Let's say I play for 30-45 mins, every second or third day. How long do you think my tubes will last?
You won't have to replace them for a couple years if you play at that rate.

*Edit: It also depends on how loud you play. If you have the amp cranked then the tubes will wear out faster than they would if you were playing at whisper volumes.
okay, thanks. The reason is I'm considering whether or not to buy a tube amp, and the price of replacing tubes, and how often you have to do it is a determining factor.