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

Jwm, I sort of agree although there are great sonic differences among the NOS also. I think either the skill of those who were making the NOS or the QC then with many tubes discarded.

Yes of course the RCA's sound different than the Sylvania's. I don't know why that should be the case since factories know the specs on how the tubes should be made. It may be slight differences in materials or tolerance in the parts.

I'm encouraged by the sonics of many current production tubes, especially some coming out of China. Many rank right up there with the legendary tubes, though more often than not, the old American and European variants still hold the edge in absolute terms. From my experience, I think it's in ruggedness that the old tubes hold a big advantage, particularly over many current production European tubes.

Shuguang tubes possess the best reliability in the industry reliability over the past decade. While the premium Chinese products get most of the attention, the run of the mill Shuguang 12AX7B, EL34B, KT88, and 5AR4 offer surprising sound on top of that reliability. Speaking of surprising, the dirt cheap NOS military Shuguang metal base 6SN7 (labeled 6N8P) will as well.

Personally, I find buying old used tubes that most pass over in favor of spending a lot more for NOS finds on sites like ebay to offer tremendous sonics, longevity, and overall value.

Lost art. That's why. New stuff can be very good, but will always be different. I wish some of these way-to-damn-rich philanthropists would occasionally pick a dying (beautiful) technology to keep alive (like vacuum tubes back in the 60's-70's) -- rather than the trendy shlock they typically flock to -- in order for future generations to rediscover some of the beauty and knowledge that has been created by our predecessors.

A lotta folks think all tubes sound the same, or essentially the same. Wouldn't vendors selling new tubes be inclined to market their product as being superior to NOS tubes, just like the NOS tube vendors, you know, for the profit to be made? Gosh.....another audiophile debate in progress. As for myself, I'll stick with WWII tubes from Sylvania and Tung Sol. Y'all can divvy up the new stuff. :-)