@bigtwin I think the answer was supposed to be the transistor but I've been around long enough to remember how much better the ARC SP3 preamp sounded than its solid state competition in the early-mid '70s. And, insofar as tube manufacture is concerned, I think it is a combination of things: materials and worker safety, tooling and loss of know-how for what is at best a now a niche market. That tubes were still manufactured in the old Soviet bloc had less to do with their belief in old technology than it was their inability to modernize. Sure, there are similar issues with rare earth materials involved in semiconductor manufacture, but the tube is obsolete and as such, people go back to the days when they were still a mainstream product. Did you ever see those old newsreels on video of the production of Mullard tubes? Fascinating- it was like a steampunk assembly line.
Here's one: https://www.youtube.com/watch?v=GDvF89Bh27Y