Bad batch of Burroughs 6844A nixies

[chuckrr]

I would like to ask the group about an experience I am having with a batch of (8) Burroughs 6844A nixies just purchased.

They are new in box from 1968.  All have same date stamp Mar 4, 1968.   As far as I can tell they have never been out of

these original boxes.    I tested them and they all malfunction the same way.   The tiny wire leads inside the tube which

connect the digit cathodes to the pins get surrounded by a bright neon glow, and the digits never strike.  Once in a while

by connecting and reconnecting rapidly, I can get a digit to strike, but not often.

What is going on inside these tubes which causes this?   They were tested at 170 volts DC with 15k anode resistor.  Dropped that down

to 10k for a few tests, which helped a bit with some partial digits.   But this entire batch is bad.   What causes this?

The glow seems plenty bright.    Thanks,  Chuck

 

 

[gregebert]

Do these have dome-tops, or are they flat ?

I have several dead/near-dead Burroughs 5031 and 6844 nixies, which are the predecessor of the legendary 5092. All of them have dome-tops. I suspect that the 6844's you have might be the same construction as the 5031. I have a few of these myself, and no amount of high-voltage/high-current has been able to recover them. I concluded that they have leaked, rather than suffered from cathode poisoning. I have others that have sputtered, leaving a dark residue inside the glass, and a few with cathode-poisoning that just dont want to recover.

I dont know where you got them, but it wouldn't surprise me if they were sold as "untested".

Give one of them a trip thru the microwave oven and see what happens. I'm gonna do that to one of mine.

[chuckrr]

Burroughs 6844A is domed not flat.   I also have some National Electronics NL-6844A tubes.  Frankly, I have had much better

luck with the National Electronics brand.   This recently purchased batch of (8) Burroughs 6844A tubes is a bad batch.

The boxes all are stamped MAR 4 1968.  The tubes themselves are date-coded 6750 F20.  In white letters stenciled on the glass:

"Burroughs 6844A NIXIE".

 

The test I did was that the anode got connected to +170 volts DC through a 15k resistor.   Then the digit cathodes were selectively

grounded to the negative side of that power supply.    On all (8) of these Burroughs tubes, most of what is seen is an intense glow concentrated

around the tiny internal wires which connect the digit cathodes of the stack, to the pins.   These tiny wires pass closely to the outside of the

Anode casing which surrounds the digit stack.   The glow strikes in the wrong place.   The glow is around the lead wires instead of being

around the digits.    I am very confident from the way these tubes were in those boxes, that only one of the batch had even ever been out of the box.

 

So I am curious what causes the glowing lead wires.

 

Chuck

[gregebert]

I have not been able to figure that out for years. You would think the internal leads were coated with an insulator so they dont glow, or perhaps they use a different metal with a higher workfunction than the actual cathodes, so they would not glow in normal circumstances. But when the cathodes are still visible, I dont understand why they have no glow. I doubt they would be selectively plated with another metal, which completely sputtered away, leaving them unable to glow.

I have a bag of dead nixies, mostly 5031/6844,  took 2 out, and microwaved them for 2 seconds. Got a brilliant crimson glow. One of them shows some cathodes working, so now I have to go back thru the bag to make sure I find the totally dead ones, or at least the ones that have glowing only on the bondwires, and nuke them in the microwave oven. I have other boxes for dying nixies, and so-so nixies, so I'm really surprised anything in the "body-bag" of dead ones actually glowed. Unless perhaps the zap from the microwave oven did something to the internal metal.

I have some more experimenting to do.

[Paul Andrews]

I have about 12 6844A, all NOS, none of them work - they show the same symptoms that you described.

[gregebert]

Paul - Do any of your failed NOS units have a black or silvery coating inside the glass ? I'm hoping that is caused by sputtering, and not simple aging.

[chuckrr]

Thank you for the responses so far.  What interests mwe the most about all of this, is that this is making me wonder exactly what it is

that determines initially when the tube is brand new, the difference between the bond wires and the actual digit cathodes.   Upon close

examination of these dud tubes, and a known good working one, I can see no obvious difference between them.   Looking closely, I see that the

bond wires run very closely to the outside of the cylindrical shaped anode.  It makes perfect sense to me that these wires be surrounded with a neon

glow, simply because they are so close to the anode.  I want to know what the tube designers did to prevent this glow, and why it is happening now.

In other words, what exactly has happened to these tubes from sitting in their boxes since 1968, which would make the wires glow

now, yet they did not glow whehn the tubes left the factory.   Or possibly this was a defective batch that was never any good from day 1.

 

I suspect that they have leaked.  Something is probably up with the internal pressure, and/or the gas mixture.  Perhaps some air got in.

Not enough to completely kill it, but enough to cause this highly abnormal behavior.  I bet Dalibor might know.   Perhaps I'll contact him and attempt

to pick his brain a bit.  If anyone would know, he would.

 

I will say this much, however:   Looking back over the past 20+ years of  nixie tube collecting and use, I am concluding that

Burroughs 6844A tubes are often found bad for a variety of reasons.   Have had many scrounged up at hamfests, etc.  Lots of bad ones.

However, the National brand  NL-6844A tubes seem to have a much better chance of still being ok.

 

6844A turns out to be not such a great tube.   But I built a clock that has them prominently sticking out from the clear front

panel.   I have another clock in the works that uses 8422 tubes.   Those seem to be quite good as far as a high percentage of them

still being ok.  So my search for 6844A spares will continue.    I am now working with the Ebay seller of these (8) 6844A duds to

see if I can get back my $78 (ouch!) that I spent on them.  -Chuck

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[chuckrr]

@gregebert:    6844A is a non-mercury tube.   It has a relatively short lifespan, and yes, one of its properties is that

during use, the cathode material does get deposited on the glass.   They do silver up quite noticeably over several years of use.

They also get sputtered cathode material on the tiny ceramic separator washers in the cathode stack which eventually cause

multiple cathodes to glow when only a single cathode is grounded.   After the first ten years of operation in my 6844A clock, I recently

swapped out a tube that started having digits 7 and 8 on together.  Moved that to a location in the clock where only digits 0 through 5 are used.  - Chuck
 

---- Original Message ----
From: "gregebert" <greg...@hotmail.com>
Sent: 12/11/2020 9:47:35 AM
To: "neonixie-l" <neoni...@googlegroups.com>
Subject: [neonixie-l] Re: Bad batch of Burroughs 6844A nixies

Paul - Do any of your failed NOS units have a black or silvery coating inside the glass ? I'm hoping that is caused by sputtering, and not simple aging.
 

On Friday, December 11, 2020 at 6:32:45 AM UTC-8 Paul Andrews wrote:

I have about 12 6844A, all NOS, none of them work - they show the same symptoms that you described.

On Friday, December 11, 2020 at 1:45:30 AM UTC-5 gregebert wrote:

I have not been able to figure that out for years. You would think the internal leads were coated with an insulator so they dont glow, or perhaps they use a different metal with a higher workfunction than the actual cathodes, so they would not glow in normal circumstances. But when the cathodes are still visible, I dont understand why they have no glow. I doubt they would be selectively plated with another metal, which completely sputtered away, leaving them unable to glow.

 

I have a bag of dead nixies, mostly 5031/6844,  took 2 out, and microwaved them for 2 seconds. Got a brilliant crimson glow. One of them shows some cathodes working, so now I have to go back thru the bag to make sure I find the totally dead ones, or at least the ones that have glowing only on the bondwires, and nuke them in the microwave oven. I have other boxes for dying nixies, and so-so nixies, so I'm really surprised anything in the "body-bag" of dead ones actually glowed. Unless perhaps the zap from the microwave oven did something to the internal metal.

 

I have some more experimenting to do.
 

On Thursday, December 10, 2020 at 4:57:40 PM UTC-8 Chuck wrote:

Burroughs 6844A is domed not flat.   I also have some National Electronics NL-6844A tubes.  Frankly, I have had much better

luck with the National Electronics brand.   This recently purchased batch of (8) Burroughs 6844A tubes is a bad batch.

The boxes all are stamped MAR 4 1968.  The tubes themselves are date-coded 6750 F20.  In white letters stenciled on the glass:

"Burroughs 6844A NIXIE".

 

The test I did was that the anode got connected to +170 volts DC through a 15k resistor.   Then the digit cathodes were selectively

grounded to the negative side of that power supply.    On all (8) of these Burroughs tubes, most of what is seen is an intense glow concentrated

around the tiny internal wires which connect the digit cathodes of the stack, to the pins.   These tiny wires pass closely to the outside of the

Anode casing which surrounds the digit stack.   The glow strikes in the wrong place.   The glow is around the lead wires instead of being

around the digits.    I am very confident from the way these tubes were in those boxes, that only one of the batch had even ever been out of the box.

 

So I am curious what causes the glowing lead wires.

 

Chuck

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[Paul Andrews]

@Greg. They are all NOS NIB.

@Chuck. I like the domed tube too, but gave up ever trying to find any that worked. Like you, I am always more impressed with the National Electronics version of whatever Burroughs produced.

[chuckrr]

A few weeks ago I bought (2) NOS, NIB National NL-6844A nixies from an ebay seller.

When those arrived they got tested and both work perfectly.    -Chuck
 

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[chuckrr]

While I am on this subject, I figured it might not hurt to ask if anyone here in our group might have a few

fully functioning 6844A tubes available for sale.   Thanks.  -Chuck