A faulty design can ruin a tube and blow a fuse .in earlier days some of the less expensive Chinese integrated amps,power amps are horribly designed. Unless it us a well respected brand like Jolida they are night and day better then even 5 years ago for example. If you sell tubes you should give readings for matched tubes under load with each pair. Brent Jesse recordings does, Andy at Vintage tube services for years has Allways inspected under load . With expensive tubes you just cannot afford to just exchange on a $300 pr of rare tubes.
If tubes test as N.O.S , failure not likely do yo the tube .the amp voltage regulation
Drifting or weak is very possible as just one possibility .I am referring to small signal tubes. Power tubes are another animal but still a strong N.O.S pr of power tubes if biased properly should last for at least several 1,000 hours
If tubes test as N.O.S , failure not likely do yo the tube .the amp voltage regulation
Drifting or weak is very possible as just one possibility .I am referring to small signal tubes. Power tubes are another animal but still a strong N.O.S pr of power tubes if biased properly should last for at least several 1,000 hours