Bad B7971's

[Nicholas Stock]

Hi Folks...I have 5 B7971's here that have faults (i.e. multiple segments illuminated, missing segments)...and they're obviously of very little use in clocks. Any other uses for them out there? Anybody interested in them?

Cheers,

Nick

[jb-electronics]

Hi Nick,

sorry to hear that -- maybe you can send one do Dalibor for research / future inspiration?

Cheers
Jens

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[gregebert]

Measure the resistance between cathode pins to determine how 'shorted' they really are. It may be possible to zap the shorts. I've done this with IN-1's before. I'm more concerned about *how* they got shorted, because Burroughs tubes are legendary for their high quality.

Are the dead segments fully dead, or do they partially light ? Cathode poisoning comes to mind.

BTW, I'd like to obtain the 'worst' one you have for use as a museum-piece; private-message me the cost/details. Thanks.

[Nicholas Stock]

I took a look at the cathodes under a good magnifier and a few of them you can definitely see are physically overlapping in the center of the segments and no deal of smacking the tube can get them to move...;-( I'll PM you later today. I will measure the resistance of the less obvious ones too, thanks for the hint!

Cheers,

Nick

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[Mich...@aol.com]

Nick,

 

I have unfortunately been very lucky in getting bad tubes from ebay.  Probably have 20 or so now (broken, outgassed, missing segments).

 

I have taken the excessive risk in smacking them to get segments free of the ones that have overlapping and before and after pictures.  I think you will be surprised at how much impact the tubes can take before breaking.  That said, I have smacked them against my cupped hand to spread the impact point (not against a table).

 

I would say that I have recovered nearly all overlapping issue tubes.  Obviously, you have to look at the overlap and take an educated guess at the angle you want to hit (multiple times with increasing force until resolved). 

 

I do think in the years of tube smacking, I have only had one break in my hand.  Also, I have only made one tube bad in that the overlap dislodged; however, another segment stopped working (the connection from the circuit wire to the mica) and I can't even be sure the segment was not an issue prior to the smacking.

 

Michail Wilson
206-920-6312

[Mich...@aol.com]

Thought I would share, althought I might have already.

 

Last purchase on ebay was a sign which was made up of 7 tubes and says 'GO AWAY' or 'WELCOME' depending on the position of the switch. 6 more tubes were to come with it.

 

Well, I took video of opening the 2 boxes just because of experience with prior ebayers.  They were labeled from 1 - 13.  Well, there was only 12 tubes in the boxes (tube #12 was missing).  A slight resistance from the seller, but it was hard to dispute video of the opening and counting of the items.

 

Of the 12 tubes, 3 were overlapping and 1 had a bad segment.

 

Here are those 3 tubes:

https://www.dropbox.com/s/gkilytpol75hkpg/2015-12-05%2014.05.19-Mark.jpg

 

Also, a prior purchase of 6 tubes had 2 bad ones in it:

https://www.dropbox.com/s/lcuilr9axdssz1y/7971-Tube-Short.jpg

 

Michail

[Instrument Resources of America]

I've used this same 'smacking technique' to straighten up bent elements inside of such tubes, as Western Electric 'tennis ball' style of tubes where the glass support arbor is broken inside the tube. Have not broken one yet!!!   Ira.

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[Jeff Walton]

Michail,

 

Thanks for the explanation and photos of the 7971 tubes.  I have several that I will try to “repair” based on seeing what you have been able to fix.  There are some of the early 7971 tubes that use a thin rod to the top of the tube for support instead of the mica spacers and they may not respond too well to shock.  The later tubes (64 and later) which have partial or full mica spacers holding everything (top and bottom) should be fairly robust.  Have you noticed any more or less issues with the circuit board backplane vs the wire interconnect versions?

 

I also have a couple tubes with a dead segment where I can visually see an open wire from the pins to the segment.  Wasn’t thinking there was much of a market for them but maybe for someone building a clock where the tens-hours is either one or zero might be able to use them.  Much depends on the font that is being used.

 

 

Jeff

 

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[Nick]

Odd this. I bought substantial batches of these (in the several 100s) from the guy that originally owned pretty much the world's supply many years ago - apart from those that broke in transit due to very poor packing, I've never had a failure.

Where are all these different tubes coming from...?

[Jeff Walton]

I bought some from an eBay seller in the San Diego area about a year ago.   He offered me as many as I wanted at $110 each.   Claimed that he had "several hundred" available.  He was able to pick tubes that I requested (different types of internal construction) so I know he had a bunch to choose from.  Can't afford to buy many at that price but they keep showing up on ebay.. 

Jeff 

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[Mich...@aol.com]

For me, I buy them all from various people on ebay.

 

Seems strange that these tubes receive such an impact from shipping that they would cross over.   I think people are selling them on ebay knowing there is an issue with stuck segments already, but don't know about smacking them and so they sell as 'untested'.

 

There is/was a specific seller on ebay (he is still selling Nixie stuff) and about a third of the 40 tubes were flawed in this way.  I posted and video showing him.  He wanted me to file a claim stating they were damaged in shipping.  Not happy with this, I filed a claim with paypal instead and shipped them back to him.  Strangely, several days after getting them back, another seller (obviously a friend in the same area) had them up for auction.

 

Michail

[Mich...@aol.com]

Jeff,

 

Sorry, I have not taken notes as to which the tubes were, although I have both types.  I did look at some to see that the ones WITH the needle still have the mica spacers at the top.  So, you should still be fine smacking them around.

 

The tubes with the little space needle uses wire coming up from the bottom to the clips.  The ones without the needle have the type of circuit board going up to the clips.  I believe the last two tubes I was 'playing' with are disconnected at the clip to the element (not the circuit/wire to the clip).

 

I could take pictures when I get to work of various tubes if you're looking for something specific.

 

There is a market.  You can post on ebay as people still want them, but I highly suggest you be honest with an element being bad and light it up.

 

 

Michail

 

 

In a message dated 3/6/2016 1:47:41 P.M. Pacific Standard Time, jwalt...@gmail.com writes:

Michail,

 

Thanks for the explanation and photos of the 7971 tubes.  I have several that I will try to “repair” based on seeing what you have been able to fix.  There are some of the early 7971 tubes that use a thin rod to the top of the tube for support instead of the mica spacers and they may not respond too well to shock.  The later tubes (64 and later) which have partial or full mica spacers holding everything (top and bottom) should be fairly robust.  Have you noticed any more or less issues with the circuit board backplane vs the wire interconnect versions?

 

I also have a couple tubes with a dead segment where I can visually see an open wire from the pins to the segment.  Wasn’t thinking there was much of a market for them but maybe for someone building a clock where the tens-hours is either one or zero might be able to use them.  Much depends on the font that is being used.

 

 

Jeff

 

 

From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com]
Sent: Sunday, March 06, 2016 12:04 PM
To: neoni...@googlegroups.com
Subject: Re: [neonixie-l] Bad B7971's

 

Thought I would share, althought I might have already.

 

Last purchase on ebay was a sign which was made up of 7 tubes and says 'GO AWAY' or 'WELCOME' depending on the position of the switch. 6 more tubes were to come with it.

 

Well, I took video of opening the 2 boxes just because of experience with prior ebayers.  They were labeled from 1 - 13.  Well, there was only 12 tubes in the boxes (tube #12 was missing).  A slight resistance from the seller, but it was hard to dispute video of the opening and counting of the items.

 

Of the 12 tubes, 3 were overlapping and 1 had a bad segment.

 

Here are those 3 tubes:

https://www.dropbox.com/s/gkilytpol75hkpg/2015-12-05%2014.05.19-Mark.jpg

 

Also, a prior purchase of 6 tubes had 2 bad ones in it:

https://www.dropbox.com/s/lcuilr9axdssz1y/7971-Tube-Short.jpg

 

Michail

 

 

In a message dated 3/6/2016 9:15:19 A.M. Pacific Standard Time, nick...@gmail.com writes:

I took a look at the cathodes under a good magnifier and a few of them you can definitely see are physically overlapping in the center of the segments and no deal of smacking the tube can get them to move...;-( I'll PM you later today. I will measure the resistance of the less obvious ones too, thanks for the hint!

 

Cheers,

 

Nick

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[Jeff Walton]

I appreciate the sellers that post photos of the actual tubes operating.  

I've bought from postings without operating photos and in the past few years I have had about 10% with issues or poisoning of segments.  I've been able to bring back all of the poisoned segments but haven't tried to "fix" shorted segments. Not much can be done with opens.  

The tubes with the post (that I have) do not have mica spacers touching the glass at the top.  I'll dig them out and post a couple photos. 

Jeff 

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

[Instrument Resources of America]

Must be the same guy that I bought from. Each tube was wrapped up in a
single thin layer of newsprint, and then laid in the box side to side
against each other. And yes one did arrive broken, and he wouldn't do
anything about it. Ira.

[Mich...@aol.com]

Jeff,

 

Of the 30 or so tubes I have at home, only 4 have the post.  (I will check more when I get to work tomorrow.)

 

What I did notice is that not only did all 4 have the mica spacer at the top, but that all the other regular tubes have the spacer with the hole for the post pre-punched out.  Also, the tubes with the post stand about 4mm taller to account for the additional space needed for the post height.

 

Michail

[Jeff Walton]

Michail,

 

I should have been clearer about the mica spacer on the tubes with the posts.  I meant to say that the mica spacer did not support the tube inner assembly at the top.  I have attached some photos of the three main types of tubes I have seen:

 

Earliest tubes had the post but the mica spacers do not touch the glass at the top and the entire display assembly moves within the tube.  These seem to be from 1963 and earlier.  These used the wire interconnects instead of PCB backplane.  While there is a single protrusion of mica from each side, mine do not touch the glass and shaking the tube displays visible movement of the display assembly.  I would hesitate to strike these to fix a short because I would be fearful of breaking something else from the assembly movement.

 

Next version tube (Early 1964) eliminates the post and uses a full mica spacer that is in full contact around the inner circumference of the glass.  The examples I have are from the first half of 1964.  These used the wire interconnects instead of PCB backplane.

 

Later version (1965 -) uses a mica spacer that is only the width of the inner assembly and supports the tube assembly at the top in the same plane as the display using three standoffs on each side of the mica touching the glass.  These tubes all have the PCB backplane.

 

 

Jeff

 

From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com]
Sent: Sunday, March 06, 2016 7:19 PM
To: neoni...@googlegroups.com
Subject: Re: [neonixie-l] Bad B7971's

 

Jeff,

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[Mich...@aol.com]

Jeff,

 

I went through my entire inventory, and I don't have a single tube like the 2nd picture you posted (a mica at the top which is a circle).  All my tubes are like the other pictures which are 4 or 6 contact points.

 

So, I have been smacking silly the ones you were worried about.  I wouldn't worry about it.  Smack them around a little bit.

 

PS.  Now I gotta find more.  :)

 

Michail Wilson
206-920-6312

 

In a message dated 3/6/2016 6:45:24 P.M. Pacific Standard Time, jwalt...@gmail.com writes:

[Jeff Walton]

Michail, 

My tubes with posts only have one little standoff on each side that don't touch the glass.  Those are the ones that I hesitate to smack.  They seem to have made a number of changes to the construction during production.  

----

I have a clock that uses Raytheon CK8754 tubes that has 35 years continuous use with no tube issues.  That's over 300,000 hours.  I hope that the B7971's last as long.  I'll probably be gone by then.. 

Jeff 

-------- Original message --------
From: Michail1 via neonixie-l <neoni...@googlegroups.com>

Date: 3/7/2016 1:00 PM (GMT-08:00)
To: neoni...@googlegroups.com
Subject: Re: [neonixie-l] Bad B7971's

[jf...@my-deja.com]

On Monday, March 7, 2016 at 2:06:42 PM UTC-8, Jeff Walton wrote:

I have a clock that uses Raytheon CK8754 tubes that has 35 years continuous use with no tube issues.  That's over 300,000 hours.  I hope that the B7971's last as long.  I'll probably be gone by then.. 

Jeff 

I think I last posted about this more than five years ago.  A little more than 40 yers ago, I built three 6-digit clocks with B7971s.  They have been running 24/7/365.25, and there have been no tube failures, yet (one dead power transformer, some electrolytics, and one clock chip).  The tubes were cheap at the time (I think they were from John Meshna), so nothing was done in the design to extend their lifetime.  I also stocked up on spare tubes, and based on the current prices, I plan to use them to fund my retirement. 

[Nick]

I'm not surprised that some are showing mechanical damage - bearing in mind that pretty much all 7971s in circulation allegedly came from the same source (usmintquarters or something like that) and he was truly awful at packing them, even when shipping internationally,... I lost about 20 in transit from him. Enclosed is a photo some here will have seen before - this was from one batch of 100 (a box of 45 and a box of 55) - when I asked him to PLEASE pack them more carefully, rather than just in thin newspaper (the original single sheet that each was packed with when put into storage many many years ago) and in a pathetic cardboard box, his reply was that he didn't care and always packed a few more in the box to account for breakages,

It was tragic - 100s must have been lost and many more damaged this way...

Nick 

[Quixotic Nixotic]

Dear Nixiephiles,

I came across a french B7971 ad a while back on Ebay that claimed the tubes were all new and they were packed in an original styrene tray.

So this makes me ponder the following points:

1] They probably did not come from the usmintquarters source, as they were neatly packed in an original tray, not newspaper.

2] I have heard it said that the grey/gray around the cathodes shows that a tube is used and not in fact new. The reason for them being in an original styrene tray is presumably because the old tubes were put in the new tray after the tubes were swapped out, which brings me to point 3.

3] Has anyone ever seen a B7971 that does NOT have the grey around the cathodes, thus indicating that it is new? I have never seen a single example myself.

John S

[Marcin Adamski]

Hi John,

I have seen B7971s bearing signs of heavy use and other looking 'like
new'. They all have the gray fading and its extent seems not correlated
with the state of the tube. Personally I don't believe that the gray is
a sign of use.

Marcin

[Nick]

Hi John,

I remember these - we all discussed them a while back - ISTR that we couldn;t really decide if they were new or not - the consensus was, as you say, that they were probably pulls put back in the "new" trays - a lot of these seem to have been swapped at a set time, just in case - bearing in mind that they were mainly used in stock tickers, failure wasn't an option. The tubes are fine, and as many have found, they seem to go on for ever...

Nick 

[jf...@my-deja.com]

Back in the early 1970s, the cheap ones (~$1) all came with sockets with cutooff wires.  For about double the price, you could get the bracket with the HV driver transistors.  Clearly, these were used surplus from the NYSE.  It seems that they stayed cheap until the Nixie nostalgia hit the hobbyists in the 1990s.  I do not remember anyone since the 1970s claiming to have seen one come out of a sealed box.

 

On my tube that got broken, the substrate is a white ceramic, and it looks like there is a flat black coating of some kind.  In a brand new tube, I would expect either no shadowing (apply coasting before adding cathode wires) or much more crisply defined shadows.  To me, the wide and diffuse shadowing looks like erosion.  I think it would be kinda hard to deliberately manufacture in these shadows, and unless they are functional, it would not be worth the effort.

[Nick]

The tubes will have been burnt-in for some time after manufacture for QC checks... maybe that'd be enough to cause the shading?

Nick

[Jonathan F.]

Wow. A batch of 100 B7971 tubes...

I wish were alive the time these were cheap and easy to find..

I have only 5 of them, one has a bottom segmet that illuminate a orange cloud around it, possibly touching the grid or the back. I will try to smack it.

Btw... what kind of gasses were used in these tubes? At which pressure?

[Nick]

On Tuesday, 8 March 2016 17:21:10 UTC, Jonathan F. wrote:

I have only 5 of them, one has a bottom segmet that illuminate a orange cloud around it, possibly touching the grid or the back. I will try to smack it.

Btw... what kind of gasses were used in these tubes? At which pressure?

Neon with a small amount of Argon (maybe 5%) and possibly a trace of Mercury (nearly all later tubes have Hg doping - it almost eliminates sputtering and thus drastically improves the life of the tube). Pressure is between 5 & 30 Torr (about 1/25th of an atmosphere).

HTH

Nick  

[Jonathan F.]

I wonder how hard it would be to open up the tube maybe a 3mm Hole, and then try to move the segments with a wire, and reseal the tube.

just a thought.. but getting the right amount and type of glass in would be very difficult.

[Nick]

It's pretty much impossible to re-gas a nixie, not to mention being dangerous due to the Hg.

I tried doing this with an outgassed tube helped by a really expert hot-glass specialist.

We failed, probably on the annealing. The glass cracked.

Nick

[NeonJohn]

On 03/11/2016 05:56 PM, Nick wrote:
> It's pretty much impossible to re-gas a nixie, not to mention being
> dangerous due to the Hg.

There is no danger in the tiny amount of mercury involved.

>
> I tried doing this with an outgassed tube helped by a really expert
> hot-glass specialist.
>
> We failed, probably on the annealing. The glass cracked.

Probably a coefficient of expansion (COE) problem between the glass of
the nixie envelope and the tubulation you sealed onto it.

It is very likely that your expert glass specialist was used to working
with boro glass with a COE in the 10 range. Low power tubes usually use
leaded glass with a COE of around 90. more than about 5 points
difference and it WILL crack, regardless of the annealing.

The way to tell leaded glass is to look for dark and/or reflective
stains on the tubulation tip-off and around the pin header to envelope seal.

I've repaired a number of vacuum tubes and mercury rectifier but being a
neonist, I'm used to 90 COE leaded glass.

The way to determine the compatibility of two glasses is to take two
pieces (say, the tip-off bit left after diamond sawing the tubulation
tip-off from the bad nixie) of the glass and hold touching each other
with stainless needlenose pliers or hemostats. Place the pieces in the
fire and heat the tip of a glass rod compatible with the known glass.

When the glass has softened, touch the soft end of the glass rod to the
combo. Fire strongly and pull out to a fine thread. The known glass
will be on one side and the unknown on the other.

If the thread cools straight then the glasses are compatible. If the
thread curves away from the axis, then the glasses are not compatible.
The thread will curve toward the glass with the highest COE.

Sometimes a transition glass can be used. Uranium glass is a good
transition between leaded and harder glass. That's why you often see
bright green beads of glass around the pins of larger vacuum tubes.

Many high power vacuum tubes use boro glass for the envelope. There is
no good sealing glass compatible with boro up to vacuum tube standards
so U glass is used as a transition between the boro and the glass on the
pins.

I would not be at all hesitant to repair a Nixie, especially if I had
another one just like it that was scrap that I could use the envelope
glass to determine compatibility.

John



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[Jonathan F.]

Maybe there would be no need for glass at all, what if you would make a hole on the "stem" and then just reseal it with the original glass?

Maybe i will get a very bad 7971 one day and give it a try