power tube replacement in spider valve mkii 1x12... best tubes for the job??

[BBMOORE]

I absolutely love the amp. And it doesn't surprise me that I'm replacing the power tubes after only having it a few months, due to the fact that the amp has probably been turned on more than it has been turned off, since I brought it home. I've always been a tube amp aholic, but never had one that I just couldn't stand to turn off and walk away from.! Anyway, any advice on the matter would be greatly appreciated!