# Nixie tube resistor calculation

Discussion in 'The Projects Forum' started by Rocky_circuits, Dec 7, 2011.

1. ### Rocky_circuits Thread Starter Member

Nov 1, 2011
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Hello! Haven't seen me in a while, recently been furiously workin away at the clock. I have gotten the clock portion of the circuit working! Hurray! Thanks to your guys's help

So now the Nixie tubes are in as well as the 74141 chips to drive them. I also have built my high voltage power supply. So other than piecing things together, I need to calculate the resistor needed for my nixie tubes.

That talks about a little bit of a different problem though.
Using the calculator here, or basically just using ohms law, I find using a 180v to power the tube at 170v I need a 4k resistor.. That doesn't seem right, usually nixies are using like 10k-40k though right? Hmm..

I also noticed that after igniting the tube could stay on even at 135v where as it states minimum is 170.

But anyway, I want to figure out how to properly do it. If I have exactly 180v coming from my power supply, what resistor do I need on each anode? Or how can I find out

2. ### magnet18 Senior Member

Dec 22, 2010
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It's tricky, it doesn't use the striking voltage.
You need to calculate using the voltage it will be running at, since before the tube lights, the current is zero, and the voltage drop across the resistor is zero. After it lights, it runs at 150 (or, as you noticed, 135). Fun properties of gas tubes.
This means that you actually need to drop like 60 volts with the resistor, (Maybe 30, if your tube actually runs at 150V) so you'll need a 24K or a 15K, try 24K first and measure the current, if it's too low try a 15-17K

[EDIT]
Yea, finally beat wookie and bill to a helpful post!!

3. ### Rocky_circuits Thread Starter Member

Nov 1, 2011
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Righteous! I'll take it to the lab so I can better measure the current draw. In the meanatime I hooked it all up starting at 135v and a 10k resistor. Seems to work but definately need to find at what voltage I have my nominal current. I have one test tube so this testing im not worried about hurting the tube to much.

I also found it wasn't working totally right at first, however it turns out I was a dumb dumb and forgot that my logic is inverted. Soo close, I can taste it! Only one new problem to sort out, just a little programming though that's all

Thanks for the help magnet18, i'll be back with pictures and video of the final project completed next week!

4. ### Wendy Moderator

Mar 24, 2008
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The mod giveth, the mod taketh, the mod eraseth as if it never existeth.

I'm looking forward to it. While I have worked on HP equipement with nixie tube I've never worked with them up front.

5. ### magnet18 Senior Member

Dec 22, 2010
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You may or may not have misunderstood me, you still need 180V attached to the resistor, and when the tube lights, current starts flowing, and the resistor does it's job.

Good luck!

Dec 26, 2010
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The ignition voltage and the minimal anode voltage are both given as 170V. If the voltage is any less than this, starting may be unreliable or may deteriorate with use. The nominal supply voltage should be adhered to, as Magnet 18 says. Remember to increase the resistor before increasing the input voltage.

Unless you use much too low a resistor, or exceed the maximum supply voltage, you should not damage the tube quickly: a few seconds at maximum current will do no harm. Obviously you will want to check the current as soon as power is applied, and switch off promptly if it seems too big.

7. ### SgtWookie Expert

Jul 17, 2007
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On a related note; do a Google search on "cathode poisoning".
One in the list:
http://www.tube-tester.com/sites/nixie/different/cathode poisoning/cathode-poisoning.htm

That one is strictly related to Nixie tube cathode poisoning.
The last note on the page mentions how to avoid the poisoning; spin through all the numbers like a slot machine on a regular basis. This would be easy to do on a microcontroller; not so easy using discrete logic ICs.

8. ### magnet18 Senior Member

Dec 22, 2010
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IIRC, you can also run the tube backwards once it has occurred, though I would check on that before trying it.

9. ### Rocky_circuits Thread Starter Member

Nov 1, 2011
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Oh yes I know, I was just curious to the fact that it still lit with the lower voltage. I do wish to do it correctly though so i'll be running the 180v
@sgtwookie, I remember you talking about that before. In fact I already found that one of my 4's was slightly poisoned and used that method to clean it up

I was thinking of having my logic circuit as a secondary clock basically. For class points really. I have already programmed a microcontroller to count in binary and works wonders, not to mention it has so many possibilities! although I did it backwards so I need to reverse that otherwise my 74141 chip recieves the opposite input than it should. And can add a button for the slot machine affect.

10. ### magnet18 Senior Member

Dec 22, 2010
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Well then, best of luck, be sure to post some pictures when you get it done!!