KT120 longevity

Yea Wolf, just keep an eye on those electrons and you'll know when to take action. Those little buggers will start acting up and start hissing and whining and moaning under their breath. After that they will quickly turn into arsonists. I think those electrons are what the communists sent over here to keep a spying eye on us, so don't let 'em get away with anything evil.

I've read 5000 hours.

I guess you will be the standard case to model future behavior on.

Tube amplifier manufacturers typically specify 2000 hours as the useful lifetime of these power tubes. It doesn't mean they suddenly drop dead after that, but performance degrades with more time.

FWIW, I drive my ARC VS-115 with KT-120s. ARC still recommends replacement at 2000 hours. Do they have a longer life? Dunno. Maybe yes if you drive the tubes with quality electrons. I'd call the factory and ask the techies.

Thanks for nothing my fellow tubeheads. I'm aware of Tube Death Theory but still wonder how long this particular tube type can continue before becoming land fill. Mine are still seemingly in the 4,750 hour break-in period. They're boring me with their longevity...they have lost nothing so I can't justify replacing them with new KT120 Cryoed Super Platinum Matched Quad ARC Factory Mermaid Drool Glass Polish Lubed Gold Pin Blessed by a Pope Hand Rolled Asteroid Mica Spacered Vintage Vacuum Sucked versions...thus robbing me, that's right, ME, of the simple guilty pleasure of tube rolling. Come on KT120s! Die bastards!...DIE!

Wolf, given your vast guitar amplification etc experiences, you should have a decent idea concerning tube life. Are you referring to the particular application of your Jolida amplifier? Or are you just bored and being indecent?
I'm all for that, btw

I've been using an octet of KT-120s for about the same length of time in a pair of Rogue M-180s. I use the amps for much of the day nearly every day. No issues so far. I previously blew 3 KT-90s (along with their fuses) in the same amps. This reminds me that I should probably order some backups, though.

Isochronism...I rarely changed guitar amp tubes. Unless something started sounding strange or blew up (VERY rare) I blasted through various Twin Reverbs, my white Bandmaster head, and whatever Boogie/Marshall/Hiwatt I had. Maybe because I couldn't SEE the tubes or something I just forgot about them. I assume some guitar players back then cared about such things like I do now, but there seemed to be 2 tube types: New ones and the old tubes you almost never replaced...now with my groovy "boutique" little tube guitar amps I get the urge to roll tubes in them out of curiosity, like an idiot. I think I was better off not giving a crap.