Bottom line: Keep the current as low as possible, and limit the inrush current.
I've done a fair amount of research on extending filament life for a project I'm working on. After a lot of tradeoffs and analysis, the best solution for me was to use a *higher* operating voltage and add series resistance. This reduced the peak inrush current, was the simplest design, and the added energy cost vs a "perfect" constant current source was less than the circuit cost for the regulator. This project uses 6 tubes, and each tube has it's own filament fuse, and an FPGA to monitor the condition of the fuse, filament, and the dropping resistor. I can also measure the filament current on 2 tubes the an onboard A/D converter. Here's a technical paper on extending the filament life of expensive transmitter tubes, and inrush current was the #1 killer. Reducing the filament current even a few percent resulted in much longer lifetime. See https://www.photonis.com/uploads/literature/pt/Voice-of-America-Paper.pdf >From my own measurements, a filament's resistance varies substantially when cold vs. hot The tube I'm working with varies from 2.8ohms (cold) to 7 ohms (hot). So there's roughly 2.5X the surge current on this particular tube if you drive it from a constant voltage. The technical paper above reported variations of 10:1 for transmitter tubes, and 12:1 for incandescent bulbs. On another project, I have a #47 bulb driven by a current regulator. It goes on/off 24 times per day, and has been running for 2 years now. And, it was a used bulb so I have no idea how many times it has been cycled. But it's still working. The current regulator definitely cause the bulb to light more slowly. If you want to read about a really long-lived filament, check out the story of the lightbulb in a fire station in Livermore, CA: http://www.centennialbulb.org/ -- 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/d1c53f7e-d533-4280-bf06-e18aa5dd9c73%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
