Severe oscillation issues with NFB circuit

[kka]

Hello folks,

I need some help. I am working on a Cameron Old Bitch. I replaced the PT first (Mercury), tested amp afterwards and all is well. Then I replaced the OT (Mercury), tested the amp afterwards and all is well. Then I see that the ground wire of the bias circuit's filter caps (see photo) became detached. It looked worn out, so I replaced the wire (gray) and connected it to ground (back of tone pots).
Turned amp back on and had very loud oscillation, frequencies from deep motorboating to HF squeal depending on how the Presence and Depth pots are turned. When I disconnect the purple NFB wire (connected to 8Ohm jack) there is NO oscillation and amp works fine, of course without presence and depth controls working.

I tried to trouble shoot this issue and am not getting anywhere. I even temp. hooked up the old OT and with that attached it oscillates the same.

The oscillations happens with or without signal going into amp.

Any help is greatly appreciated. Thanks !

[g1]

Reverse the OT connections at the power tube sockets.
When you put back the original OT are you positive the same 2 wires went to the same 2 power tube sockets?

[kka]

Reverse the OT connections at the power tube sockets.
When you put back the original OT are you positive the same 2 wires went to the same 2 power tube sockets?

Yes, I mixed up the 2 OT wires ! Didn't think of it at all and looked everywhere else inspite of it not making any sense. Thank you !