I've built quite a few Numitron clocks, most with the common (and inexpensive) IV-9 tubes, but a couple with the large, attractive *top-view* RCA DTF-104B tubes (which are pretty rare now). I'm currently working on a pocket watch using the diminutive Minitron displays (about the size of an 8-pin DIP).
My clocks use an 8051-derivative processor, direct-drive using 74HC595 shift registers. It was a bit of a pain, but to extend the life of the tubes, I keep all of the filaments heated even when visibly "off". The "on" segments are heated to whatever the desired brightness is, using a look-up table for a PWM ratio of 3:32 to 1:1 (the perceived brightness is very non-linear to the actual on/off ratio). The off segments are excited with a 1:32 ratio, which is just below the point of a visible glow - in a completely dark room, after my eyes have dark-adapted, I can just barely see a dull glow from the "off" segments. I hadn't thought of using current limiting during the initial warm-up, though... Note that even without this sort of gentle treatment, these tubes have very long life-spans. The US tubes (RCA Numitrons, Apollo IEE-series, or the Minitrons) all have a specified life expectancy of 100,000 hours at full drive voltage, and it goes up dramatically from there at lower drive voltages. Also, they're surprisingly rugged mechanically: rated peak acceleration *during operation* of 100g, and continuous operation with 20g vibration from 5-500 Hz - these things were designed to be installed in fighter jets. Add in the fact they're readable in direct sunlight, and one can see why it's only been in the last decade or so that the Minitron displays are finally disappearing from airplane cockpits. ~~ Mark Moulding -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to neonixie-l+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/907f295d-044a-450e-9f56-412342f9c0c0%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
