B7971 "Repair"

[Jeff Walton]

Has anyone successfully "repaired" a B7971 where there is a mechanical short between two segments?  In this particular situation, a quick test of all segments looked like the tube was good but there is a short where the upper right diagonal and the upper right vertical segment have somehow overlapped at the top corner. The rest of the tube works as designed.  I'm not sure if this occurred in shipping or if it has been a long term problem.  The attached photos show the segments as best as I can get them so that you can see the place where it looks like the diagonal segment has gone over the top end of the vertical segment. 

As it is not a "whisker" that has grown between the segments, I'm thinking a mechanical shock might be the only way to separate them. 

 Suggestions for "repair" experiences are welcome!

[petehand]

I have. I had a similar problem and cured it by rapping the tube face down, hard, on a wooden board. The crossed segments sprung apart. I figured it must have been mechanical shock that crossed them to begin with so another shock might separate them. I'm not recommending it, just saying it worked for me. Of course there's a chance of breaking the tube, but you can't use it the way it is anyway. Strike it square so that a large surface area hits and you don't get stress concentrated on a small area.

[Kevin A.]

If I had to fix this, I would try taping the tube to a piece of wood and knocking the wood against a hard surface. This way you can still transmit a shock to the tube without directly smacking the glass.

[Jeff Walton]

It is such an unlikely way to fail that I think it must have come from a shock.  

For reference, this tube was shipped in the original Ultronics assembly and the other tube was broken.  The metal bracket holding the socket was bent and the broken tube was snapped at the base.  Photo attached. 

Thanks for the suggestion! 

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[Jeff Walton]

Great suggestion!  I like the way you think! 

Jeff

-------- Original message --------

From: "Kevin A." <ka...@scarletmail.rutgers.edu>

Date: 12/30/18 2:13 AM (GMT-06:00)

To: neonixie-l <neoni...@googlegroups.com>

Subject: [neonixie-l] B7971 "Repair"

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[Michail Wilson]

I have run into a few tubes like this.

 

I was lucky enough to have been able to dislodge them.

 

I believe you’re right in that it must have been in shipping as the seller of one of them actually took a video of the tube working and had lit each segment prior to shipping.

 

Similar to Pete’s and Kevin’s solution, I smacked the tubes against my sons hard cover math book (instead of wood).  I remember the first tube being very easy on the first hit.  The last tube was so hard that I remember giving in and thinking…. If I break it I break it. It eventually sprung loose as well.

 

Michail Wilson

206-920-6312

 

From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com] On Behalf Of petehand
Sent: Sunday, December 30, 2018 12:02 AM
To: neonixie-l
Subject: [neonixie-l] Re: B7971 "Repair"

 

I have. I had a similar problem and cured it by rapping the tube face down, hard, on a wooden board. The crossed segments sprung apart. I figured it must have been mechanical shock that crossed them to begin with so another shock might separate them. I'm not recommending it, just saying it worked for me. Of course there's a chance of breaking the tube, but you can't use it the way it is anyway. Strike it square so that a large surface area hits and you don't get stress concentrated on a small area.

On Saturday, December 29, 2018 at 11:26:16 PM UTC-8, Jeff Walton wrote:

Has anyone successfully "repaired" a B7971 where there is a mechanical short between two segments?

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[gregebert]

One of mine failed in this manner during normal operation. One segment is out and another pair of segments is shorted together. The first photo should display '30' (for today's date, Dec 30), and the second photo should be '9AM' (for 08:45:19AM).

I have yet to disassemble the clock and take measurements on this tube (very busy with NIMO project right now). When I do I pull the tube,  will find out how much resistance there is between the shorted segments, and decide if I want to zap it electrically like a fuse. Thumping and bumping of a 7971 wont be an option for me. Before these 8 tubes went into service, I generated I-V data plots for all of the segments so I can compare data afterwards to understand aging, etc.

[Dekatron42]

Be careful if you decide to zap it like a fuse, I have a few of these where people tried that and blew the connecting wire instead if the segments.

I just whack them against my palm and at an angle to dislodge them, has worked every time so far. I don’t dare to whack them against anything harder. Wearing a glove is recommended if you crack the glass.

/Martin

[Jeff Walton]

First, thank you to all that offered suggestions!  (Especially Pete Hand; Kevin A; and Michail Wilson)   Here is the tube and offending segments shorted together:

 

 

 

Please note:  I already tried whacking the tube on the palm of my hand and on the carpet until I thought I could not risk hitting it any harder.  Those attempts were unsuccessful.

So here is what I constructed based on comments to my original post:

 

 

Here is the result after five hard whacks on a carpeted floor with the tube taped to a ~1 meter piece of round dowel from a closet.  I kept one end in contact with the floor and rotated up and down to try to hit across the entire dowel surface.  The tube is wrapped about 10 times in wide masking tape.

 

Success!!!  I am amazed that the tube survived and this actually worked!!  Apparently there was enough shock in shipping to cause the overlap and enough shock when slapping the dowel and tube on the carpeted floor dislodged it!!!  The tube now functions on all segments and I’ve saved a piece of history and a bunch of money.  Thank you to the group for suggestions.

 

-Jeff