Tube life

I fall asleep to music; wake in the morning and flip the amp off. So I have two questions:

(1) I’m guessing my amp thus stays on 50 or so extra hours a week with no signal. Does this have any significant effect on tube life? (EL84s). (I normally replace them every 2-3 years; if after a week or so, I am not aware of any difference, I put the old ones back in, wait year or so and try again.)

(2) what obvious signs are there that tubes need replacement? (other than the method noted above, the growing urge to replace them for the helluvit, or, say, the time one of them spectacularly burst into flame around 1AM; [that was AWESOME! ] Turned out to be poor pin connections, which had been showing signs of that for months; can’t remember whether the tube survived. The amp is still going strong.)

Thanks.