Good question. Has anybody here on this forum experienced a 2A3 death from old age?
I've had the old Chinese biplate 2A3s - the ones from 15+ years ago - go south on me, usually around 1000 hours. They would get some brown stain on the glass, like someone was smoking unfiltered cigarettes inside the tube, then they would start to make pops and crackling noises at increasingly frequent intervals. I never saw one just lose emission, which ought to be the normal death as the cathode wears out. And I've seen or heard of a few individual tubes with heat-warped grids shorting out, or transient arcing cathode damage. I can't recall any other experience.
Western Electric used to spec 20000 hours for their 300B, IIRC. That's probably the upper limit of lifetime at anywhere close to maximum specified plate dissipation. Small-signal tubes operated far below spec can last for an amazingly long time if they are well made, maybe 100,000 hours.
I would hope for 5000 to 10000 hours from a quality new production 2A3 or 300B, once the production line has been sorted out. Maybe more from the best, most serious producers. But we all roll tubes so often that it's hard t find a tube that has sat in an amp long enough to fail from pure age.
If you find they are failing too frequently, you can look for some of the 2.5-v 300B clones, sometimes sold as super-2A3s with 40-watt dissipation ratings. In a 2A3 amp they should last a very long time dissipating 15 watts.
