Wow, these tiny Korg valves look amazing: https://korgnutube.com/en/

I wonder how long it’ll be before someone makes a radio with them in.

https://korgnutube.com/wp/wp-content/uploads/images/omote.png

It looks like RS are selling headphone amp kits which use them https://uk.rs-online.com/web/p/analogue-development-kits/1813534/

Expensive though!