6844A saga

[Paul Andrews]

Hi all,

I recently bought some 6844A tubes of ebay - I fancied making a four tube clock with round top-view tubes. In my head I had assumed that these would be doped with mercury, but they aren't. However, before I found that out I bought four Raytheon JAN 6844A tubes and 2 Burroughs 6844A tubes - I figured if I changed my mind and wanted to make a six tube clock, I might as well have the extra tubes lying around. Another assumption: They would have the same mechanical specs, but they actually look very different - I prefer the look of the Burroughs tubes.

All of them are NOS.

So, I tested them and the Raytheon tubes are fine. One had Cathode poisoning (NOS? It was in the original box!). That was easily fixed with some over current and it was fascinating to see that work - this is the first time I have had to do that.

The Burroughs tubes are quite a different story. On one of them, half the digits don't light up, but the leads to the digits do! I have posted some pictures below. On the other one, none of the digits light up - only the leads. Well, I'm going to put this down to experience - I am probably not going to build a clock with tubes that aren't doped with mercury - but I would like opinions as to what might be going on with the Burroughs tubes. Note that the behavior is independent of the actual anode current - other than how brightly they glow!

This one shows just the lead lighting up:

This shows the digit 3 and the lead lighting up:

This shows a lead and a 'not connected' pin lighting up:

This shows the digit 2 behaving itself!

[Dekatron42]

Raising the anode voltage has always cleared the problem with the wires glowing for me.

/Martin

[John Rehwinkel]

I don't know what's going on either, but the orange, pink and green glows simultaneously are wonderful! I kind of what that tube for myself now.

- John

[judg...@gmail.com]

The green is easy to reproduce. Just wear a fluorescent green running jersey when you look a the tubes!

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[gregebert]

I've seen this on 5031's; I was unable to cleanse them even with very high current (tube got very warm...)

 If you cant get the 6844's to clear-up, switch to 5092's. They are trouble-free; I have not had a single failure out of 24 tubes I've been running for the past 6 years.

[chuck richards]

I too have a rather long 6844A saga to tell!

Back in 2010 I built a 6844A clock. It works fine, the tubes are
fine. They do not have mercury, therefore the color is more
orange with no blue outline. This clock has a toggle switch on the
front
to shut off the readouts. I only run the tubes when I want to see
them,
otherwise they stay dark.

This clock keeps the best time of any of them.
It's a free-running clock, not connected to any time synching source
such
as WWVB or GPS. It holds up the correct time within about +/- 1
second per year.

The biggest problem I had with the 6844s was with the sockets.
There is a certain type of socket which very easily cracks the glass
from way too much sideways force on the pins. There is another type
of
socket which has much more supple forks which are mounted in nice
generous holes so they can move around to accommodate the pin
spacing. Found this all out the hard way after those "tube-killer"
sockets ruined (2) of my NOS 6844A tubes!!

At least my 6844a saga taught me the difference between real
sockets and cheap imitation junk sockets which are no good.

In my opinion, building a 6844A clock with the tubes mounted
in sockets out the front is well worth doing!

Chuck

>><https://lh3.googleusercontent.com/-z6PoJP4nnLg/WNPjcEjdM3I/AAAAAAAA
>AgM/ZNebX4kd688dm4tLHQctcx4gKlWhKQ4VQCLcB/s1600/IMG_1285.JPG>

>>
>>
>>This shows the digit 3 and the lead lighting up:
>>

>><https://lh3.googleusercontent.com/-FqBjwt1dVbQ/WNPjh-0kJoI/AAAAAAAA
>AgQ/Y3dHcwgftdcZzKl_Hdq-hV6CSKo_Pf9KQCLcB/s1600/IMG_1286.JPG>

>>
>>
>>This shows a lead and a 'not connected' pin lighting up:
>>

>><https://lh3.googleusercontent.com/-RxhpDHCFwfY/WNPjmNaOt7I/AAAAAAAA
>AgU/Qpm6i0ZEfQg2-FVLJq-dDXwgij2bSoSOwCLcB/s1600/IMG_1287.JPG>

>>
>>
>>This shows the digit 2 behaving itself!
>>

>><https://lh3.googleusercontent.com/-WsXz-S9LjuY/WNPjUwcZxiI/AAAAAAAA
>AgI/IqMWFM_bOCI8zIcgPCgBH98EAZQwRW_0gCLcB/s1600/IMG_1283.JPG>
>>
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[jb-electronics]

Personally, I am also a fan of the orange glow with no mercury :) Jens

[Paul Andrews]

Well this is fun! I upped the current signifcantly (6.9mA - just over 2x recommended max), which caused some internal arcing briefly! Blew a resistor (I guess it was a 1/4 W. Interestingly it went from being a 5.1K to being a 27K resistor).

Bottom line is it kinda sorta works. But the results are patchy and some of the wires still glow some.

The Raytheon's are much better engineered. All of the incoming gubbins is sprayed with something white - maybe an insulating coating - and the anode mesh has some kind of arrangement in the anode to let out the splatter. You can see some in the pictures below.

@Chuck, do you have a photo of the sockets you used? Though I was planning on just making my own.

@gregebert, I like the dome shape on the Burroughs 6844A tubes. The 5092 tubes are more like the Raytheons.

[Jeff Walton]

As the cathodes are “cleaned” by running at higher current, the problem with the wire glow may go away at regular current levels.  My understanding is that a 40-50 year old tube that has not been run may still end up with some mild impurities on the cathodes which will “burn off” after running for awhile.  Old tubes generally take a few moments to light reliably when first powered up.

 

The wire glow is sometimes impossible to fix, especially if there is no insulating coating layer on the wires.

 

Jeff

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[Paul Andrews]

Running them at a high currenr for a while has workee, except for one holdout. This digit will light at about 4mA, which is the maximum recommended. Occasionally it will light at 2mA. When it lights it pulls the same current as all the other digits, otherwise it draws less. So I am wondering if a constant current source might convince this recalcitrant digit to light. Or maybe I just want to play with a constant current source!

I've looked up a bunch of sources on the web (and here on this group!), but I really don't know enough to follow what is being said. I really need a circuit diagram, with specific parts and maybe some formulae I can slap in a spreadsheet if I need to adjust stuff. I get that there are drawbacks to simple solutions, but this is just to play around with. If anyone could help me out with this, I would be very grateful. In the meantime, I will keep plugging away with what I can find on the internet.