Why do NOS Tubes sound better than new tubes?


Is manufacturing really that backwards in todays techno world? What is the real reason that todays tubes cannot equal the tubes of yesteryear?
tubed1
Back then everything depended on the tube quality and stability whereas now there's an improvement of circuit engineering.
This was posted recently. You could see in the old videos how much they tried for quality. [http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1314237934&openusid&zzHifihvn&4&&]
Lots of manufacturers back then A lot of competition
Now only a couple plants make tubes. No competition
Not all NOS tubes sound better than new ones. The ones that do are because of the reasons cited in the above posts.
Agree with Tpreaves. I've replaced Mullard xf1 EL34s as driver tubes in my SET monoblocks with current-production Genalex Gold Lion KT77s because they sound better. OTOH, NOS tubes are often preferable. But it's not a sure thing and always worth trying the new ones.