The old-school method used was a thermistor in series with the heater chain, chosen with a suitably high resistance when cold which would slowly drop as it warmed up to a low operating value.
Tony. On Mon, 22 Oct 2018 14:10:40 -0700 (PDT), you wrote: >Congratulations on acquiring 6 NIMOs !! > >I've gone thru all the NIMO filament analysis and came up with the >following, which I have implemented in my design > >1. Transformer is 2.5V CT, 3A. Triad F301X.. It has dual primaries so it >can operate on 115 or 230 VAC mains. >2. Series fuse 250mA (BEL C1F250). One for each NIMO >3. Series resistor; empirically I'm choosing 6.8ohms. > >The filament is the most-critical reliability-impacting element of your >NIMO tubes, so be extra careful to make sure you design with this in-mind. >Filaments usually fail due to power-on surge-current, just like >conventional incandescent bulbs. The surge-current is the result of the >lower-resistance of a cold filament being the only limiter of current. For >example, measured NIMO-tube filament resistance varies from about 2.8 ohms >cold, to 7.0 ohms when stabilized at 200mA. If you use a constant voltage >to power the filaments, you will have significant surge current. But if you >add some series resistance and drive from a higher supply voltage, the >surge current will be less. With the components I listed above, the surge >current is about 260mA. > >The fast-blow fuse will protect the NIMO from line-surges, or other >uncontrollables. > >I'm almost done with my NIMO clock, and I will collect waveforms of the >power-on transient for each filament once I get my other tubes (I have 1, >need 5 more) -- 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 [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/3gossddqt5anvd1leui3050264fp9tqnbh%404ax.com. For more options, visit https://groups.google.com/d/optout.
