It has to do with the voltage difference between the deflection plates and the anode or cathode. From what I recall, the max voltage difference between the deflection plates and the anode is only a few hundred volts (much less than the anode-to-cathode voltage to produce a visible beam), so that leaves 2 options:
1. Make the cathode about 1.5kV negative, so that the deflection plates are driven at voltages closer to 0 volts, and drive the anode at a few hundred volts positive. 2. Keep the cathode at GND, drive the anode around 2kV, and make the deflection plate drivers capable of operating at a much higher voltage. You basically need a level-shifter. >From a circuit perspective, #1 is generally easier to implement. David Forbes (on this forum) has a very good scope-clock design. On Monday, October 27, 2025 at 9:41:40 AM UTC-7 Tom Katt wrote: > Hello all - long time lurker, new member here. I've built several Nixie > clocks over the years and am now looking at building a crt based 'Scope > Clock'. I've built a low voltage clock that hooks up to an old crt scope > and now I'm looking into building a dedicated clock with a 3RP1A crt tube I > have on hand. But I don't know the best way to go about powering the crt - > I understand that I need about 1KVDC, but searching the web it seems like > some designs have a negative high voltage for the cathode end and others > have a positive high voltage at the anode / deflection end. I'm trying to > understand why one approach is preferrable to the other. > > Any thoughts or suggestions would be appreciated! > > Thanks! > -- 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, visit https://groups.google.com/d/msgid/neonixie-l/baeb6dd7-ec12-44d9-9fdf-80464193b7a8n%40googlegroups.com.
