The tube circuits I studied were marvels of clever engineering.

Yes! Vacuum tubes seemed much more predictable than semiconductor devices. I don't remember exactly why, but perhaps it was that the tubes had more linear behavior than the SSDs. Regardless, I'm also happy that I learned about those amazing things. It's such a shame that they were dropped in all cases where SSDs replaced them.

There were some efforts to create ICs with vaccum tubes of micrometer sizes. At those sizes, they don't need heating or vacuum hermetic sealing like the traditional large tubes. But they retained one big advantage over SSDs - they have superior fault resistance and survivability against radiation. That makes them prime candidates for space and nuclear applications. This was like 15 years ago. I thought that they would hit the market for sure by now. I wonder what happened to them.