Presence control causing high pitch oscillation question

[jackplug1]

The presence control causes high pitch oscillation at low settings in my Seplex build.
It disappears at higher settings so long as the MV is not too high
I does not appear to be affected anything before v2b
I have researched this but this fault seems to relate to push pull amplifiers and is to
do with postive feedback and reversing the opt secondary leads.
The NFB wire is screened and I have moved the presence control wires away from the
tone stack
The fault is not present if the NFB wire is disconnected.
Also the presence control has no effect on the tone

Should I replace the nfb resistor with a different value ?

BTW I am using a 6v6gt with the appropriate cathode components

There is no mention of this problem here:
https://chasingtone.com/the-seplex/

[pdf64]

Have you tried flipping the polarity of either the primary or secondary OT windings?

Maybe presence will work after that. If not, please provide well lit, in focus photos of your build.

[sluckey]

The fault is not present if the NFB wire is disconnected.

Swap the two OT primary wires.

[PRR]

> oscillation at low settings

"at low settings", the Presence is doing nothing.

Let's check. Disconnect it.

I am thinking the power amp is just unstable, but moderated by turning-down the Master. Showing that the Presence is just a side-track.

And what they said. Pictures! And swap leads.

[jackplug1]

I tried swopping the secondary wires before but that made no difference so I put them back to what they were.
Following the advice I reversed the primary ones and the fault disappeared, so thank you!
I think I have noticed that the amplifier sounds a lot more healthier, or is that my imagination?
I don't know what the explanation is for the fault which was corrected though.