The Russians are correct! Early A-201 Polyatron prototype is shining blue!

[Dekatron42]

Hi,

I've just uploaded a very short movie showing my first tries at running an early prototype of the A-201 Polyatron, and it shines a clear blue, just as the Russians have said all along. https://www.youtube.com/watch?v=cUjeha4Tmeo

Unfortunately I have not tinkered too much with it so the driving conditions are not optimal, that's the reason for the short movie. I will spend some more time with it in the future to see if I can adjust the driving stage so it will run properly at higher speeds. Right now it looks like it is a simple adjustment of the screen/grid voltage.

I've included a few photos here that show it from a few different angles.

/Martin

[Dekatron42]

Well, I couldn't keep myself away from the Polyatron so I made a quick tweak of the pulse voltages as well as the screen/grid voltage, and voila it started to run somewhat better - now I have to go and take care of what I really should have done, household chores.....

https://www.youtube.com/watch?v=lZQVZ4pPC4U

/Martin

[gregebert]

Argon ? If so, I wonder if the decision was based it's abundance vs. Neon.

[Dekatron42]

Yes, probably, Kaganov - Каганов И.Л. Ионные приборы (Ionic Devices), says that early Polyatrons used 90% Argon and 10% Hydrogen.

/Martin

[Quixotic Nixotic]

I've occasionally wondered why we didn't see more nixie tubes on coin-operated equipment.

The German Tonomat Canteen Electronic II 160S jukebox has three tubes that scroll seductively while the carousel is turning. Otherwise the machine is a fairly ugly affair.

John S

[Quixotic Nixotic]

I understand that Dr. Timmy's Caffeinated Nixie tubes come in Cherry, Lemon/Lime, Fruit Punch, Watermelon, and Blue Raspberry.

John S

[Jeff Walton]

Yes!  But like many nixie tubes, these aren’t available anywhere either…

 

Jeff

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[Joe Croft]

Sweet!!

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[Mike Mitchell]

I considered using polytrons when I started the development of my Dekatron-based clock (shown here: https://www.youtube.com/watch?v=pK276xZWyo4 )

I was under the mistaken impression that the position of the glow couldn't be seen from the top of the polytron tube. Now after over a year of operation the zero cathode on the tens of hours is noticeably smaller. I don't know how much longer it will last.  I'm going to re-wire the tens of hours tube so that every other cathode is zero, the others one.  I'm hoping that the reset-to-zero circuit will still work when driving five cathodes instead of only one, and that the glow will move to one random "zero" cathode instead of all five. I wouldn't have had to worry about this if I'd used a polytron.

[Dekatron42]

When you say "the zero cathode on the tens of hours is noticeably smaller" do you mean that the glow is smaller or that the pin is physically smaller?

Can you take a photo of this "smaller" one and also of a normal one and show the difference?

/Martin

[Mike Mitchell]

The cathode has been eaten away. It is now shorter than the other cathodes. The glow is about the same.  I'll take photos tomorrow, the clock is at work.

[Dekatron42]

Ok!

I've never seen a pin become shorter over time but I haven't run my dekatrons for that long. Are you sure it wasn't short to begin with? The pins are quite uneven in length in some dekatrons that I have seen, even unused ones.

/Martin

[Mike Mitchell]

I just took a photo.  The zero cathode is at the top. The glow is on the one cathode.

[Dekatron42]

How much of the pins are glowing on your dekatrons? It looks like just the top portion is glowing on the first cathode in the photo. If only a small portion is glowing that will affect the wear of the pin. Also, what current are the cathodes run at? If a dekatron has been in storage for a long time, or if it has seen a lot of use the pins can be affected by cathode poisoning, they can be fixed by running them at high speed with a little bit higher current to get the shine to cover the pin fully. Some are hard to get to cover the pin fully but running them in the reverse direction (if possible) sometimes helps.

/Martin

[Mike Mitchell]

The camera flash washed out the glow. The glow covers a bit more than 1/2 the pin. I'm using A-101 dekatrons.

The power supply is a voltage tripler powered from the 120v mains. I have a 22-ohm fusible resistor in series with the main, then the voltage tripler. Each capacitor is 33uf, with a 6.8M bleed resistor in parallel. I don't remember the exact resultant voltage, but I think it was right around 500v. The anode current limiting resistor is 1M. That puts the cathode current at 0.380 ma to 0.325 ma, assuming the HV ranges between 510V and 495V and the tube's drop is between 130v and 170v.

I should be safe decreasing the anode resistor to 910K, but 820K would be too low. Next time I have the case open I'll measure the voltage drop across the anode resistor (and the power supply voltage).

[Mike Mitchell]

I got a chance to crack open the case today.

The supply voltage is 500v, the voltage at the anode is 162v. The voltage across the 1M current limiting resistor is 335v. The fluke 77's input impedence may have some affect in measuring the voltage across a 1% 1M resistor.

I tried adding a 1% 10M resistor in parallel with the 1M resistor. The voltage across the combination was 334v. I did notice the glow covered more of the pin.