Why aren't new vacuum tubes as good as old ones?

I wonder which the world will run out of sooner, good high quality NOS tubes that are years old or oil?

I hope the suppliers of modern tube technology get their act together sooner and better than those making the new vinyl seem to be doing.

I have to believe though that the ability to make good tubes cost effectively still exists, even if it might not occur that often in practice.

I have no clue really. Too few data points with the tubes I have used personally in recent years. Overall, they seem to do the job well, though getting very quiet ones suitable for use in a phono pre-amp seems to cost a premium.

Definitely a good idea to buy from a reputable source that has the ability to accurately measure and rate each tube. I would expect that at a minimum in general, unless attempting to buy on the cheap, which will surely be more hit or miss in general.

I have no clue but based on what I know from what I hear I am with the wolfman on this. New tu.bes are not all gloom and doom like most new things are often regarded to be by audiophiles. I'm sureI can guess which side the sellers of expensive NOS tubes are on.

More audio twilight zone rumor accepted as fact.

Or, show us the facts to back up the assertion?

On off generalized observations have some value but clearly do not tell the whole story.