I used a 2.5VAC transformer for my NIMO clock, and use series dropping resistors to get the correct current. Those filaments run at 1.1 VAC and 200mA. Using AC cancels-out the brightness quirks when using DC. The series resistor will reduce the power-on current surge and therefore extend the filament life, at the expense of added power. Finally, at least with the NIMO tubes, I have individual series fuses, along with logic and software to monitor the condition of the filaments, resistors, and fuses [yeah, yeah, it's overkill, but I had a lot of fun designing it....]
I do have several VFDs waiting for me to design clocks for them...just need the time. On Friday, August 20, 2021 at 10:01:27 AM UTC-7 [email protected] wrote: > Sorry for not being helpful, but I'd love to see your digivac clock when > you're done! > > On Fri, Aug 20, 2021, 12:58 PM Paul Andrews <[email protected]> wrote: > >> I'm designing a clock for DT-1704 tubes and am stumbling at the filament >> drive stage. They want 1.6V. I want to power it from 5VDC. I've tried >> wiring them in series, but there is a noticeable brightness gradient if I >> do. I've tried powering them using a LM4871 to generate a square wave with >> 1.6V RMS, but the voltage drops as I add more tubes in parallel (an aside: >> why is this? I know it is specified to drive a 4 Ohm to 8 Ohm load, so I >> assume that is it). I don't want to dump a bunch of heat through a LDO or a >> stack of diodes. So I looked at making a buck converter. >> >> If at all possible I would like to re-use the design for other VFDs, e.g >> for VFDs that want a grid to be pulled below the VFD voltage, and I would >> really prefer to use AC rather DC so I can use it for multi-digit VFD tubes. >> >> I thought that if I made the buck converter output isolated I would end >> up with a solution that would be more re-usable for different kinds of >> VFDs, but naturally I hit the issue of what off-the-shelf transformer I >> could use. I also got to thinking that the output diode of a buck converter >> that produces 1.6V is going to drop a significant part of the total >> voltage, which made me wonder why I should even try to rectify and smooth >> the output given that an AC filament voltage would be better anyway. Then I >> also wondered if such a solution would hit the same problem as the LM4871 >> design, i.e. dropping voltage as I add more tubes in parallel. >> >> So I would appreciate any suggestions for what direction I should take >> here. I have too many options and no clear criteria. >> >> -- >> 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 view this discussion on the web, visit >> https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/neonixie-l/860d4d78-c807-415e-a740-b576a4b5d18cn%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/630a73fd-8036-43ef-bda6-af5bd42f3dffn%40googlegroups.com.
