I have seen quite a few nixies where one or more digits won't light at the normal striking voltage, especially tubes that ran for some time in applications where some digits are not lit. I found that running the digit at higher than normal voltage and current until the digit is fully formed, and gradually decreasing it will restore about 70-80% of problem tubes. afterwards, they run fine, and even days of continuous digit operation shows no further trouble. the 8 seems to be an especially fault prone digit, probably because of the large area.
the current theory is that some sputtered metal and other residue from lit digits collects on un-lit ones, and creates an insulating layer, this can be burned off and removed by over-drive for a brief period. I use DC from a regulated supply, and have never even considered AC for this task, as I believe it would harm the anode. Usually 200+ volts will strike and fully light the bad digits, and I reduce the current limiting resistor to 10K/1W. after a few hours, the lower 170 voltage should still give full and bright coverage, and the tube should still work at higher series resistance. a re-check after months of storage shows the tubes are generally still good, with maybe a 5-10% re-fail rate. sometimes this requires baking over night. tubes get warm during this process, but will not be damaged if the resistor is still present. Interestingly, this will also sometimes fix base flashover on large tubes, which can be caused because the bottom path is easier than the regular digit path for current flow where the digit is poisoned. over-drive will sometimes restore the digit path, and eventually allow drive to be reduced without the bottom flashover. this does not always work, but I have been amazed to see it bring back many used tubes. generally, new tubes that exhibit this are flawed in manufacturing. low gas pressure, bad manufacturing, blackened faces from over-drive and other issues can't really be corrected, but certainly some problems can be fixed with a good power supply, although it is not unusual for this to take days to fully correct. storage and re-test after at least 30 days is recommended, to be certain the tube is really repaired. all the best, walter shawlee sphere research -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msg/neonixie-l/-/Qr36tBiBTZ0J. For more options, visit https://groups.google.com/groups/opt_out.
