So is there a time when you should get your head serviced? I just bought a JCM 2000 DSL Marshall stack. I don't have any problems with it at all but when should I think about re-biasing the tubes or replacing them? Is it something that should be serviced every year or two or do you just keep going until something goes wrong with it? I would hate to be in the middle of a gig and have it freak out on me :P.

Thanks,