Hello, Lacaca ... welcome to Chordie!
I have a Peavey ValveKing212 which has the same tube setup as yours, and I re-tubed it a couple of years ago. My symptom was a high pitched squeal which would come out the amp once in a while, even though it wasn't very loud. The tech at a local music store suggested some things:
Pre Amp Tubes (6L6's)
- he said that when the pre-amp tubes start to go, there will typically be clicks, squeals, crackling, fuzziness, etc.
- If it's just one bad tube it will usually be glowing less than the good tubes.
- he also said a person can also gently tap each tube one by one, using something that doesn't conduct electricity (like a paint stir stick, plastic utensil, etc.) while the amp is on. A bad tube will react to this in a way which you will hear
I just replaced all 4 of the 6L6's at that time, and the problem was solved.
Power Amp Tubes (12AX7's)
The power tubes (12AX7's) will show trouble by a noticeable drop in power, and usually glow more of a deep red color than usual. If they're really bad, the amp will over-heat, and the on-board fuse will blow. These tend to wear out faster if the player is loading them heavy on the front end, with overdrive pedals, active pickups, etc. Here's a pretty good link that describes these things better than I did ... I hope this all helpful:
http://www.diamondamplification.com/blo … e-problems