Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Platefire on May 28, 2011, 11:29:08 pm
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At first it was frying eggs. I tested all the 12Ax pre's and ended up replacing V1 with new and got rid of the frying. The amp sounds great but when I play a note I get some low level static that travels with the note and dies with the note. Just guessing what to tackle next, I was wondering if the static with the note could be due to leaking coupeling cap? Any suggestions! Platefire
FYI--I checked all the other exterior stuff first like different guitars, different speaker, different cord and it didn't make any difference.
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Might be parasitic oscillation. Is there negative feedback? Have you swapped speakers?
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The "frying eggs" sound is usually the 100K plate resistors. Since the new tube seems to have fixed that, I'm not sure, but resistors are cheap. Wouldn't cost much to try. jjasilli's parasitic oscillation idea is worth checking, also. I just retubed my son's amp. When the hot switch was engaged, it would squeal. It never did that before. Turns out, the new tubes (Tung Sol) have a bit more gain the the old ones (EH). I used the chopstick method and found a wire from the tube to the relay that made the squeal come and go as I moved it around. Replaced it with a shielded cable, grounded at one end, and all is well. Since it's just making noises when played, you may need a second pair off hands to help with this test, always a pain.
Good luck,
Dave
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Thanks! Another thing I noticed last night is that it don't do it until it gets good and warmed up. Got a lot of stuff going on right now, so I'm not going to tear it down right now. Just getting some ideas of what to check when I do. It's one fine amp and I want to keep it on top shelf. Platefire
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Bad tube/Bad plate resistor. Just did one of those.
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So you were working on an Accomplice?
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Just wanted to say it was the V1 preamp tube and V4 PI tube causing the racket. I changed V1 and it got more intermitent after that and didn't get rid of it completly until I changed out the PI tube. I've had it in my jam room steady playing over it the last two weeks and it's been running perfect--so I put the back plate back on it tonight and call it fixed. Thanks, Platefire