Can Nixie Cathodes Become 'Poisoned' From Just Sitting?

[Tom Katt]

While working on my latest clock, I grabbed a few B5991 tubes from my stash that I assumed were unused new old stock - at least that's how I recall the description when I purchased them several years ago.  They look new (for what that's worth) - no signs of mirroring or other telltale sputtering marks and the glass doesn't appear to have a scratch on them - logos and markings intact etc.  But most of the digits failed to light under normal current and a few internal pin leads glowed rather than the cathodes.

I suspect this can only occur from use, or perhaps they were leaky?  I haven't run into this before with tubes that I haven't touched in decades.

I have managed to restore the first bad one by increasing the current and 'catching' the cathode illuminating without the lead wires.  Then I let them sit on that digit and increase the current to about 3ma.  Over the last few days, I seem to have the tube working pretty well and all the cathodes light properly with around 2ma or less.

I hope the rest follow - I've got 3 more in the same condition.

Thoughts?

[gregebert]

My vote is leakage. Enjoy them while you can. 

[Dekatron42]

There are some texts, it might have been from Burroughs, that mentions that Nixies that have been stored for a long time need some cycling of the digits for some time to light up properly, and this should also get rid of the bonding wires from the pins to the digits not loosing their glow.

I wish I had OCR'ed all documents and annotated them so things like this could be found easily - perhaps some AI-agent has done that for us!?

/Martin

[Oskar]

I have noticed a similar behavior in tubes that have not been used in decades. When first turned on, most cathodes wouldn't illuminate fully. Typically, the discharge would initially only occupy a small region of the cathode, slowly creeping its way around, probably "eating away" deposits of some sort. After this process has completed, the previously affected cathodes light up immediately.

[Nicholas Stock]

I see this quite often with the NL84x style tubes... the reticent cathodes soon come back to life though after some period of time. However, the Burroughs tubes can be a little bit more troublesome with the illumination of the lead wires.... this usually corrects itself after a while.

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[Jeff Walton]

I’ve seen this in more than one type of nixie and I always figured it was something that deposited on the cathodes over time.  Nixie tubes that have not been run in 50 years can do that.  Normal operation of running the nixies does cause material to be sacrificed from the surface of the cathode and if the envelope is fine and not suffering from gas leakage, the nixies that I have “rejuvenated” in the same manner as you seem to be just fine from that point forward.  It just takes a little patience to bring the current up until you get full glow from the digit without lighting up the lead wires.  After that, they seem to fire up normally.

 

Jeff

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[Tom Katt]

Thanks for all the replies!  I thought I was going a little crazy - I understand the sputtering deposits while operating, but I did not expect that to 'naturally' occur during storage.  But I guess it's possible that some kind of chemical movement is going on at a very slow pace when the tubes are not used for many years.  The restoration I'm doing seems to be working and they don't seem like leaky tubes I've had in the past (never try and push a B5991 / NL8422 into an IN-12 socket lol) - leaky tubes don't seem to have good and bad digits, they tend to be bad in general.

So this makes sense - I just found another 2 tubes, so now I have a full set of 6 ;-)

Tom

[Leroy Jones]

I have a clock I built here in year 2010 that uses (6) of the 6844A tubes.    Burroughs is B6844 sometimes with A sometimes not.   National is NL-6844A.

I have had horribly bad luck with ALL Burroughs B6844 tubes.   Absolutely NONE of them have EVER worked right at all.   Mostly the lead wires glow and that is all I get no matter how I cycle the

current, voltage, even trying it backwards with + going to digits and - to anode plate/screen.    I had some bit of luck with some old military B6844 tubes where I made up an elaborate switching circuit

that makes the digits on both sides of the desired digit, to be the anode.    That makes them light up.  All digits too.   Real good.   But that circuit is an absolute complex nightmare and would be no good except

as a wild idea to test.       To get real 6844 tubes, get NOS in box National Electronics (the red boxes), NL-6844A tubes.    Those just WORK.   Period!  No messing around they just come directly to life with no horsing around of

 ANY KIND whatsoever.       In fact, ALL National nixie tubes in general have in my observations done over the past 40 years, been of consistently high quality and high reliability.   Gentlemen:  It all really boils down to this

for me:   If the part number does not have "NL" in front of it, I am not very interested in that tube.    The exception to that rule is Burroughs B-7971.  Those all seem to work very well.   But for most anything else it should be National.

Just sharing my real life experiences with y'all.   -Chuck

[Tomasz Kowalczyk]

I also confirm that I've encountered this with tubes purchased as "NOS, untested". Some digits did not want to light up, connection lighting instead, but after "borrowing" the discharge from another lit digit they started behaving normally, lighting up the digit rather than connection when powered from nothing too. 
Partial discharge also healed within minutes of being operated at regular current. It is not the true cathode poisoning which doesn't go away so easily, just a thin deposit of something. 

[Tom Katt]

Now that you mention it - most of my other tubes were National NL8422.  The Burroughs B5991's were in the same box and I historically have considered them equivalent tubes.  But I have never had issues like this with the National tubes - these Burroughs are the first to be problematic despite likely being unused old stock.

Strikes me a bit ironic - wasn't Burroughs the 'inventor' and copyright holder of the Nixie naming?  You'd think they'd be the better tubes lol.

On Wednesday, August 5, 2026 at 12:25:58 AM UTC-4 Leroy Jones wrote:

in fact, ALL National nixie tubes in general have in my observations done over the past 40 years, been of consistently high quality and high reliability.   Gentlemen:  It all really boils down to this

[Dekatron42]

Are the date codes in the same range on Burroughs and National Nixies or are some later than the others? I'm thinking that production could have changed over the years that makes some more prone to problems.

[Tom Katt]

All my tubes herald from the early 1970's...  I think the National tubes are '73 and '74 while the Burroughs are stamped 1972.  I wouldn't think that one year would make a difference, but perhaps there were some design revisions made by NL...

[Jeff Walton]

I have not had any particular issues with the quality of Burroughs nixies.  In fact, I have a clock running with all Burroughs 5991/8422 labeled tubes that has been running for years with no issues and I really like that tube.  I’ve still got (24) of the 5991/8422 tubes and (20) of them are Burroughs branded.  Some of them appear to be used but when I fire up the tester, all of them light up normally without pushing them.  I’ve never gotten any 5991/8422 in original boxes.  I’ve had far more issues with NOS 84x series nixies (some in original boxes) needing to be “woken up” from long storage. 

 

There is some evidence that after Burroughs and National stopped making tubes, there was a lot of late-date unwanted inventory throughout the supply chain which may have been re-branded or marked.   LEDs caused such a sudden shift in the need for production quantity nixies that a lot of later U.S. production ended up without any market for the product, so strange things may have happened with unwanted inventory.  The U.S. had nowhere near as much over-production as with USSR nixies, which continued to be produced long after the demand ceased.  I recall reading somewhere (on the forum?) about U.S. tubes that may have actually been made by Burroughs which were rebranded in various blue and black markings as NL-XXXX tubes.  I think that most of the Burroughs original markings were a white color.  My Burroughs 5991/8422 tubes range between 1969 and 1973 date codes.  It would be interesting to know actual market share numbers for Burroughs and National.

 

Others may have had different experiences with certain kinds of Burroughs nixies, but based on the performance of the B7971 tubes that are out there, Burroughs made some really reliable tubes.  Overall, I have found more National branded tubes of different varieties in the wild and I am happy to get either them or Burroughs.   

 

Jeff

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[gregebert]

The only Burroughs tube I've had problems with are the 5031, which was an early generation that probably lacked mercury and I dont think it used a Penning mixture. I have several that only have glowing bondwires and no amount of high-current rejuvenation attempts has had any success.

The 6091 has been reasonably reliable, though nothing like the legendary 5092.

[Leroy Jones]

Yeah, glowing lead wires is what I have experienced on ALL Burroughs B6844 tubes.    Have tried many from Ebay.   Tested.  Only lead wires glow.  Got full refunds each time.

 Now I will not even bother with them any more.    -Chuck