I did a bit of searching on when you need to replace pre-amp tubes and have found that you do not need to replace them unless they are going bad. Loosing gain, microphonic. So my question is, basically how does this sound. Loosing gain I understand, and the term microphonic to me means the same thing or maybe a small sound with no bottom, also, how does it occur. Is it gradual over time or can it happen suddenly. The reason I ask is I took my rig out of storage and set it up at a rehearsal space me and my brother (a drummer) rented. When playing I would suddenly loose volume, down to about half I suspect and then it would come back. It happened a few times. My first thoughts was a bad instrument cord but wiggling it around did not cause the problem, I did not have a spare with me. So right now a dying tube is just a thought, I have used this set up for a few years (5?) when gigging regularly, two to four nights a week. So the problem I have, could it be a tube? If not, what are the characteristics of a dying pre-amp tube? Thanks, Matt.