Help with weird noise -2203

[The Dude]

Agree. That is why I asked what he did. I suspected what followed. "......holy shit is this loud!!" was a clue.

[Jonsnothere]

Enzo, that’s right but I think I need some additional rewiring, when I flipped the pin 3 wires and put the presence wire back on 4Ohms it was a massive loud hum again.
Curious on the direction of those wires, in the diagram they are fed through the middle then one left and the other right (blue to tube 2, then 1, red to 3 then 4) where my OT is on the far side so they are wired from right to left (blue to 2 then 1 and red 4 then 3)
Before redoing this, could that be the issue? These aren’t emitter wires so that direction shouldn’t matter but I may be wrong in this

[Jonsnothere]

I lifted the presence NFB/wire again and just noticed that the volume is wide open, dial does nothing but the master still works fine but it’s like loud at 0.5 on the dial, like instant loud, it’s an alpha pot but that’s quite exponential

[Helmholtz]

Curious on the direction of those wires, in the diagram they are fed through the middle then one left and the other right (blue to tube 2, then 1, red to 3 then 4) where my OT is on the far side so they are wired from right to left (blue to 2 then 1 and red 4 then 3)
Before redoing this, could that be the issue? These aren’t emitter wires so that direction shouldn’t matter but I may be wrong in this

Not clear. If your layout is different, please post picture.

[Jonsnothere]

"in the diagram they are fed through the middle then one left and the other right (blue to tube 2, then 1, red to 3 then 4) where my OT is on the far side so they are wired from right to left (blue to 2 then 1 and red 4 then 3)"

Image shows sockets in reference to previous note, left-right tubes as 1,2,3,4. Red wire goes to socket 4 then to 3, Blue goes to socket socket 2 then to socket 1. This isn't final image, the board and some wires have been removed.

[The Dude]

Did you switch the red and blue OT wires? If disconnecting NFB got rid of the oscillation, that's what you need to do. If they are reversed and phase is wrong, you'll get positive feedback instead of negative feedback, which turns the amp into a big oscillator.

[Chuck H]

And if swapping the pin 3 wires produced hum that wasn't there before I think it's possible an error in the wiring occurred at the same time. Maybe changing too many things at once with the NFB lead ohm tap and presence control. It's impossible to isolate the new hum to the pin 3 swap now. Recheck your wiring. Especially with respect to ground connections for the PI and presence controls. If you don't find an error, check it again.

[Jonsnothere]

Thanks Dude/Chuck,

You are both sorta correct, it was a directional wiring on pin 3, as the cycle of wiring is important for those a simple move of the red wire to tube 3 resolved the issue. Presence knob is functional again.

Still have a few issues but as the original post was about the hum I’ll consider this closed and then start a fresh thread as that I believe is a separate issue, also I want to rule out any of my own potential errors and make a video demo, no time as I’ve been travelling but thanks again for the help, greatly appreciated!!

[Chuck H]

Still have a few issues but as the original post was about the hum I’ll consider this closed and then start a fresh thread as that I believe is a separate issue,..