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I first became aware of the Russian Numitron tube when I found several build logs where it was used as a low-voltage seven segment display in clocks; they’re sometimes billed as a “low-voltage Nixie tube”. I bought a handful of them from a seller on Ebay but mistakenly assumed all Numitron tubes functioned in the same way. In most of the builds I had seen, which used the IV-9 tube, a voltage is applied to individual filaments which comprised each of the segments.
The tubes I had ordered were IV-3A tubes, a vacuum fluorescent display, which consist of a directly heated cathode, a grid, and multiple anodes corresponding to the various segments. The anodes are coated in some mix of phosphorescent chemicals which illuminate as they’re struck by electrons from the cathode.