I designed and built my own 8-tube 7971 clock; it's been running over 2 years now and the only tube failure was caused by a segment moving in the tube and contacting another one. Nothing has failed due to the actual design of the clock.
So, yes, the datasheet specifies a maximum current for all segments, and you should not exceed that. As you probably noticed, there is a spec for the various segment currents because there are several different lengths, hence different operating currents. If you add-up the total current for all segments at their rated maximum, you will draw about 40mA, which is almost twice the spec limit. I did some spreadsheet analysis of how much current each displayable character consumes, and not surprisingly most of them fail the 21mA limit. What I did was to scale-back the individual segment currents so that most characters are below 21mA. For the few that would otherwise exceed a total of 21mA, there is a second current regulator on the anode set to 21mA. For those characters, the current gets shared so each segment gets slightly dimmer. For each tube, I plotted I-V curves and found that the observable brightness does not vary significantly between 50% to 100% of rated current. I also used this data to confirm tubes have similar characteristics. There is potentially some risk that cathode poisoning will occur at reduced current, but I have seen no hint of it. On the other hand, I definitely see it with IN-18's but that's a different story.... I gave away my extra PC boards; I dont know if the folks on neonixie who have these boards have built theirs yet. I like the fact that these tubes are enormous and you can display text, but I have to say they are quite ugly. Nothing compares to the beauty of a fully-figured traditional nixie. -- 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/438352ea-cef1-46be-b47e-7598d89d33bb%40googlegroups.com.
