My amp is squealing, cutting in/out..what's wrong?

[FireBottle]

After turning it on and warming up the tubes, my Soldano Astroverb combo starts to hiss quietly, then whistle, then squeal, then - crack-pop - quiet again...sounds pretty scary. It did this a few days ago and the fuse blew, so I changed it out. Now it's doing it again - more even. I looked at the tubes and it seems one of the EL84's is burning brighter than the other (probably not good, eh?). I'm hoping it's just a tube change (haven't been changed in a couple years) so I ordered a couple of Ei EL84's...but could it be something more, uh, complicated? I don't have a local tech in Chicago (the guy I trust is sort of a long way from me) so I'm hoping it's simple and thought that the symptoms I'm describing are familar to some TGP'ers.

Thanks!

[phsyconoodler]

Try a set of tubes first and see what happens.hopefully it didn't take out a screen resistor.

[Suproman77]

A simple tube change should solve this problem. If not, let us know if something has changed as a result.

[FireBottle]

Thanks for the advice...I can only sit and wait for the tubes to get here...