How often should I change my tubes?

This will depend on how often and how hard the amp is played.  Power tubes will be replaced more often than preamp tubes. Frequent use may require the power tubes to be replaced every two years, and preamp tubes  about every four years. You may not notice gradual changes in the sound over time from tubes wearing out. A fresh set of tubes usually brings an amp back to life when you start noticing the amp doesn’t sound quite right or it seems something has changed.