02-17-2021, 01:04 PM
If the majority of the capacitors have not been replaced then it time to do that.
Hot AF output tubes are a sign of incorrect bias. Check C32, 33, 34 for leakage, C36 and the dual C37. Confirm the value of R30 and its connection to the chassis. That causes a high plate current and overloads the power supply so it begins to hum, the caps in the supply cannot make up for the high current flow so 120hz ripple results. The 6K6 can be permanently damaged if it is severely overloaded, emissive material will get deposited on G1 and the tube will loose control over the plate current. YMMV chas
Hot AF output tubes are a sign of incorrect bias. Check C32, 33, 34 for leakage, C36 and the dual C37. Confirm the value of R30 and its connection to the chassis. That causes a high plate current and overloads the power supply so it begins to hum, the caps in the supply cannot make up for the high current flow so 120hz ripple results. The 6K6 can be permanently damaged if it is severely overloaded, emissive material will get deposited on G1 and the tube will loose control over the plate current. YMMV chas
Pliny the younger
“nihil novum nihil varium nihil quod non semel spectasse sufficiat”
