I have an HFMA1 amplifier that has just been completely rebuilt, all caps changed and resistors checked. Tubes are all verified good. Problem: As I slowly bring up voltage I start to hear the signal but if I bring it up any more than about 70-80 volts on the mains it begins to make a crackling sound and the current runs away. I have it connected to an amp meter and shut it down when it starts quickly climbing past 2 amps and crackling. Now, through troubleshooting I have found that it still happens with only the 5U4 installed in the amp. I’m thinking it has to be one of the transformers breaking down at higher voltages BUT I am getting proper voltages from the power transformer and preliminary primary resistance measurements indicated the output transformer is not shorted. Need some opinions from the wisdom in this group. Any thoughts on which it might be or perhaps some other opinions? Thanks as always,
Mauro Mississauga, Ontario, Canada
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