Why do old tubes sound better than current tubes?

Rate of production, American, German, British manufacturers (old tubes)
Modern tubes are just Eastern factory tubes of respective countries but widened production, modern tubes made in former Soviet Bloc and China (because they were behind the curve, and still HAD factories making tubes left.)
The old tubes were made in 'Western countries' and a LOT were made. The vast majority of 'wanted' old tubes were made in England, America, Germany, Holland.
The Soviet bloc was making tubes then too, no one wanted those tubes.
The 'old factories' that made tubes in Western countries are all gone, the machinery is gone.
The factories that made tubes in the Soviet bloc countries is still there. So are Chinas tube making facilities.
That is the ONLY reason tubes are all made in those countries today for sale in the West.
Of any place, I would say China is the most likely to be capable of producing tubes equal or better than the 'old' tubes of the West. But then you have to sort through the junk to find the gold.
The current tube makers may be trying to improve thier tubes, but they are not the same as those old tubes, which hold nostalgia as well as a signal.

I think the tide is turning a little. The Genelex/Gold Lion reissues (Russian), for instance, are gaining real respect. I've personally replaced "Holy Grail" Mullard xf1 EL34s with Genelex KT77s because the new tubes sound quite a bit better in my amps. And the Sovtec 12AX7LPS is a winner. The reputation of many of the old tubes is, IMHO, a combination of performance and mystique/nostalgia. We're paying a lot for the latter.

I also believe the tide has turned in favor of the new tubes. You can get on the boards and read all you want about the "Holy Grail" tubes of yesteryear but I gotta tell ya, many of the new tubes are simply fantastic. I'll be reporting on this subject in TAS and on the AVGuide site. Frankly, it's great news and we all win.

Peter Breuninger
Sr. Writer, The Absolute Sound

The secret is inside. Quality of wire, cathodes, plates, durability...
Low noise (ask Aesthetix Callisto owners, they can tell you something about that), low microphonics, maybe shock resistance and so on.
forget the pricing for NOS, turn back the time 50 years and try to imagine you have in your left hand a Telefunken, Made in Germany and in your other other hand you have a modern Sovtec, Made in Russia, China or in other dark countries.
Do you really think they are equal? :-)
I know the answer. :-)

But we can't make money with old tubes, so let's be happy what is available today. It isn't that bad.
But not equal. I tried some modern tubes, great for the money, no doubt, but fantastic?
Fantastic is something different. But it depends on the quality of the System to hear these differences. I hate the NOS prices, I also bought a set of modern ones too with them to compare. I got my result.