Lighting all digits at the same time: Why does this happen?

[Yohan Park]

I have a few Chinese QS30-1 tubes lying around which don't have much value for me and was wondering how it would look to have all digits lit at the same time.
So I looked up the specs which say 170V and 2.25mA
So I calculated the needed resistor to have it hooked up to 230V which is a little below 27K
I then connected a 27K resistor to one cathode and it lit perfectly fine (230V AC so the anode also glows).
So I then connected 10x 27K resistors to all the cathodes and plugged it in.
Holy Moly! The thing lit up like crazy and was drawing over 9 Watts and was getting VERY hot. So I turned it off again after a few seconds.
Can anyone tell why it's behaving like that?

[Bill van Dijk]

Just a guess, but I think by lighting them all up you get some kind of “super ionization” in the tube, which could then increase the current and heat dissipation.

 

Bill

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[gregebert]

Very interesting; thanks for posting.

You might want to try successive numbers of lit cathodes, say 01, then 012, then 0123, etc and see how the current increases, and also see if it changes over time due to heating.

I dont recall seeing this behavior with segmented tubes, like the 7971. In fact, on my clock I have a current regulator on each cathode, and another one for the anode, for every tube.....that works out to 128 current regulators on that clock.

[Paul Andrews]

You should calculate the anode resistor you need for one segment. Use that, then connect all the cathodes to ground. I have done this many times accidentally.  Now the hand waving part: Imagine the connection between the anode and cathode is a resistor and you connect all of the cathodes together - you are putting all of those resistors in parallel. You are limiting the current on each one to 2.25mA, so you are pumping 22.5mA through the one tube. I get that to be about 2W - (230-140)*0.0225.

[Jon]

You're putting AC across the tube? In addition to what Paul said, think about the scenario in the negative half-cycles. There you've got ten 'anodes' (the display digits, normally cathodes) each with their own resistor pouring current through one 'cathode' (the normal anode box/grid), which is definitely not sized for that current flow nor designed to have the glow on it bombarding its surface with lots of energetic particles. So all bets are off on tube behaviour in my view.

In either polarity of the cycle,  the common electrode might be seeing 22.5mA through it if your initial calculation holds. But very likely it doesn't, because that calculation assumes the normal tube maintaining voltage which I would have no confidence in being the case under these conditions. If the maintaining voltage drops significantly when the tube is run like this, then your current flow will be even more than you calculate. Maybe that's how you get to 9W.

Ouch. Wouldn't bother putting that tube in a clock!

Jon.

[David Pye]

Surely you've effectively got 10 of those resistors in parallel so the tube current is 10x rated....

Poor old anode....

David

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[严泽远]

There're over 17 different versions of Chinese QS30-1 tubes (SZ1-1, SZ3-1, SZ-8 are all same with QS30-1 but different brands), just curious which one you tested.

Check the pictures here: https://www.nixieclock.org/?page_id=3162

[Yohan Park]

Oh that's a great website! Thanks for posting the link.
The tube I tested is the SZ3-1

[David Pye]

Please tell me there is a huge warehouse in China that will start selling their stocks to bring the worldwide Nixie prices back down again!

David

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[Yohan Park]

Prices will never go down.
I bought some cheap tubes from TaoBao years ago (the SZ3-1 I started this post with and I think I paid $0.50 or so) but Chinese tubes are now expensive as well.
Buy what you can buy now without looking at prices from 10 years ago.
What you have will only increase in value because there's going to be less available every passing year.

[严泽远]

There was a huge warehouse in China, but now it's running out. The price of QS30-1 is around 2RMB 10 years ago, but now it's near 30RMB/pcs

[Nicholas Stock]

Yan, were any of the QS30-1's or other Chinese tubes doped with Hg?

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[严泽远]

Hi Nick, I have never seen any Chinese Nixie tubes doped with Hg, I am also curious why, maybe it's limited by the level of technology at that time in China.