Say I turn the amp on once every day and leave it on all day.
A lot of this depends on how hard the amp runs the tube. For example, a good 6CG7 usually lasts somewhere around 500 hours (give or take 200), but DNA Starlett rubs the tubes very gently and they can last a very long time
I think it's luck. The power and driver tubes on my EC are still good and were daily driven basically 24/ 7 during pandemic and some long as 2015 ish. They are run at slightly below average operating point per datasheet. One of the rectifiers died while I was listening due to gas leak caused by a glass fracture near the pins ... maybe too much rolling or defect in glass. All I know is I got every last drop from it
I think the answer to that (as well as most questions in life) is it depends. Basically nobody knows. If you don't roll a lot, and turn off the amp if you're not planning to use it for over an hour, you should get some mileage from your tubes. Also, tubes don't really need to warm up too long. @atomicbob did a piece about maximizing warm up time and 10-15 minutes was all it takes to start enjoying your tunes.
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