Re: Valve
I'm sure some will disagree, everyone has their own ideas about when to replace tubes, but in my experience power tubes either work or they don't. You can change them every year or every two years or whatever if you want. All of the tubes in my amps are used, perfectly good tubes that somebody had taken out and replaced as routine maintainance then tested and recycled through my tech to me. Preamp tubes can go bad and cause humming, whistling, and other noises. You can tap on the preamp tubes to check them, if there's noise when you tap them that means it's microphonic. That's not necessarily a problem in every position, but you don't want a microphonic tube in the actual preamp positions, V1 and/or V2 on most amps.
