hi I have an early 2000s UL. it was serviced two years ago and despite a lot of gigging it still runs strong. one issue though: when I’m at full band volume on high gain mode the red channel is noisy— I get high-pitched squealing / ringing that is different from regular feedback. if I back the gain off to about 9 o’ clock it mitigates, same if I switch to low gain mode. though these are compromises in the sound I want. am I likely dealing with a faulty preamp tube? something else?
Hi @Lucy and welcome to the forum!
Take a look at these videos; they are coming from a power station perspective but are still useful. I’d first see if this is a ground loop.
If you unplug everything from the UL so it’s just guitar in and speaker out (no FX, no pedalboard) do you still get the same feedback?
Also how close to your amp are you standing? Could this be feedback caused by your pickups being too close?
Let’s eliminate these possibilities first.