I am fully prepared to offer a loving and caring home to all ugly B-7971s! On Friday, 9 August 2019 23:53:01 UTC+1, gregebert wrote: > > 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. > >
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