alt Hacker News Droitwich uses two metre-high ceramic and metal valves,
which are no longer made.
from: https://www.radiorewind.co.uk/radio1/droitwich.htm
https://i0.wp.com/www.richardmudhar.com/blog/wp-content/uplo...
"valves" being british for vacuum tubes (though there's an entire generation of scifi where future computers are built around miniaturized valves even among american authors for some reason, Asimov in particular)