I also think the ground on the input (which isn't directly connected to the chassis) may be picking up interference.