Mark V Ch. 1 Feedback Issue

Hey all,

Wondering if anyone has experienced a similar issue before ...

CH. 1 Tweed, Normal Mode, Gain all the way up, with or without any input signal being applied.
When sweeping the mid knob the amp self-oscillates through a certain range.
Overall volume is set low, FX loop on/off makes no difference.

I took it into service, they checked tubes, cleaned the pots and said it was fixed ... took it home, same issue.
I spoke to Mesa service twice and they said it's either tubes (which were swapped and checked) or lead dress on the pot.

I'm going to take it back to service to replace the pot and see if that fixes it. Amp is still under warranty.

Here's the video of the issue, it's pretty self-explanatory:

https://youtu.be/vdqWVDxM8QQ

Cheers, I.

Strange one that, I've had microphones tubes show up in V1 with high gain settings and volume but that's always been at a lower pitch than your issue. Probably rule out the tubes, leaky capacitor in the tweed circuit maybe Letting DC onto the middle pot somehow?

You may want to share the video with the Mesa tech. You can always send a link to this post if it makes it easier to do so.
Interesting.... no clue on what the issue is.

Thanks for replies, I already sent the video to Mesa and the second time I spoke with them, they mentioned it may be lead dress from the pot.
Amp is going back to service today and hopefully they can re-pot. My first thought was a leaky cap in the circuit but Mesa tech said no.