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

I have always thought it was quality control. I know that Chinese tubes are sorted by quality and sold at different prices. I suspect that many tubes in an earlier era were merely discarded. I remember radio stations buying tubes in big boxes and plugging them in side by side. Those that didn't glow were quickly discarded.

I also expect that the women who made them became quite skilled and consistent. I doubt if that level of skill is available today.

One thing is for certain the old NOS tubes of even the 1970s are become rare as hen's teeth.

The tube manufacturers of today have lost the "old formulas" for making quality tubes. The Russian tubes of today were formulated on "Military" tubes designed to keep Migs flying through "atomic clouds"!

There was a link on the new Mullard site worth checking out. It showed the process of making tubes in the 50/60's. Watch that and you will understand why a) they don't make them like they used to and b) why there was a big push to go to transistors. The amount of machinery, the precision necessary at every step, and the error/failure rate even at the Mullard factory are fasinating. That said, some of the new manufactured tubes are pretty good and seem to be getting better.

It would seem by trial & error over the years that there should be no problem manufacturing a superior tube. Even the machinery involved in producing tubes could be compacted, streamlined, and improved given this computer age. It may simply come down to supply & demand, maybe not enough orders to justify the factory investment. Audiophiles represent a small segment of society, thus the demand is not that significant since a tube's primary application is an audio circuit.

Quite simply because life and death no longer depend on the quality of a vacuum tube, the way it did back in the hay days, during WW II, when tube technology drove design and manufacturing to the maxx.
We now just use tubes for a casual hobby, lives are no longer at stake, so there is a HUGE loss of military funding for vacuum tube design and manufacturing quality standards.

Cheers,
John