Lucky me, I've got one of these. It is a late 60s, thin wire, silver face twin reverb. It is a real HUM dinger. argh! Been through caps, all electro's all around, that helped, some. Isolated to the power supply, with only the PI tube, and the PI feeder cap removed. Hum; Heater voltage is high, about 6.6VAC (123 VAC from the wall) However with the heater supply wire disconnected from the first power tube socket, it is still about 6.6VAC across the two wires. Interestingly then there is 193VAC and 187VAC to ground from each heater wire (still disconnected from the tube sockets). Now with a NEW/spliced in power tranny, hum (120 Hz) is reduced... and there is about 10.3VAC to ground from each heater wire. Measuring the 100 ohm resistors (heater side, lamp to ground [both with and w/o the bulb]) ...reduces the hum somewhat more. With PI cap installed and pre amp tubes , same hum @ 120 Hz, however it permiates the amp...and slighly varies with volume and tone controls too. So, where is it coming from? We know still in the power supply is the source. Replaces all the PI compnents...prior to New power tranny spliced in. HOWEVER Before I was going to rebuild the output tube socket components etc, and all related original wiring (no tube socket component is the same, three prong intallation is barely passible, not so hot, etc) I was hoping to trouble shoot the hum before continuing. Thinking now, I guess not, perhaps the problem is sloping component intall in the power tubes or the 100 ohm resistors at the lamp. I spliced in another choke too, that made no difference. All diodes have been replaced and bias upgraded as well. Fornication, I hate thinking I have to redo the output socket compopnents then still have the same problem with hum. I know I'm going to do that any way, I'd prefer to find the probem before continuing. Have I missed anything? Are there anythings you can think of that I've overlooked?