07-31-2019, 11:21 AM
I have been working on some amps lately and have found 3 cases of "tested good" used tubes that have high impedance shorts, most likely deposits on the micas. So watch for any red-plating - might want to watch in dim light - watch for unusual hum and or excessive current across the OP trans. Run the tubes for a couple of minutes and then retest for shorts even a slight flickering of the short indicator. Add cathode fuses, if possible.