OK... So I've had my Zen Triode on at least 12 hrs. a day, every day, since early Sept. 2012... I figure a total of about 4000 hrs., since some days I had it on 16 hrs. I can't imagine a more rigorous test for these tubes, since I also turned them off when I went to bed...

I popped in a new set [exactly same], and I did notice a certain lift in the definition... So I'm guessing that the 5000 hr. limit is practical.

Note: OK, so you now know that I'm a recluse... (m.)