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

...and the fact that there was competition among manufacturers.
Tbg (System | Reviews | Threads | Answers)

I believe this does without saying. Every tube manufacturer would be competing to produce the best products to win the available military contracts.

I heard that RCA used the same machine to make tubes for 50+ years and every year the fittings got looser and looser so the newer tubes lost a bit of quality each year compared to the original tubes. I forget any more specifics but the general idea makes sense to me (in this instance). This is one part of the equation it seems...

It is my understanding the materials have a lot to do with it, but I believe there is an art to manufacturing tubes and even though the same equipment is used there are different people involved in the manufacturing process.

When you guys talk about "better" that include sound quality?.

Tubes these days are fired incorrectly so there are contaminants caused by the getter being under or over-fired.

Cathode structures are not being built with proper care. Contaminates get introduced, causing grid contamination during the operation of the tube and also causing arcing as the cathode coating flakes off the cathode.

There is a new US manufacturer of tubes in Carson City, NV that was showing at THE Show just last month. They are starting with a new 6L6 and expect to have a KT88, 2A3, 300b, 6SN7, 12A-series. They seem to be well funded. RCH Labs. The 6L6s they had on display looked quite nice :)