I don't know the specs for these specific tubes, but a resistor in series with the filament servers a couple of purposes:
1. It reduces the inrush current (i.e. when the filaments are cold). The resistance of the filaments is low when they are cold, so if you put the steady-state voltage across them in that state, there will be a much greater current. For this purpose the series resistor value should be high enough to drop that current within the specified limits of the filament. 2. Putting a resistor between 0V and the filament raises the base voltage of the filament above 0V. If the tube has a grid, it is typically specified to be at a negative voltage with respect to the filament so that it can be guaranteed to cut off the current when pulled to that voltage. An easy way to achieve this negative bias is to raise the filament voltage above 0V and keep the grid at 0V. 3. On Wednesday, September 14, 2022 at 4:16:12 AM UTC-4 Richard Scales wrote: > I think I already see blunders in my original post - the filament is the > cathode (I think) at 5V, the segments (individual anodes) at 25V giving a > 19V difference over the grid which is at 5V. > I am unsure as to the correct value of the series resistor for the > heaters- 10R has been used by others though I would prefer to know how that > was calculated and indeed whether there are significant gains to be made by > moving to an A/C drive for the filaments. > - Richard > > On Wednesday, 14 September 2022 at 09:02:24 UTC+1 Richard Scales wrote: > >> Hello everyone, >> I have just managed to acquire a set of these and would ideally like to >> drive them the best possible way. >> I had initially though about a 5V for the filament and then 24V for the >> cathodes and grid. >> The clock would only have segments activated when someone is nearby - the >> segments will not be left on all of the time. >> Now I read about A/C supply to the filaments and wonder if I should be >> going that way. >> Would anyone be able to post their findings and/or suggest the right way >> forward? >> [image: VFDsnip.JPG] >> >> I just noted that the picture above shows the connection for the grid >> (pin 9 on H1) connected to 5V and not the 24V as used on the cathodes. >> The more I think about it - the less clear this all becomes! >> I need to get it right in my head before I go breaking something and then >> I would like to get the best possible result via reasonably straight >> forward means. >> Would anyone be able to point me in the right direction and/or share >> proven drive methods? >> - Richard >> >> >> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote: >> >>> Yes! That's exactly what happens. The current through the center-tap is >>> the sum of the anode (segment) current and the grid current. And the peak >>> current through the filament wires is actually *greater* than just the >>> current to heat the filaments. >>> >>> >>> *Tomasz* - As you found out, those VFDs draw a lot of current. I have a >>> future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) and >>> I'm just going to use a high-current filament transformer with the >>> center-tap at GND. Grids will NOT be pure DC; closer to full-wave rectified >>> around 15-16V. Segment anodes will be pure DC around 36-40V with >>> current-regulators and non-multiplexed. >>> >>> I actually have an Op-amp summer+ADC+Software to monitor the current >>> thru the center-rap on my NIMO clock to determine the tube health, though >>> it's orders of magnitude smaller (30uA per tube). >>> >>>> -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/9c35abb5-4869-41e3-92b4-a27dc0266ce3n%40googlegroups.com.
