Squealing when I turn the gain up

[elwyn]

My qr is squealing when I try to turn the gain up. I've tried all kinds of different tubes in v2 spot but nothing seems to work, I can't turn it past 10 without it squealing really crazy. Have any of you guys ever had this happen? 

[splawndude]

Have you tried the tap test?

Have you tried swapping some of the other preamp tube slots?

Guitar straight into the amp - no pedals anywhere?

Also try it with the guitar plugged into the effects return jack.



(not an EE, just things I would try out of the gate)

[elwyn]

Yeah I've tired just about everything I can think of, I have a nitro too and it does not do this with the same pre amp tubes so I don't know

[gtrjunior]

+1 on the above from Splawndude especially plugging straight in. Eliminate the possibility of you're board or anything you've got in the loop causing it. Disengaged the loop altogether too.
I find that I can turn my QR pretty loud before I get uncontrollable feedback...

[splawndude]

Hey Elwyn


Again, I'm not an EE but these might be some additional steps I'd take in addition to reaching out to Scott or a reputable amp tech.

Sounds like you've done all the basic troubleshooting including the removal of pedals, swapping tubes, swapping guitars and amps. AND you have a Nitro right there to validate all of this stuff.


-spray tube pins with contact cleaner (like Dioxit, not WD40) and work tubes in and out to clean and lubricate sockets
-do the same thing with the guitar insert jack
-do the same with the loop. remove all pedals. also try patching loop with small patch cord, etc
-turn the gain all the way up and put volume all the way down and slowly bring up volume and note where squealing starts
-conversely, turn the volume all the way up (within reason) and bring the gain slowly up until squealing starts
-carefully remove amp chassis and look for cold solder joints, blown resistors, scarring of any kind. DO NOT TOUCH ANYTHING INSIDE
-get a tad of contact cleaner inside the volume pot (ask if that doesn't make sense)
-there are some other things you could do along these lines but you'd have to do it with the chassis out and the power on - which is super dangerous.

So unless you are real comfortable around live circuits like that you may be to a point where it needs professional help. Even an amp that has been turned off and unplugged can be lethally dangerous to touch with your bare hands. The power filter capacitors specifically, but also any trace to and from those caps.


Good luck brother,

[DonaldDemon]

I had this issue for a while and irrc it was the tube sockets that needed to be retensioned. I did it myself but you need to know how to do this safely or you could get fried. It's fairly easy to do. I think if the sockets get loose then the tubes can be vibrating slightly at higher volumes, hence the squeal.

[mikeyboyeee]

Mar 27, 2017 21:34:45 GMT -5 DonaldDemon said:

I had this issue for a while and irrc it was the tube sockets that needed to be retensioned. I did it myself but you need to know how to do this safely or you could get fried. It's fairly easy to do. I think if the sockets get loose then the tubes can be vibrating slightly at higher volumes, hence the squeal.

Can you provide any more detail on how this is done? I have similar issue on my V2 socket.

Thanks

[PDC]

I had this symptom with my 100 watt Nitro. I also swapped in several different pre-amp tubes with modest, but limited improvement. I found that Mesa SPAX-7 with the shrink wrap were noticably quieter than just about any other tube out there. But at the end of the day, I found that when rolling fresh power tubes through the amp, the high end feedback was reduced significantly. Sounds kind of counter-intuitive because we always presume high end squealing is a pre-amp issue, but I had a power tube that was obviously on its way out and made the amp much more sensitive to front end squeal.