Toward the very end of the vacuum tube era, there were some "almost solid-state" tubes created, and mainly only used on televisions. You could find old TVs that

Toward the very end of the vacuum tube era, there were some "almost solid-state" tubes created, and mainly only used on televisions. You could find old TVs that had parts which were transistorized, and others that had these "tubes". Except they didn't quite look like tubes: https://en.wikipedia.org/wiki/Nuvistor https://en.wikipedia.org/wiki/Nuvistor They were almost the size of then-contemporary transistors; just a tad larger. They were made in a special process (inside a vacuum chamber). Pretty much the zenith of the technology, and showed what it could be pushed to do.