EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: marekpasek on December 01, 2017, 07:46:13 pm
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Hi, recently I am playing around with some nixies. when I applied 170v though 20k resistor. It lit up but around expected orange glow, some kind of purple halo appeared. I thought it is caused by overcurrent so I tried few other resistors (39k, 82k, 150k) and I varied voltages between 150v and 200v. The purple halo is still here. So is it normal? Is there supposed to be any purple halo? Am I not shortening the lifespan of the tube?
Thanks
About the picture: you can see the halo I am talking about the best on the top of number 3.
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from what i've seen the blueeypurpley haze in the tubes is just the bit of mercury they put in there to prolong the cathode life. more common in newer tubes than older ones.
sometimes LOWERING the cathode voltage can make this glow worse. make sure the voltage and current of your supply is properly spec'd for your particular tube. you want the mercury to vaporize and dissipate in the tube, not hang around. (if you know what I mean)
sometimes even just running the tube for a while will allow this to dissipate and become less obvious.
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That sounds logical. I bought these tubes as new so the tube was running for a minute at most when I took a photo.
Thanks
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Some types of glass fluoresce a blue colour, when exposed to UV, so perhaps that's what may be going on here?
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The haze is ionized mercury vapor, most US made Nixie tubes have them, especially those designed with multiplexed drive in mind. Personally I think it looks cool, but you can put a red/orange filter in front of the tubes or coat them with lacquer if you wish to block it.
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A Nixie is an old fashioned vacuum tube (valve). 55 years ago my vacuum tube audio amplifier had tubes that glowed purple because their plate and screen voltage was higher than normal and they needed replacement every 3 months.
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The Mercury doping is there to extend the operating life (ong life tubes). I think it's the former Soviet era IN-1 (end-reading, socketed) tube that is known for early failiures due to lack of doping. I've seen reports of them failing quickly due to inter-cathode shorts across the spacers from accelerated spluttering.
Your blue glow is a good thing.
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A Nixie is an old fashioned vacuum tube (valve). 55 years ago my vacuum tube audio amplifier had tubes that glowed purple because their plate and screen voltage was higher than normal and they needed replacement every 3 months.
No. A Nixie is a gas filled tube, containing a mixture of neon, argon and mercury.
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All appliances I have with neon indicator lights need the neon lights replaced after a few years. How long does a Nixie tube last when turned on continuously?
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According to my Mullard databook Nixie section, life can be as little as 3000hr (ZM1040, single digit illuminated continuously), the same tube is >20,000hr with digits changing at least every 100hr. At the other end of the spectrum, for a long life tube (ZM1000) it quotes >100,000hr (digits changing at least every 1000hr) at rated current. I'm sure dropping the current a bit would improve on this.
The end of life is normally taken as the point where cathode poisoning causes incomplete digit illumination. I think there are techniques (short term over-drive spluttering?) that can partially reverse this. Continuous long term illumination of a single digit causes poisoning of adjacent non-illuminated digits (cathodes).
As I said for the Soviet ones it can vary between models, a few are troublesome, the IN-1 being the worst (I think) due to inter-cathode short formation. Gas composition and Hg doping can make a big difference.
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Lifespan is also highly dependent on drive current. If you run the tube at half rated current, it will appear much more than half as bright and will last many times longer.