So here's the situation. I have been gassing for a new Ampeg B-15N since they were released in 2012/2013. The amp will be for recording / home studio use only. Normal use will be about 1-3 hours a day, 5 days a week. I usually play for an hour, collect my thoughts for an hour or so then play for another 2 hours. It will be in standby during the in-between time. I know there is no way to determine how long tubes will last. Under the conditions above, how long should they last? And, how much does it cost to have them replaced, including cost of tubes and tech time? Thanks in advance. Any info and experiences are appreciated.