Lighting of only cathode lead wires

[Leroy Jones]

Hello,  A while back I was testing a batch of Burroughs 6844A nixie tubes.

None in the batch worked correctly.   Only the cathode lead wires glowed, not the

digits themselves.   I have noticed this repeatedly on Burroughs 6844A tubes.

However, usually when National NL-6844A tubes (NOS and in the red boxes)

are tested, they all work properly.

What causes the lead-wire glow problem?  And why does this happen

more often with the Burroughs version?

Thanks, Chuck

[David]

I have seen this also on these tubes. The 6844A is an early tube design that didn't have mercury added to prevent cathode poisoning. I doubt that anyone has done recent research on this phenomenon, so we're left with conjecture. Here's mine: after the cathode gets poisoned, the plasma has to be generated somewhere. That somewhere is the lead wires. Later tubes had insulating paint applied to the lead wires to prevent this. It's usually white or green.


David Forbes, Tucson AZ

> On Apr 26, 2024, at 7:29 PM, Leroy Jones <leroypu...@gmail.com> wrote:
>
> 

[Leroy Jones]

Hmm.   This thread somehow got deleted.   But anyway, as I was saying.....The National NL-6844A always tests better and with much more success than the Burroughs version ever does.

These are certainly NOT ideal tubes.  Short life.  No mercury.  But they do make up for their deficiencies by looking cool while they actually operate correctly.

Especially on a clock that has them mounted on a clear case, and sticking out the front.    -Chuck

[Leroy Jones]

Picture of clock built in 2010 that uses NL-6844A tubes.

[chuckrr]

Well the facts are that the National NL-6844A tubes always test much better than the Burroughs versions do.

I know they are not ideal tubes. No mercury. Limited lifetime. But they do look cool especially on a clock
that has them poking out the front.

Chuck

---- Original Message ----
From: "David" <nixie...@gmail.com>
Sent: 4/27/2024 11:35:58 AM
To: neoni...@googlegroups.com
Subject: X-IMail-SPAM-Connection Re: [neonixie-l] Lighting of only cathode lead wires

I have seen this also on these tubes. The 6844A is an early tube design that didn't have mercury added to prevent cathode poisoning. I doubt that anyone has done recent research on this phenomenon, so we're left with conjecture. Here's mine: after the cathode gets poisoned, the plasma has to be generated somewhere. That somewhere is the lead wires. Later tubes had insulating paint applied to the lead wires to prevent this. It's usually white or green.


David Forbes, Tucson AZ

> On Apr 26, 2024, at 7:29 PM, Leroy Jones <leroypu...@gmail.com> wrote:
>
> 
> Hello, A while back I was testing a batch of Burroughs 6844A nixie tubes.
> None in the batch worked correctly. Only the cathode lead wires glowed, not the
> digits themselves. I have noticed this repeatedly on Burroughs 6844A tubes.

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[gregebert]

I've tried depoisoning a few of these 6844/5031 tubes with zero success, even at high current (20+ mA). They get hot, but wont clean-up. Whatever contaminates the surface of the cathode is rather stubborn. Perhaps it's an oxide; many of these failing tubes have a black haze inside the tube, which I suspect is Iron(II) oxide. There is a lack of oxygen, so the familiar Iron(III) oxide wont form.