Pin 8 is better called the common cathode - it's connected to all the main cathodes except K0 (pin 1), K3 (pin 7), K5 (pin 5) and K9 (pin 6).
I guess K0 is what you might instinctively call the index cathode, but because the array is circular it's a bit of an arbitrary designation. For any of K0, K3, K5 and K9 if you start with the glow on that cathode, conduct 10 stepping cycles you'll wind up with the glow back on that cathode. So if your application just involves using the 'index cathode' as a reference point from which to count steps or complete revolutions, it doesn't really matter which of these four you use for that purpose. The most logical one to choose may depend on physical considerations such as the orientation of the tubein its mounting and therefore which of those cathodes is closest to 'up' or whatever rest position you might want to use. This type of tube with some but not all main cathodes brought out onto the base is often referred to as a 'computing counter' as distinct from a 'counter' (one index cathode and nine commoned cathodes) and 'selector' (all cathodes individually available on the base). The ETL datasheet for GC10/4B has a useful table that shows how you can use this type of tube to count any number of pulses from 1 to 9. Cheers, Jon. -- 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 post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/ee99c87d-34cc-4e01-972c-4917dd4920d1%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
