Why do old tubes sound better than current tubes?

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.

The best answer I have ever heard is that some of the coatings used in the olden days are too environmentally unfriendly to be used in modern production. Another thing that you cant discount is the knowledge gained by experience of the toobe makers of old; trade secrets, lost in the sands of time :) Also, people were forced to use their BRAINS in those days.

I am happy to hear that at least some new production tubes are getting rave reviews but I remain skeptical about preamp tubes. I have seen so called preamp tube shootouts where the reviewer tested one tube of each type and drew concrete conclusions from such a limited sample. Anybody who has ever built gear or rolled a lot of tubes knows that two good preamp tubes from the same production code can sound vastly different - not to mention sonic differences due to minor changes in plate and heater voltages.

Mike

Disagree, kind of. While today's output tubes are really quite fantastic, the small signal tubes just do not compare to vintage. You can pretty much take any type of small signal tube, nine pin, octal, whatever, and vintage tubes will sound better.

My experience and that of many Doshi Alaap (preamp) owners is diametrically opposite to Viridian's, which leads me to believe that the design of the component is a critical factor in which tubes work best.

If a component is designed and executed from the ground up with a modern tube in the circuit, as Nick's designs are, then that tube may provide the best performance. I've done plenty of NOS tube rolling and Nick and other owners have done more. I've found one vintage line stage tube that slightly outperforms its current production equivalant in some sonic areas, though not all. But in both phono stage tube positions no NOS tube compares with readily available, fairly inexpensive new tubes from the likes of JJ.

In a vintage component, or a modern component designed around vintage tubes, the opposite may apply. I doubt there's any other hard and fast rule about old vs. new that we'd get much agreement on.

thanks for the responses, all - this was quite informative. i ask as i have just purchased an aesthetix calypso and find it to be an exceptional preamp, however, have read that tube rolling with particular NOS tubes can make it even better. i was considering telefunkens, but was curious as to what it was specifically that made the old tubes sound better. sounds like there's some lore/nostalgia, some materials, and some design (component and tube) that factor in here.