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ampage archive
Vintage threads from the first ten years
| previous: John Stokes Re: Peculiar Fender Driver Problem... -- 6/2/2000 5:13 PM |  |
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Re: Peculiar Fender Driver Problem/Fixed !
 6/4/2000 3:43 PM |
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andyfuchs | Re: Peculiar Fender Driver Problem/Fixed ! This problem bugged me, and although the fix worked, I couldn't understand why the circuit wouldn't run stable as built. I later found a key difference between an amp that worked, and the one with the problem. I had added a small circuit card, (with separate bias pots per tube )to replace the single Fender pot. The working amp had this board right next-to the coupling caps. The other had it a little farther away (closer to the p-former). The length of the leads from the board to the output tubes was the source of the instability ! The board has a top and bottom resistor (with the pots in between) and the bias 'feed' resistor, along with a small electrolytic from the wiper to ground. Moving the bias resistors back to the coupling cap location (and eliminating all the extra wiring with audio on it) cleaned things right up ! So obvious, yet so elusive.... |
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| Steve Ahola Andy: R.G. I think you just led us to a new wi... -- 6/5/2000 3:31 AM |