03-06-2016, 11:52 PM
So i'm stuck with this hum that won't quit. I did a lot of work on my V4 (aluminum knobs version). However the amp does put out some good sounding bass.
So here's what i've done so far :
- Changed every darn cap in the amp including large filter caps with the fliptops kit. (did the V4B coupling cap conversion)
- New JJ's 7027 matched quad
- All resistors seem good
- All tubes seem good, i tried replacements for every single one
- Tried poking around the boards and connections with a wooden stick, nothing happened
- Reheated almost every soldering point
- Deoxited every pot and jack (deoxit fader F5 for pots)
- Grounded AC installed
- Tone PEC 7 pin package replaced with discreet components (eq works fine)
I tried removing tubes (V1 and V2, then V201, then V3) to isolate the hum, but there seems to be hum induced in every stage... The only way that the amp quiets down is when i take out the phase inverter V4 tube. I also noticed that the hum balance pot doesn't change anything at all when i turn it. The post resistance reads good. I also tried changing the case orientation to see variations due to possible outside magentic fields but nothing changes. I tried shorting various points of the signal path to ground and it reduces the hum, with more reduction as i move closer to the power tubes (output of C7, input of C201, output of C10).
any thoughts ?
So here's what i've done so far :
- Changed every darn cap in the amp including large filter caps with the fliptops kit. (did the V4B coupling cap conversion)
- New JJ's 7027 matched quad
- All resistors seem good
- All tubes seem good, i tried replacements for every single one
- Tried poking around the boards and connections with a wooden stick, nothing happened
- Reheated almost every soldering point
- Deoxited every pot and jack (deoxit fader F5 for pots)
- Grounded AC installed
- Tone PEC 7 pin package replaced with discreet components (eq works fine)
I tried removing tubes (V1 and V2, then V201, then V3) to isolate the hum, but there seems to be hum induced in every stage... The only way that the amp quiets down is when i take out the phase inverter V4 tube. I also noticed that the hum balance pot doesn't change anything at all when i turn it. The post resistance reads good. I also tried changing the case orientation to see variations due to possible outside magentic fields but nothing changes. I tried shorting various points of the signal path to ground and it reduces the hum, with more reduction as i move closer to the power tubes (output of C7, input of C201, output of C10).
any thoughts ?