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

I have to say we have had extremely good luck with the run-of-the-mill Chinese 6SN7. We've been using it for about 14 years. Its not the best sounding tube, but its not bad, and they've been pretty reliable.

Anyone want to start a tube factory, I'll put up the funding if a couple of grand will get you started.

I confess I use Mullard CV4024s, but mostly because the JAN Phillips 12AT7s they replaced self destructed after about a month, and I like the "start-up flash" the Mullards display...we need more tubes with that start-up flashing...it's exciting. Note that the EH 12AT7s were fine, I was simply overcome with curiosity. I do like the new Mullard 12AX7s in my Burriss guitar amp, but they, sadly, don't flash on start-up.

All these new tubes are basically 845,300B, etc. If your looking at signal tubes like 12ax7,12au7,6922,6SN7, etc. the new old stock from the 40-60's sound way better than any tube from China or Russia in my opinion.

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.