Hi, some years ago I aquired 7 small Nixie tubes, the markings have gone, but on one there can be seen a faint Hitachi logo. I have attached a pic of one next to a Z5900M for size comparison. I thought they must be CD71 type, but I also have 1 (just one!) tube that is clearly marked CD71 with the Hitachi logo. It is fatter though, and has a very open anode mesh, at 12.5mm dia, whereas the mystery tubes are only 9.4mm dia.
5 of 7 mystery tubes work fine. Of the other 2 0,ne has a broken anode lead, and the other appears to be dead. The leads on them are quite oxidised and are a bit brittle.
I will never do anything with them, so if anybody - prefaraby UK - wants them, let me know.