Squealing amp

[newguitarsmell]

I have had a little point-to-point wired boutique amp for awhile. It is very cool in that is can use a variety of tubes. No, I do not have a schematic ...
I recently swapped out the 6188 tube for another and now it squeals when I first turn it on. I changed all the tubes and it is a little better - as I turn the volume up the squeal disappears.
I can't get the case open to take gut shots.
 

Is it worth drilling out the screws to get it open? What causes that squeal?

[Slimtim]

yeah if you want to fix it you gotta open it up unless it is a tube.why can't the screws be unscrewed?

[newguitarsmell]

A couple are pretty tight but I can try harder. I'm afraid they might strip.

[sluckey]

Put the old tubes back in it.

[John]

Put the old tubes back in it.

What he said, especially the one you swapped out first. I love those 6SL7 (6881) but they can be quite noisy, and make all kinds of weird sounds. I have a few that after 5 mins of playing start to make a whistling sound. The damping rings help. Or just putting in a quiet one ;)