Well, my ears have certainly had enough. Aside from my less than mediocre playing, I have decided its time to change the tubes. How do I know? Here are some signs that your tubes have crapped out:
1. The amp is way too harsh on the ears
2. The bass is no where to be found
3. It's all mids, all the time
4. The clean sounds like the dirty channel, and the dirty sounds like rubbish
5. The reverb does not work
6. Your amps' levels are down significantly
7. Any EQ adjustment shows little improvement in the sound
8. You hear a hissing noise (usually a preamp tube)
9. You hear a rattling sound (could be a loose component in a power or rectifier tube)
10. Humming (unmatched power tubes).
When you start to notice a few things that go sour, keep playing around with your amp for another week or two. Switch preamp tubes around to see if you can find the bad tube. I noticed that my cleans became dirty about a month ago, however I played around with different guitars (Gibson SG, strat, tele), and played with different pedals. I was getting a better sound out of the SG, while the amp sounded way to bright and sharp for the strat and the tele. Finally, about a week ago, the amp just sounds like arse.
I beat the hell out of this thing.
I have easily put 10 hours a week on this baby for almost a year and a half straight.
Remember, the first step to the road of tube recovery is recognizing you have a problem :)