My driver circuit is a direct-drive constant-current source, and it was set to the IN-1 spec current of 3.0mA. I was only using one numeral in each tube, so all undriven cathodes were floating. The clock uses 15 tubes to display 1 thru 12 on the clock face (it's a large neon-equivalent of a regular mechanical clock) so the numeral is displayed constantly.
What I found is that after a few days there would be 2 glowing cathodes: The desired numeral, and the adjacent cathode closest to the front of the tube. I confirmed a low-resistance short of a few ohms was present. I kept a lot of notes, but I would need to dig around for them. I also found that the short was caused by a tiny filament that formed between the cathodes by passing about 100mA which caused it to glow. It usually took 300 to 500mA to zap the short; it acted like a fuse. Afterwards the tube functioned as expected. As I ran my clock longer, I noticed more tubes failing in the same manner, and each time I was able to zap them back to life. It got ridiculous having to zap another tube almost every day, so I replaced them with Burroughs tubes and never had any trouble. I suspect the filament was growing in the direction of the electric field between the cathode and anode, and grew until it shorted the adjacent cathode. I dont have the equipment to analyze the chemical makeup of the cathodes or the filament that formed. I do know it was very small diameter; not visible until it was made to glow. NASA has done considerable research on tin whiskers, which is probably a similar mechanism to what was failing in my IN-1 tubes. They form in electric fields. I've heard that IN-1 tubes do not contain mercury, whereas Burroughs (and many other brands) do contain mercury. Perhaps there is some odd role mercury plays in preventing the formation of these filaments. I suspect that after the USSR broke into separate nations that different materials or processes were used in IN-1 manufacturing; there may have been relaxed quality standards as well. My tubes are all date-coded 9205. I have an A101 dekatron spinning 24/7 on the same clock, and it's been running flawlessly for more than 2 years. Despite a much higher operating voltage (hence higher electric field), it's fine. -- 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/53216fa6-0cd4-4b97-a0e1-7b0daccf73e6%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
