It's a carvin Legacy 3 , cable and guitars are fine. I'll play and hear the thundery sound of each note, and then it'll dull, and then it'll make pop noises, it will get louder, and then the sound is so dull it sounds clean but notes sustain for half a second.I blew a 12ax7 a couple months ago and replaced it with a groove tube. All the others were fine, but some sort of off brand. The EL34 glow nice and bright, so I doubt it's those. I had to replace another, but the only ones the local stores sold were mesaboogie, so I took one. After I put it in, another started to look dim, and it still didn't work. Should the brand match or something? Does anybody have an idea as to what is wrong? Thank you in advance.
replace them all if you never have.

JJ Ecc83 or JJ EC803 would be a good choice for the preamp and the JJ E34L for the power section

Just because a tube glows doesn't mean anything
I had a similar problem happen with my Avatar head. If you played a loud power chord, it would starting cutting on and off like a killswitch, and popping. Oddly enough clean and low volumes still worked. Had to send it back to the amp maker twice actually for the same problem. He said it was loose wiring.
Well, tube glowing means there is some sort of signal going through it. It also means that it is not not glowing, which means that there is something wrong in the signal before or in the tube. I'd like to keep the same tubes. I have never replaced all of them, but I bought this used with new tubes so I never decided to replace the tubes (other than the pre-amp ones that went out). I think I'll see what GC does about it, I have a 2 year warranty that was supposed to include new tubes (added on to the deal, it wasn't traditional) and traditionally on the deal is to get free repairs on everything but tubes. I took it back and they did nothing but say to have someone check it out, which is what I as doing. I guess I spent like 100 dollars on nothing, so I'll complain and see what they do. Thanks!
Tubes are only covered for 90 days. You will have to breakdown and buy some new ones.