I've had the newer WE 300B tubes for a couple of years now and they work and sound amazing; no problems at all, and would buy again in a heartbeat. The warranty on these tubes is 5 years, provided you sent in the warranty card when you got the tubes.
Western Electric 300B problem
So I recently purchased pair of WE300B, Friday night first listen. At start up heard mechanical pinging and popping, pre muted so nothing through speakers, after the pinging and popping ended, pre out of mute heard nothing unusual through speakers. No issues other than blue glow at tops of tube throughout 5 hour listening session. Tonight I power up tubes for second listen, immediately see left monoblock tube goes completely cloudy with blue fog throughout tube, this along with popping, right monoblock tube fine.
So it seems I have gassy tube, lost vacuum already! And here I thought recent improvements with quality control there had solved these issues. Not happy with this purchase, been running Psvane Acme 300B's for nearly 1000 hours with no issues.