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I cannot for the life of me figure out why my amp is producing such a horrible fizzing sound at nearly all levels. Right now im running a single gain stage into a split-load PI into 2x6L6s. Hardly enough to generate distortion, right? I dont have any hum or noise issues. Checked all components out of circuit with a meter. All voltages check out fine. Made sure there were no components shorted to ground. Tried several different speakers. It sounds like a old 8" speaker that has been torn. It sounds like I can hear the correct sounds coming through, but the fizz is so dominant over it. This is annoying.
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Without more info, I'm going with either a parasitic oscillation (related to layout, lead dress or grounding. Or crossover distortion (power tubes are biased waaaay too cool). You should also check the drive on both PI outputs. If only one tube is operating it would sound like you describe. Is this a new build, or was this a working amp that broke?
Chuck"Take two placebos, works twice as well." Enzo
"Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas
"If you're not interested in opinions and the experience of others, why even start a thread?
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Its a new build im working on. Started as a PA head, but I ripped it all out and started over with something else. It is a working design, but Im tweaking it so much that little problems show up.
The bias is fine. Ive installed an adjustable pot so I can meter with. 2x6L6 about 40mA per tube. Yesterday I was having a problem with the heater wires on the second 6L6. This would obviously cause that tube to give out, but I fixed that problem and at the time there were no other issues. I HAVE had about 4, 2' jumper cables at all times redirecting the circuit for testing purposes, so that could possibly present some lead dress issues. I think Im about to rip the whole preamp and PI out and start over.Comment
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similar problem...
with a silvertone 1482. The amp produces its normal tone, but with a layer of fizz on top. Any luck fixing it?Comment
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