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GA20 is gone microphonic

4/11/1998 10:03 AM
HM GA20 is gone microphonic
The reverb on my amp started going microphonic  
after the amp gets warmed up and the tremolo won't come on at all.  
I have tried switching the tubes but it makes no differance the first channel works normal and thr reverb channel works fine with no reverb.  
I suspected the switch circuit first it rings out good with a meter i resoldered the prongs on the plug.  
After looking at the schematic i pulled the plug out and have the same feedback problem  
the switch assembly must be ok.  
Were can i look next for this oscillation  
The amp has an adjustment off of pin 4 it had a voltage reading close to that stated on the print so i assumed it was ok it looks like pot with the wiper connected to a light bulb or 1 loop inductor labled Z1 on the schematic just wondered what you called it.  
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