I am working on converting a filmosound projector amp to a guitar amp. So far I have removed the oscillator circuit and the negative feedback circuit, in large part to make room in the chassis.
When I turn the volume pot past three quarters a crazy static type distortion/feedback type sound occurs, but not squealing. This phenomenon existed before I removed the negative feedback loop.
I have tried the following to remedy this situation:
Bad pot? I replaced the pot with a new 500K pot. No change.
Pot value too large? Original pot is supposed to be 500k but is really closer to 350k. I reduced the value to 300k with a resistor. No change.
Bad preamp tube? Tried a different 6SL7. No change.
Layout? Tried moving wires. No change.
Also changed wire to grid to a shielded cable. No change.
Any ideas on what might be causing this effect? Another post had a similar question about a filmosound, but the i don't believe the problem was ever solved.
I have only been working on tube amps for about a year, so my knowledge is pretty limited. Any ideas are greatly appreciated, no matter how obvious they may seem to the more educated.
Also, any other potential changes the anyone notices, that would be an improvement, I'd like to hear about.
thanks in advance.
here's the link to the schematic:
http://s294.photobucket.com/albums/m...oundL-1Mod.jpg
When I turn the volume pot past three quarters a crazy static type distortion/feedback type sound occurs, but not squealing. This phenomenon existed before I removed the negative feedback loop.
I have tried the following to remedy this situation:
Bad pot? I replaced the pot with a new 500K pot. No change.
Pot value too large? Original pot is supposed to be 500k but is really closer to 350k. I reduced the value to 300k with a resistor. No change.
Bad preamp tube? Tried a different 6SL7. No change.
Layout? Tried moving wires. No change.
Also changed wire to grid to a shielded cable. No change.
Any ideas on what might be causing this effect? Another post had a similar question about a filmosound, but the i don't believe the problem was ever solved.
I have only been working on tube amps for about a year, so my knowledge is pretty limited. Any ideas are greatly appreciated, no matter how obvious they may seem to the more educated.
Also, any other potential changes the anyone notices, that would be an improvement, I'd like to hear about.
thanks in advance.
here's the link to the schematic:
http://s294.photobucket.com/albums/m...oundL-1Mod.jpg
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