Nixie IM 9 Thermometers- cathode poisoning possible?

[Dman777]

I am curious about Thermometers that use the Nixie IN 9 tube.... since the temp is steady and doesn't change that much...how does one keep from cathode poisoning happening to the IN 9 tube?

[gregebert]

Are you referring to the linear IN-9 tube ? I experimented with a few of those and was very disappointed with their erratic behavior. For example, I could get half of the tube to illuminate with 5-6mA. When I disconnected & reconnected it, the reading was different. If I left it on for awhile, with the same current, it would drift. The deal-breaker for me was when I would crank the current up-and-down, and sometimes it would start glowing from the opposite end.

I sure hope these weren't used in critical applications, such as monitoring a nuclear reactor.....

[threeneurons]

Even the IN-13, with the extra "hold down" cathode, has problems after running continuously over a long period.  One of my friends bought one of those kits, were the glow just grows, and shrinks, alternately. Its still working after about a couple of years. But in less than a year, it would no longer lock at one end, as its suppose to. The glow center, now sort of drifts toward the middle. It now grows and shrinks outward in both directions. Kinda cool, if you didn't know, how it was intended to work.

[Darin Hensley]

Wow, I was worried about cathode poisoning but it sounds like there may be even more worries. If I bought a Nixie thermometer IN-9, the tube wouldn't lastlike a normal Nixie tubes? 

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[gregebert]

Your mileage may vary, but my experience with the IN-9 shows it to be power-hungry and unpredictable. They are quite dim for the amount of current they draw, and they also get a bit warm.

I would suggest making your own with a string of NE-2 (or similar) bulbs. The obvious solution is to have an individual driver-transistor for each bulb, but I'm sure there are clever ways to do it with fewer drivers than bulbs.

Ughh, the creative wheels are turning inside my twisted brain now......sounds like another project is brewing.....It definitely wont be a "bargraph" clock because that is too clunky to read. Maybe a fake gigantic nixie.

[Alex]

When testing IN-9 tubes a while back (I still have not actually built anything with them) I found them 100x better when used with unsmoothed rectified AC.... YMMV.

- Alex

[AlexTsekenis]

The only time i have experienced the glow not anchoring is when the anode voltage was not high enough to sustain the aux cathode glow. Worth looking into that.

A

[gregebert]

I did a quick-check with my IN-9 last night; here's a photo showing 2mA and 10mA. And as Alex suggested, it was with unfiltered DC (because I was too lazy to rummage around for a suitable capacitor). This was photographed in low-light conditions because the tube is quite dim. A string of 5 NE2H bulbs running at the same total current is much brighter.

[Dman777]

Wow, is the In-13 any brighter? And can the In-9 and In-13 be made to be as bright as a normal Nixie IN-12 tube(what I have to compare)?

Thanks,

-Darin

[gregebert]

You can usually get neon devices to glow brighter by pumping more current thru them, though it will shorten the lifetime. But in the case of a linear indicator like the IN-9, pumping more current thru it just makes more of it illuminate. You cant make a half-illuminated tube glow brighter. Even when the full length is illuminated, I didn't see much change in brightness when I cranked up the current. I seem to recall if I cranked a lot more current, say 20mA, it would start illuminating from the other end and started acting very strange, not to mention it was getting a lot warmer.

 I was able to get a very bright pink glow in the microwave oven for a split-second, and quickly turned it off before it exploded  or my wife found out. It will burn-up in a few seconds and I really dont want to do that...not yet at least. The only thing I would conceivably use it for would be a motion-activated night-light. It burns-up too much energy to be left on continuously. It looks really neat in darkness. Would be really cool to put a bunch in the front yard and have them flicker  randomly when someone walked-by at night.