Power Tube Troubles/Mids??????

[slayer]

OK, I have a Peavey Ultra 60 1x12 and sounds awsome through my 4x12 and all, and never use Mids, I live that on "0" all the time. I use JJ 6L6`s and never have trouble with them, except when I turn the mids on, the tubes turn bright blue and the louder I turn it up(mids and volume), the bluer they get and the sound starts going up and down. Turn the mids off and it all goes back to normal, no blue and the sound is perfect. This is the 2nd time I have noticed this and actually blew a fuse once when the mids were on. If the mids are off, everything is perfect. Now this amp has active controls, could there be something wrong with the mids knob(the mids knob is a master mids for the Crunch and Ultra channels. This is super wierd, any ideas why? Oh, and 1 of the power tubes out of 2 is way more blue than the other. Could this be a sign that they are going? Quite strange the Mids is the only thing this does this with. Thanks-Jack.

[Misanthrope189]

That's very strange...tubes don't normally glow blue, do they?

[slayer]

Good question!! I think they may when they are starting to go bad, but this is only the case when the mids are on and the more on the mids are the bluer the tubes-crazy Jack.