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Ampeg V4 problems...?

3/29/2004 7:03 PM
Ampeg V4 problems...?
I'm stumped...and I need some help. I'm not an amp tech, but I want to try and solve this thing...  
My friend's V4 stopped working...low, distorted output and a very loud hum, present with or without guitar input and independent of amp volume control settings.  
I checked the voltages (all ok), retensioned the tube sockets, replaced all tubes (they were originals) with known good tubes, tested the filter caps (all stored charge from 9V battery), checked all resistors (replaced one open resistor), replaced the bias circuit diode and replaced the 2 leaky bias caps.  
It still hums (but not as much), and the output is still very low (non-distorted, but still low). Also, another problem is that cranking the midrange control puts out a VERY LOUD howl. Could this pot have gone bad, or is this normal?  
Anyway, I'm not sure what to check next...I sincerely appreciate any advice you can give. Thanks.  

aris Here's a thought...the amp has 2 ja... -- 3/29/2004 10:38 PM