I built a Champ (based on the STF electronics super charged amp - I have built two of these and they work great) and when I turn the Master Volume past a certain point I get some pretty bad oscillation. As I turn the MV up the oscillation frequency goes down... here's the weird part - (I know this is a no-no but only did it for troubleshooting purposes) when I remove the speaker cable it is the 12ax7 that is mechanically oscillating - I can still hear the oscillation only it is not amplified through the speaker... I have tried a new socket, different tubes, new MV pot, moved leads around with no luck. Any ideas on where to go from here. What voltage measurements would be relevant in this situation - I will gladly post them. Help is much appreciated...
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Champ preamp tube oscillates
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After further investigation I think it is actually the OT that is whining / oscillating. With this in mind I took a shot in the dark and removed the (what I believe is the negative feedback) lead from the 1.5k resistor (R10) 22k (Rf) resistor to the output jack and the whining disappeared. What does this tell me?
guitician: are we talking about the same thing? Positive feedback / negative feedback... what would I "check" with the power caps?
edit: I forgot in my first post - the schematic
http://i27.photobucket.com/albums/c1...turboChamp.jpgLast edited by captntasty; 05-29-2009, 07:50 PM.
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