Having started my ham activity at a time when valves were still reining in the world of electronics, I feel a lot of nostalgia for that technology. When I settled in Chile in mid '80 I realized that it was a sort of time capsule where I could find very old equipment to collect at quite reasonable price. I spent quite some time restauring some of them.
An old desire of mine was to construct a radio that could work after a strong EMP. This should of course not make use of any semiconductor.
For long time I did collect part for making a radio out of 12V (anodic) tubes, the ones that were created for the last attempt of competing with transistor in car radios. I remember my dad had one for some time.  As it often happens, once I had the time and came to the design board the project was aborted when I discovered the outragious amount of filament current needed to provide decent gain. This would make its use unpractical outside a running car (that likely would not run at all after a strong EMP).
However, looking for proximity sensor schematics, I realized the potential of the submini tubes, that were designed for anti-aircraft shell at the end of WW2.
Quickly the idea of a radio that could be powered by 2 or 3, at most, 9V batteries became appealing. In Ebay I could easily purchase the variety of tubes I need for a basic superhet.
But before I could do some serious project I needed the valve specs. So I decided to build a curve tracer. The project took some time. However, when I had a working prototype, I already found the info I needed from various sources online, so I did not procede further.