A lot of people like tubes either for their audio sound or their collectible value. [Uniservo] likes oddball tubes. His recent video (see below) shows a radechon — a computer memory tube. These were apparently widely used in RADAR sets until recently and has some similarity to a Williams tube.
The tube is essentially a CRT that illuminates a sheet of mica or another dielectric instead of a phosphor screen. The dielectric has a fine mesh grid in contact with it. By depositing charge on the mica, the tube can store an analog value. In theory, the tube could store about 16 kbits of information, but in practice, the resolution was less.
The charge would persist for a few hundred milliseconds and the memory system would have to refresh the tube contents or the tube would lose its data. For binary storage, the surface gets a negative charge, or a zero charge. Some tubes used a capacitive coupling to the charged surface, while others would collect secondary electron emissions from the front of the surface.
We found a scan of a Radechon data sheet on [Nixiebunny’s] site. On the Cold War Infrastructure site, there’s a scan of an RCA ad for the beast, showing a picture of SAGE that apparently used the tubes. There are also links to some other pages about the tubes.
If you are interested in old memory tech, we took a trip down memory lane last year. We aren’t sure if you could do the same debugging trick with these that you could with a Williams tube. With those, you could hook a CRT in parallel with the tube and get a visual representation of your memory, a trick used by Baby and several other old computers.