Hello everybody!
I'm reparing a Super Bass amp and am stuck with a weird problem at the moment. I've replaced all electrolytes in the amp and also had to put in one new tube socket as the original showed signs of arcing in the past (the pcb has lotsa burn marks also).
Now, the amp is ok when idling (power stage bias at around 72mA@450V per side), voltages look good everything seems fine, but when driving signal in, the power tubes start to get hotter and eventually red plate. Also, the negative biasV starts to go down, from about -40V to -60V.
When scoping, the signal looks good all the way to power tube grids, but looks very exploded on the anodes. Sounds and smells terrible. The third set of tubes (used but in known good condition) on trial, so that should be eliminated already... Gone through some solder joints already, but going to double check some.
Any ideas appreciated, thank you in advance!
-Tommi
I'm reparing a Super Bass amp and am stuck with a weird problem at the moment. I've replaced all electrolytes in the amp and also had to put in one new tube socket as the original showed signs of arcing in the past (the pcb has lotsa burn marks also).
Now, the amp is ok when idling (power stage bias at around 72mA@450V per side), voltages look good everything seems fine, but when driving signal in, the power tubes start to get hotter and eventually red plate. Also, the negative biasV starts to go down, from about -40V to -60V.
When scoping, the signal looks good all the way to power tube grids, but looks very exploded on the anodes. Sounds and smells terrible. The third set of tubes (used but in known good condition) on trial, so that should be eliminated already... Gone through some solder joints already, but going to double check some.
Any ideas appreciated, thank you in advance!
-Tommi
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