Introduction & Telefunken Varisymbol alphanumeric advertisement sign ZM1350 ZM1360 & ZM1370

[Magnedyne]

Well, this serves as my introduction and and as a thread about a beautiful sign I just picked up.

Firstly something about myself.

I’m a 17 year old collector and (hobby) historian of vintage computers, my interests are mainly minis, mainframes, early micros and kit/diy computers. But I’ve got a few other different bits and bobs throughout the history of technology as well.

Now back to the reason I joined this group. 

I came across an absolutely beautiful Telefunken advertising sign for the, frankly underdocumented, Telefunken Varisymbol tubes. They were Telefunkens response to the Burroughs 7971 alphanumerical tubes. These were only sold for a very brief amount of time and exclusively in Europe. 

Interestingly these are flat like panaplex tubes and the anode is not a grid, but a coating on the inside of the tube. These are the earliest gas discharge tubes, well the ones I’m aware of anyhow, which used such a coating. 

The sign is a handmade one off which was lugged around to fairs to advertise the Varisymbol to potential Customers. It implements all three sizes of the Varisymbol ZM1350 ZM1360 & ZM1370. It can alternate between „TELEFUNKEN“ and „VARISYMBOL“ at four different speeds. Switching between the sign reading „TELEFUNKEN“  three times, then „VARISYMBOL“ three times and the sign reading „TELEFUNKEN VARISYMBOL TELEFUNKEN“/ „VARISYMBOL TELEFUNKEN VARISYMBOL“  is possible as well. Unfortunately three tubes don’t display quite properly. I’m hoping it’s just the electronics, I haven’t had time for a detailed diagnosis yet. Even if it’s the tubes, it seems to be the most common type at least, the ZM1350 which seems to have popped up most often in the past.

Any further info about the Varisymbol is greatly appreciated.

Cheers,

Magnedyne

[Nicholas Stock]

WHAT A FIND!!! OMG. I didn't even know there were smaller versions of the ZM1350 (shame on me!).

The tubes with the partially lit segments can probably be revived with a little extra current... just be careful not to burn them during the healing process (if it works..).

Wow..

Welcome to the group,

Nick

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[Magnedyne]

Indeed amazing. And for just 100€. I absolutely adore one off / small batch internal stuff like this. Together with  my intellec 8 and pieces from a computer from Konrad Zuse definitely amongst the best stuff in my collection.

[Magnedyne]

From what I understand there is some deposit on tubes which show this symptom. Increasing the current can burn said deposit off allowing current to flow and resulting in the nixie glowing properly again. Should I just build a power supply with which I can increase the current or is there simply a resistor wired in series acting as a current limiter? What shows me that the current is high enough? How long does it take and when am I done? I’m guessing that the result will be visible by the tube glowing properly again but better safe than sorry.

Nicholas Stock schrieb am Montag, 13. November 2023 um 21:56:10 UTC+1:

[Magnedyne]

Furthermore I should mention that the partial glow does not affect only specific elements of the tube but any element inside the tube. 

Can this be caused by deposits?

Nicholas Stock schrieb am Montag, 13. November 2023 um 21:56:10 UTC+1:

[Terry S]

Awesome sign! Would like to see the circuitry.

[Nicholas Stock]

Oh, it moves? Probably a leaky tube then I'm afraid.. unless anybody else on the list has ideas?

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[Audrey]

Bad connection somewhere possibly, wouldnt surprise me if the tubes are socketed

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[Paul Andrews]

An amazing find. I have some ZM1370, I've never seen any ZM1360. You can find some documentation here https://www.nixies.us/bwg_gallery/zm1370/.

BTW Nick, the ZM1360 is bigger than the ZM1350 at 60mm high.

[Nicholas Stock]

Really? How did I not know about these? My wallet does not need any more distractions..... LOL.

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[Paul Andrews]

Because all the segments are in the same plane, it is possible that they could all get deposits equally, so increasing the current may work. Yes, the current is controlled by a resistor. The documentation I linked you to gives the recommended current for each segment. To try to re-condition the segments I would double the current, but I would only do that with the affected tubes.

These tubes are known for having a low yield so it is possible that the affected tubes have other problems, such as outgassing. I would be very careful when removing them from any socket they may be in to avoid breaking a seal between the pin and the tube.

[Kevin A.]

Wow this is an exciting find! Yes, I would certainly use a high voltage supply with fine current adjustment to try un-poisoning the partial glowing cathodes. 

Cheap way would be to get a low cost PSU such as NCH6300HV and get a large variable resistor (rheostat), perhaps one up to 20K with a few watts rating. You can then lower resistance when powered and see effect of increasing current. Might also he good to have a dmm or other current meter in series to monitor.

This display would make an awesome retrofit project for a ESP32ish WiFi capable controller with clock, custom message functions, weather, etc. As much as I appreciate originality, you could keep the look original but make it a full featured unit with internet, synced time, cross fading and other cool effects, dimming and PIR sensors (to save tube life), etc... just thinking out loud. 

[Magnedyne]

I'll definitely keep it original as all the circuits inside are beautifully hand made, and to a high standard at that. Whilst it would be a cool project, in my opinion this would be sacrilegious. This is a one off piece of history I'll never get back if I replace the internals. After all I know nobody with a nixie advertising sign of any sort.

[Magnedyne]

I’ll take pictures as soon as home from school today. ~ 14:30 CET.

[Magnedyne]

No it doesn’t move whilst the tube is on but if different elements inside the tube are on they show  the exact same symptom.

[Magnedyne]

Alright, thanks for the tips. I’ll see what I can do. Not doubling the current on other tubes should be obvious, if anything ill modify the circuit on those to run on like 60% current or something, don’t want those to wear out after all. How long would I double the current on the affected tubes? I’m guessing until it lights up entirely, but what if it doesn’t? I don’t want to risk damaging any tubes further unless I have access to a replacement. Interesting regarding the yield, where did you find that info?

[Magnedyne]

You might just be correct. According to the seller this sign sat in a damp basement for the better part of fourth years which could easily result in corrosion on some of the sockets. Furthermore taking a look at the pictures in the listing it seems that whilst these three tubes were noticable, they weren't quite as bad as they are now. Fingers crossed it's just a bad connection.

[Magnedyne]

This sign was most likely built in the former Telefunken Röhrenfarbrik in Ulm, Germany. I picked it up closeby as well. Luckily I live close to Ulm because I wouldn’t have risked shipping such a delicate sign.

[Richard Scales]

Awesome find - very well done.

I am seriously envious!

I look forward to seeing how you get on.

- Richard

[Paul Andrews]

Regarding the yield? Just my (and others) experience with 'new old stock' tubes. I don't have any information on what the yield was at the time of manufacture. Its easy to rationalize a low yield because of the large seal between the glass and the body, but that would just be guesswork.

Interesting that the affected tubes were better in the original photos. In the U.S. we have a product called 'deoxit' that is used to fix old electrical contacts that may have some dirt/corrosion on them. It is just sprayed on the contacts and then the device is used as normal, though I don't know what the breakdown voltage is of the product. I have used it in old vacuum tube devices.

[Magnedyne]

I have opened it up and removed all of the crumbling foam it was filled with. Lucky me, it wasn't foam which turned to goop.

Well, the tubes are not socketed, instead they're directly soldered in. So definitely not corrosion. Seems like it's the tubes.

[Paul Andrews]

Might be worth checking some voltages - bearing in mind that those voltages are likely to be lethal if they short through you. If you've never done that kind of thing you should be very cautious. You should have an isolation transformer and plug the sign in to that.

Power supplies can deteriorate over time, specifically the capacitors dry out if they aren't used and the voltage becomes unstable, given that these tubes worked better just before you bought this, it is making me wonder if this is a problem you are having. If you have an oscilloscope, that would be better than a multimeter so you can see if any mains frequency is making it through. You could probably figure out what the voltage should be by checking the resistors on each cathode and comparing them with those on the datasheet I posted a link to. There is a good chance that the tubes are being multiplexed, which would mean that the resistors would typically be lower for a given anode voltage.

Can you post some close-ups of the circuit board, transformer and part of the wiring loom?

[J Forbes]

really neat! it would be interesting to see a close up pic of the circuit board, so we could read the numbers on the components, and see when it was made....

[Paul Andrews]

I should also say that the anode voltage might be full-wave rectified. Life is not simple.

[Terry S]

Let it run continuously for several days, it may clear up on it's own.

[Magnedyne]

I’m somewhat experienced with proper high voltage stuff and know what precautions to take. But yes it’s always good to tell people these things, not everyone is aware after all. Yeah, I planned on replacing the capacitors anyways at some point, preemptive maintenance is always good. My Intellec 8 is waiting on some new caps as well. I’ll pull out one of my scopes some time this week and take a look. I was planning on reverse engineering the whole thing as well and creating schematics, this would make Troubleshooting in the future a lot easier. Another thing I’ve wanted to check is the voltages, might be running a little high since a couple decades ago the grid voltage was increased from 220 to 230V, which should be still within the tolerance of +-10 but I’d rather check. Since I was planning on reducing current anyways reverse engineering would be a good first step. I’ll post the schematics when I’m done.

[Magnedyne]

I’ve uploaded some pictures, the sn47123 has got 7222a written on it, that would put the display no earlier than the 22nd week of ˋ72. I was not aware these tubes were released this late. Now granted the ic doesn’t have to be original, might’ve been replaced at some point. The rest of the components would date the display a bit earlier in my opinion as well, I’d guess late 60s. On the other hand Telefunken probably just would’ve used what they had laying around. So likely this display was actually made sometime in the early 70s. Alright, enough for today gotta really head to bed.

[Magnedyne]

[Magnedyne]

[Magnedyne]

[Magnedyne]

Magnedyne schrieb am Mittwoch, 15. November 2023 um 08:34:47 UTC+1:

[Alex]

Nice Find.

Looking at those pics it seems clear to my eye that this has cathode resistors rather than anode, one for each used cathode. These will then likely be in three groups, Telefunken only, Varisign only and common to both. This then yields one anode wire to all (red wire?)

 And three cathode wires (three blacks). It does look like they have only put tails on used cathodes.

Circuit is likely a simple astable / flip flop with a pair of big transistors for switching the cathodes, maybe with a variable amount of capacitance on its base for the fade effect?

I would suggest an apprentice build back then, maybe the mechanics are nice but I would say the electronics are fairly hum-drum.

My approach with this would be to remove the resistor strips, add missing cathode wires, make up some ruler like PCBs with serial HV latches on and replace the main veroboard with a PCB with your favourite micro / embedded solution. This can take in / use the original switches and transformer so with the back on it would look the same. You can then keep the bits removed for archive or if there is enough space, mount new bits on top as a mezzanine. Depends on your goals really, but as is it's more of a curio / collector asset only really...

It would blow their minds back then to have scrolling dynamically updated text, and would make use of all the segments (assuming those have not been poisoned to oblivion with deposits).

For your current segment poisoning, you could parallel another fairly high R resistor across the existing ones for that tube to up the drive. Certainly no multiplexing going on here!

Are you certain they are not socketed? Looks odd with the wires disappearing into the material like that.

Best of luck!

- Alex

On Wednesday, 15 November 2023 at 07:34:47 UTC Magnedyne wrote:

[Magnedyne]

I'll probably leave it as is. I find the curiosity/historical aspect to be more interesting and important than having something which has a use. It's just like the homemade computerkits I collect, each tells their own little story. Some are unfinished, who knows for what reason maybe something got in the way, somebody lost motivation or something else entirely. I wouldn't even think about finishing these kits just to have a functional computer, it's more interesting this way.

Yes I'm certain the tubes are not socketed. The baseplate has holes drilled in it which the leads poke through. The unused leads have been bent to the side so that the tube stays in place. I'm uncertain if glue has been used. The wires are soldered to the pins directly.

For now I'll keep it running for some time, like Terry suggested, maybe the tubes will come back on their own but I certainly doubt it.

[J Forbes]

Thank you for the pictures. It's a fascinating device!

[Terry S]

I agree, don't change a wire! It's a piece of history as-is. Fix any defects and let it live as a tribute to the original designer. Who are you (or any of us) to second guess the designer? Could you update it with an Arduino and make it do back flips?  Yes of course But should you? No.

[Paul Andrews]

Regarding ZM1370 - I literally posted a link to my photos of one earlier in a reply to your initial post.

On Nov 24, 2023, at 6:59 PM, Magnedyne <Miro.S...@airgrips.de> wrote:

Alright I’ve done some more research and it appears that this sign might even more special than I previously thought. Some have claimed that Telefunken never sold the ZM1360 and ZM1370 due to them turning out not economically viable. The datasheet for the Varisymbol mentioned datasheets for the ZM1360 and 70 being worked on. I have furthermore found no documentation regarding the ZM1360 and ZM1370 ever being commercially sold. Now of course a lack of documentation is in no way proof but I’ve also not been able to find anyone, or even pictures for that manner, of these two tube types. 

If this were to be true I’d have pre production, or rather sample tubes as production never happened. I’m very glad that none of these seemingly nonexistent tubes are „defective“/have a coating.

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[Magnedyne]

Gosh, I totally missed that, sorry. I had opened the link but missed that it was about the 1370

[Nicholas Stock]

Wow.

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