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

I use new JJ EL84s (7189s) in my Burriss Royal Bluesman amp, and they sound great.

Here's an interesting tidbit from the Atma-Sphere FAQ page:

"Atma-Sphere equipment is designed to work with commonly available tubes, making our products easy to live with. The 6SN7 tubes we use are produced in China but there are many aftermarket versions available. The output tubes are Sovtek, Svetlana or Chinese. The miniature triodes used in the preamps such as the 12AT7 and the 12AU7 are usually Chinese. Other types of tubes may be available on request."

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.

While it's certainly possible to have an individual craftsman make an audio vacuum tube, the tubes from the golden age of tubes were made in highly automated factories that practiced tight quality control.

The Blackburn Factory

Thanks Wolf except MY experience has not been as good, at least the last two times out. I sure hope the third time is the charm. This time I purchased the one year warranty for an additional 20% of the tube price. The last two pair didn't last beyond 3 months, 6SN7 in a pre output stage. Maybe an unusual experience, or something wrong with my preamp, for sure not the latter, the problem is tube quality.

I test ALL tubes I purchase prior to installation and keep a log of the dates installed. In the case of the first two sets, when I noticed noise I checked them out and the transconductance had gone South considerably, not a short, the tubes just didn't hold up, one was marginal the other tested weak and replace. The manufacturer sent me another pair. These lasted a bit longer, 5 months but certainly no more than 1500-1800 hours and I'm being generous. When I installed the most recent tubes a few days ago I tested the old stock Sylvanias I had in the pre-amp that were installed a little over a year ago to replace the failed tubes. They tested stronger than than the new tubes I just purchased and the same as the day I installed them. Unfortunately these very nice Sylvanias don't come close to the sound of the Chinese tubes, it ain't a subtle difference for sure. For 250.00 is it unreasonable to expect at least 4K hours of life or more? Or is this the new normal or is my experience unusual?