7971 nixie tube problem

[Clarke Payne]

I have run across some 7971s I have had stored for 30 yrs. 3 of the 12 glass envelopes fractured when I picked them up. One just disengrated.others seemed good cleaned up ok havent tested yet but appear to be in sound shape. Anyone run into this problem. Any special precautions before I test them?

[Nicholas Stock]

Fractured when you picked them up? Odd. Have they been exposed to long periods of temperature swings in storage? That might make them susceptible. Nothing special with regard testing them. Easy check for gas is to hold them next to a plasma globe....be careful if you need to bend the pins, be gentle as you can fracture the glass if you're a bit ham fisted (ask me how I know....). I presume you have a good device to test them with....

Best of luck! They're lovely tubes...

Nick

Sent from my iPhone

> On Sep 7, 2017, at 09:22, Clarke Payne <clark...@gmail.com> wrote:
>
> I have run across some 7971s I have had stored for 30 yrs. 3 of the 12 glass envelopes fractured when I picked them up. One just disengrated.others seemed good cleaned up ok havent tested yet but appear to be in sound shape. Anyone run into this problem. Any special precautions before I test them?
>

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[gregebert]

I had none in storage, and the ones I purchased in the past year had no signs of stress. Is it possible yours were damaged in storage ? I've never seen glass weaken on it's own. Also, the pins are fairly rigid (unlike IN-18's which are quite soft) so if there are any bent ones, it suggests the tube was stressed while stored.

I suggest you carefully inspect the base for glass-cracks, then bench-test them. If you are into data-collection, I suggest gathering I-V data for each segment on each tube, then plotting and comparing. It takes a bit of time, but I'm glad I did it for mine.

[Clarke Payne]

as far as I can tell temperature changes were not "radical".  packed in solid thick plastic case with no stress. tube pins look straight. will check with magnifying glass. ones that broke when I picked them up developed hairline cracks immediately.  one just disengrated. when I get home will post pics and on the others will do a comparison of segments. Thank you guys for your input. will do some more investigation. the only other thing that may be remarkable is the broken ones have no markings. the unbroken ones have the Burroughs b-7971 stamp.

Clarke

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On Sep 7, 2017 1:07 PM, "gregebert" <greg...@hotmail.com> wrote:

I had none in storage, and the ones I purchased in the past year had no signs of stress. Is it possible yours were damaged in storage ? I've never seen glass weaken on it's own. Also, the pins are fairly rigid (unlike IN-18's which are quite soft) so if there are any bent ones, it suggests the tube was stressed while stored.

I suggest you carefully inspect the base for glass-cracks, then bench-test them. If you are into data-collection, I suggest gathering I-V data for each segment on each tube, then plotting and comparing. It takes a bit of time, but I'm glad I did it for mine.

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[Tomasz Kowalczyk]

What do you mean by "disintegrated"? Did it break into thousands of pieces, like a car window?

W dniu czwartek, 7 września 2017 19:32:45 UTC+2 użytkownik Clarke Payne napisał:

as far as I can tell temperature changes were not "radical".  packed in solid thick plastic case with no stress. tube pins look straight. will check with magnifying glass. ones that broke when I picked them up developed hairline cracks immediately.  one just disengrated. when I get home will post pics and on the others will do a comparison of segments. Thank you guys for your input. will do some more investigation. the only other thing that may be remarkable is the broken ones have no markings. the unbroken ones have the Burroughs b-7971 stamp.

Clarke

Sent from Verizon Note 2
   

On Sep 7, 2017 1:07 PM, "gregebert" <greg...@hotmail.com> wrote:

I had none in storage, and the ones I purchased in the past year had no signs of stress. Is it possible yours were damaged in storage ? I've never seen glass weaken on it's own. Also, the pins are fairly rigid (unlike IN-18's which are quite soft) so if there are any bent ones, it suggests the tube was stressed while stored.

I suggest you carefully inspect the base for glass-cracks, then bench-test them. If you are into data-collection, I suggest gathering I-V data for each segment on each tube, then plotting and comparing. It takes a bit of time, but I'm glad I did it for mine.

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[Clarke Payne]

Yes one like a car window only with no glue. The other 2 developed hairline cracks when picked up.  Ira will check further when I get back home. May be knock offs but who would have made them?

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[Terry S]

Just curious -- were they stored with exposure to anything that might cause pin corrosion -- thinking out loud here... Maybe that caused stress on the glass.

Terry

[Tomasz Kowalczyk]

The glass needs to have high tension in it to break like that. This is interesting, I've broken few tubes in my life and they all crack like standard glass (big pieces and small amount of small shards). 
Combining this with fact that the breaking ones had no marking leads me to a crazy idea - maybe these were samples meant to have higher endurance and that's why there was tension introduced into the glass on purpose, just like in car windows? Toughened glass can take harder hits from the outside. 

It seems they weren't more durable on the long run. 

[gregebert]

I was thinking thermal-cycling; if they were stored in a garage or attic for 30 years where temperature is unregulated, it could cause a lot of thermal cycles. Imagine if there was something like a clothes-dryer, furnace, or water-heater nearby; they would cause a lot of thermal cycles over 30 years. These are large tubes, so they will be more vulnerable than smaller tubes.

Next on my list would be vibration; if the tubes rattled inside their box, or against eachother, it could weaken them.

I dont know of any house-hold chemical that would attack the glass itself; Hydrofluoric acid is the only substance I know of that etches glass.

[Jeff Walton]

Wow, that's really odd - and really bad luck. My original B7971 tubes survived 40 years in moving boxes from home to home with no real special protection and have worked well after being put into a clock about 3 years ago. I can't understand what would cause the glass to do this in a regular environment.

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[Nicholas Stock]

Speaking of B7971 tubes...

http://www.ebay.com/itm/good-burroughs-b-7971-nixie-tubes-qty-available-/232480774966

I have a hunch I know where these came from and how much was paid for them too.....but that's irrelevant. 30 tubes for sale though!

Not my auction etc etc...

Cheers,

Nick

On Thu, Sep 7, 2017 at 3:10 PM, Jeff Walton <jwalt...@gmail.com> wrote:

Wow, that's really odd - and really bad luck.  My original B7971 tubes survived 40 years in moving boxes from home to home with no real special protection and have worked well after being put into a clock about 3 years ago.  I can't understand what would cause the glass to do this in a regular environment.

-----Original Message-----
From: neoni...@googlegroups.com [mailto:neonixie-l@googlegroups.com] On Behalf Of Clarke Payne
Sent: Thursday, September 7, 2017 11:23 AM
To: neonixie-l
Subject: [neonixie-l] 7971 nixie tube problem

I have run across some 7971s I have had stored for 30 yrs. 3 of the 12 glass envelopes fractured when I picked them up. One just disengrated.others seemed good cleaned up ok havent tested yet but appear to be in sound shape. Anyone run into this problem. Any special precautions before I test them?

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[Paul Andrews]

The same seller has an empty school display board for sale that takes 15 of those tubes, so he picked up two of them?

There is also this clock with six tubes in it that I am surprised is still for sale: https://www.ebay.com/itm/122680353656

(Sorry, don't mean to hijack this thread)

[Terry S]

That vintage clock is interesting indeed. Built from a 1976 article in 73 magazine. You can read part of the article. The author discusses the voltage rating of the transistors, notes that he has no data ... and "inquiries among friends and on the nets failed" ....

On the nets? Was that perhaps ham radio lingo in the 70's? Or was he portending the future?

Also, he paid $5 for the 6 nixies and the driver boards.....

Terry

[Robert L]

Complete 73 issue from July 76... See here:

https://ia902601.us.archive.org/31/items/73-magazine-1976-07/07_July_1976.pdf

Caution... thread drift... 

Found the clock in the attached image on the local Craig's List back in April... Seller and I each traveled a couple of hours to meet at the farthest North BART station. Fun day... 

Rotary switch on the back of the clock has three positions... "fast forward", "slow forward", and "keep time". Time is derived from the 60 Hz line frequency. Could well be the same circuit from 73 Magazine. Can't bring myself to harvest the tubes!

73 de Bob

[Tomasz Kowalczyk]

That's an interesting method of driving the anodes. 

[gregebert]

Most of my clocks use non-isolated AC-line voltage for the anode supply; as long as you follow good design and safety practices, you will end up with a reliable and more-efficient design compared to DCDC converters and transformers.

It's very important to have properly-sized fuses, PCB traces, and wiring. Also, proper spacing, insulation, and warning labels (Hopefully my clocks will outlive me and someone will be taking care of them in the next century). Lastly, filtering from AC-line spikes and surge-protection.

My first nixie clock has 4000-series CMOS gates tied to the AC line, and they have worked flawlessly for years. This was a design challenge I had wanted to do for many years; I knew it was theoretically possible but I had to prove it for myself. There are several stages of filtering, so the logic gates never see any of the ugliness that exists on the AC line at the wall-outlet.

There are billions of devices that have circuitry running on the AC line without transformer protection; think of LED and CFL bulbs, and the input-side of laptop/cellphone power adapters. Not to mention the older tube-based radio/stereo/TV sets with hot-chassis. And most of these have UL, CE, etc recognition.

-----------------------------------------------

Thanks for posting the 73 magazine; there's a certain magic about electronics from that era that doesn't exist anymore. Part of it is that you could touch, feel, and understand just about anything electronic back then. Not true today.

[Mitch]

The clock uses an MM5314 in a multiplex configuration. That was ok when the tubes cost $2.50 each. I’d probably keep the clock in one piece, but long term it’s probably a good idea to replace the electronics with a direct drive circuit if running it full time.

[rmp]

I built one of these back in the early '70's. As I recall, it kept poor time, I suspect from noise in the power line getting into the clock chip. At the time, I lost interest and disposed of it. Grrr!
Anyway, when an old-timer ham refers to "nets" he's referring to "On-Air" chat groups, not "On-Line".

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

I built three clocks inspired by this article,  but I used the CT-7001 instead of the MM5314.
The clocks have been running continuously, and after 35-40 years there have been zero
Nixie failures.  There only component failures have been one power transformer,  one filter
capacitor, and one clock chip(!).

I also built LED clocks based on the MM5314, and they ran fast (which I attributed to counting
noise pulses on the power line).  The CT-7001 has an internal oscillator, and I think they try to
phase-lock it to the power line: some of the clocks ran slightly fast, and some were slightly slow,
and I believe that it was due to tolerances in the RC setting the MUX frequency.

The B-7971's do sing and produce RFI at the MUX rate of about 2 kHZ, and this would be
eliminated by using direct drive. If you believe that direct drive will increase the life of the tubes,
I do not believe that will be true.  I think I paid $1 for each tube+socket from John Meshna, and
my most expensive components were the HV PNPs from PolyPaks.