Just a little hint in case somebody has the same amp humming: In my case, the hum reduced quite significantly after checking the gound connection to chassis: unscrew, scratch and clean the contact areas on both chassis and ground terminal and inserting a lock washer between the terminal and the chassis.
Now it is still not as quiet as some modern amps, but the hum is completely reasonable for an amp from that era.
Now it is still not as quiet as some modern amps, but the hum is completely reasonable for an amp from that era.
