i think if they past 10 hours mark, they are reliable ( they survive )..all of them they have more 10 hours on them, all night long, and day , wonderful sound...
Today i have read some posts "they have bad reputation".. but the people put them in guitar "combos", to play loud and distort needs to much current... i believe.They didn't handle more current as they specs, but in a stable class A Amp made with specs for and biased for a el34 "hot side" no more 25W each, they play wonderfully, in direct comparative with Philips more bass, and medium but the highs are almost ...
They have born only for home HiFi...Please guitar players this is not your tube..