Why do old tubes sound better than current tubes?

Almarg, if you will open NOS, on Mapmans post dated 08-23-10, and then read my post above his which was posted before his post; you will be able to reach some very interesting conclusions.

One of the Chinese tubes, the Suguang 12AX7 is as good as NOS or better than other new for sure. I swapped some out and quickly swapped them back in.

Viridian, we found something we can agree on; I think. New tubes do not even compare to NOS tubes. NOS tubes can take gear to another level. Let me be specific; I am referring to preamp tubes, those are the one's I have had experience with.

I claim to have golden ears in regard to NOS tubes. I bought some bargain NOS tubes that sounded half as good as full price tubes and I sent them back for full price tubes. MY point is, leave bargains for the bottom feeders.
I have bought tubes from "Brent Jesse" for years. A reputable dealer makes his living dealing with "golden ears", he can not afford not to deliver the goods. Since there is absolutely no way to tell an OK tube from the real deal by looking at it, and only if you got the ears can you tell by listining to it; your best option is to only deal with a reputable dealer.

Almarg, a 5963 is equivilant to a 12au7. Would a pair of 12au7's Gm 1, 2800 Gm 2, 2850, NOS RCA Cleartop be in the ballpark of what you are referring to.