Sadly, both tubes got tossed with the trash before I even made this post, so no autopsy is possible. That said, I did inspect them visually. There was definitely no visible darkening of the tube, but I couldn't get a good look at the base of the cathode due to shielding. I would have noticed sputtering (which I looked for) after the first failure when a new tube was side by side with a tube destined to fail. The older tube was not noticeably dimmer than the new one.
Signs indicate that erosion is the cause however, because of said "tink" -- The question is, could the sputtering have been confined to the area very near the cathode? Plus, it would make sense that the "low scale" portion of the cathode experienced much more erosion than the high scale, as the control portion of the system has an auto high voltage power off after 30 seconds but it would turn on when there were random transients (ground bounce, etc) during the day, and then go back to sleep. During that time, the tubes would be on for 30s with 0A control current. Perhaps that was bad for them. I'll run a test / video for everyone with controlled current over the weekend -- to demonstrate bar length at 0-15mA control currents. On Monday, January 23, 2017 at 1:57:18 PM UTC-8, Jon wrote: > > > Sounds like a good excuse for a tube autopsy... > > If you are indeed over-driving the current then you'll be sputtering > material off the cathode which after a while will have two effects. Firstly > there will be some gradual darkening of the tube as the material deposits > elsewhere. And secondly you'll see gross physical erosion of the cathode - > you can see a similar effect on dekatron cathodes where the glow has been > sitting stationary for a very long time (usually the zero cathode of the > tubes making up the higher order decades of a multi-tube counter). Given > that you describe a 'tink' noise, my guess is that the cathode has eroded > to the point where it physically broke, perhaps under the thermal stress of > being activated. Time for new tubes. > > The Soviet datasheets only promise 1000 hour life for IN-9 - I can't find > a similar overall guaranteed life specification for IN-13. My experience is > that they will last much longer than that if not overdriven. > > With regard to the current required to achieve full scale, yes there's > normally some cathode poisoning which needs to be burned off when you first > fire up the tubes (worse on IN-9 than IN-13), but then they should settle > down and operate at the specified sensitivity. The last centimetre or so of > the cathode is difficult to illuminate even in a well 'oiled' tube - they > lose linearity at the upper extreme. Best thing to do is not to worry about > trying to light up this bit. > > 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 [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/02250be3-13e2-4b03-b683-d7827ba28ec5%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
