2:50/Triaxis feedback issues are back

[7enderbender]

It seems that the feedback issues on my Triaxis/2:50 rack are back. In short, what happens is that on high gain settings the amp occasionally start to squeal even when the guitar is rolled off. Now, the noise gates (266XL) keep it at bay mostly. And it's pronounced when I play with my wireless (Shure QLXD) which leads me to believe that it might be impedance related somehow. It went away in the past and I've toyed around with different error prone parts of the big puzzle (wiring, electrical hookup, ground loops, cables, main tubes etc etc) and never found the source of this.

Two things I want to try next: I'll hook up a second cab - right now I run this rig usually through one Rectocab 2x12 wired in stereo. I've always wondered if the common ground on the cab (??) might be an issue somehow. Unlikely, but who knows.

The other question I have is if anyone ever swapped out the 12AX7 tubes on the inside of the 2:Fifty. Could they ever be microphonic and cause something like this?

As you can see I'm at the moment trying to narrow it down to the power amp section. Obviously, this might was well be an issue with the Triaxis or the DBX noise gate or my G-Force.

Any other suggestions?

 

[user 39402]

When was the last time you retube the unit?

 

[vick1000]

Any tube can become microphnic, and despite what people will tell you, all preamp tubes can cause feedback when microphonic, even phase splitters. So start swapping out preamp tubes in both, with a known good tube, until you find the culrprit. Also a bad pick up in your guitar can cause this as well. Always best to have multiple rigs and guitars for trouble shooting.

 

[7enderbender]

Any tube can become microphnic, and despite what people will tell you, all preamp tubes can cause feedback when microphonic, even phase splitters. So start swapping out preamp tubes in both, with a known good tube, until you find the culrprit. Also a bad pick up in your guitar can cause this as well. Always best to have multiple rigs and guitars for trouble shooting.

Thanks, yes, I'll start doing some testing on the internal tubes. The guitar I have pretty much ruled out since this issue also happens when the guitar is rolled off. Good idea though - I'll double check the guitar I played last time as well making sure there isn't an issue with the pot or switch on that one.