My first guess is a bad tube; I cant tell from the picture if they are socketed vs. soldered. If they are socketed, try swapping tubes. Second guess is the high-voltage power supply is just a wee bit low. Not all tubes ionize at the same voltage. Try measuring it; should be 180V or more. If your clock is multiplexed, it's possible though unlikely the anode driver for that digit is weak. If it's direct-drive, it's possible though unlikely the anode resistor overheated and it's resistance increased.
I have a few tubes that have poorly-lit cathodes; they were in a batch of used tubes of unknown origin and I suspect they are at the end of their life. I can't rejuvenate them, either. I doubt your tubes are in this condition being only 3 months old. -- 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 post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/fb153a8f-eb60-4dd0-8863-319934b6cd5b%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
