David “daqq” Gustafik from Bratislava, Slovakia wrote in with this excellent robot. It uses mostly harvested parts, including old motors pulled from an East German printer. But the centerpiece of the design is a tiny monochrome CRT.

The CRT tube itself is a Tungsram DG7-123. It’s an old CRT, meant primarily for scopes. It’s got an indirectly heated cathode, all plates separated, and a lot of nice features. It’s also quite sensitive. If you’re familiar with the Tesla 7QR20 you might recognize this as the more advanced version. Physically they look identical, but the Tesla 7QR20 had a directly heated cathode, two plates connected together with the anode, and something else bad. I got it on an electronics flea market in Bratislava I visit often.

Providing support for the CRT proved to be quite difficult – not only were magnetic fields a problem (various picture distortions), also it needed to be in a specific angled position so the user could see the picture. Oh, and it’s also very fragile, which meant no screws. In the end I chose a simple solution – the basis of the holder is a plate from an ancient hard drive. The bottom is slightly bent and has two M4 holes drilled into it – for attaching the whole plate onto the main chassis. The disk was chosen also for convenience – it’s got a nice little hole in the middle – which is almost exactly of the same diameter as the main body of the tube, just a little bigger.