Geissler tube with a contact problem - Page 1
Forum section: electronics / repair

author: Physikfan
author_rank: Regular Contributor
timestamp: December 25, 2017, 10:54:05 am
content: To all friends of antique Geissler tubesThe picture shows a complex shaped Geissler tube.Unfortunately, the corresponding metal cap with eyelet is missing during a contact.Please, does anyone know how to fix this problem?Best regardsPhysikfan

author: jpanhalt
author_rank: Super Contributor
timestamp: December 25, 2017, 11:36:46 am
content: If there is enough sticking out,just attach to it. Can't tell from your picture. If not, how hot does the electrode get? I'm thinking of a very low-temp alloy or the newer, solderable conductive ink that is pure silver with no organic matrix.Finally, repairing that one bulb by a half-decent scientific glassblower would be easy, if the glass can be reworked. Do you know the gas and pressure in the tube?

author: Gyro
author_rank: Super Contributor
timestamp: December 25, 2017, 01:58:22 pm
content: That's a beautiful Geissler tube, I haven't seen one like that before.It would be good if you could post a close-up photo of the damaged end. The internal pressure is very low, so it would collapse during any attempt at glass blowing.Luckily the current it needs to pass is very low and the voltage required will happily ignore any resistive connection. Your main challenge is to obtain a replacement matching end-cap which is a good match for the other one. It ought to be possible to fabricate something from some thin brass tube or sheet.For the actual connection, if there is any wire still protruding, I would wrap this with some very fine wire to make the connection and make it secure with a little adhesive. I wouldn't risk soldering that close to the glass, you would possibly damage the seal or crack the glass. You could them form a bundle or pad of wire which will make contact with the replacement end-cap when fitted (or maybe run down the side under the cap). secure the new cap to the glass with something like epoxy glue.If the lead-out wire is completely gone, then you will have to resort to conductive paint (rear screen repair type) to make the connection.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 25, 2017, 02:14:55 pm
content: @GyroI think you misunderstood my comment. Any half-competent glassblower would know to release the vacuum before working on the glass. Cutting off an electrode like that and replacing it is really quite easy. Then of course, you need to re-evacuate the device and seal it.

author: Physikfan
author_rank: Regular Contributor
timestamp: December 25, 2017, 04:09:53 pm
content: The tube is at least over 100 years old.A glass blower should have available the same kindof glass for a successful restoration of the tube.Is there an electrical conductive glue available to make a connection without applyingmechanical stress to the tube?Also it may not an easy task to find such a new metalcap.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 25, 2017, 05:27:50 pm
content: Here's a link to the conductive ink I mentioned. It is a variation of the Tollens reagent/reacton:http://pubs.acs.org/doi/abs/10.1021/ja209267cThe reactants are volatile, so reasonably thick conductors of pure silver are possible. It is reported to be solderable.I copied the recipe years ago. If you want to go in that direction, I can post it here.EDIT: I have also seen prepared "ink" for sale in small amounts. Just search for silver ink +the lead author. That might be more reasonable than making it yourself, if you have limited experience in chemistry. However, Tollens reaction is one of the first things taught in many laboratory courses. It is very robust and hard to screw up.

author: Gyro
author_rank: Super Contributor
timestamp: December 25, 2017, 05:48:51 pm
content: Quote from: jpanhalt on December 25, 2017, 02:14:55 pmSorry, yes of course you are right, I should have said more of what I was thinking. The problem with unsealing the tube is achieving the same pressure and gas composition as the original. Manufacture of these things was, the time, an art rather than a precise science. The it may have been just been a relatively poor vacuum with residual air (mainly nitrogen), or it may have had proportions of various Noble gasses. Nothing so pure as would be achieved today in gas discharge tubes and signage. As the OP says , it is an antique and getting it back to the authentic composition and pressure could be difficult.

author: Gyro
author_rank: Super Contributor
timestamp: December 25, 2017, 06:04:02 pm
content: Quote from: Physikfan on December 25, 2017, 04:09:53 pmI really would still be tempted to try to fabricate a new cap, using some very thin sheet brass (or tube if you can find a matching diameter). Use a wooden mandrel of the same diameter as the glass, shape it and solder the seam together, bend in at the top and do the same and add a wire loop for external connection. It would be a visible repair, but an 'honest' repair. Maybe you can make a conductive 'pad' of scrunched up fine wire to make a light pressure contact between the end of the tube and the cap. The cap could then be glued to the sides of the tube using a ring of compliant rubber type adhesive that would minimise stress on the glass, but could later be removed with solvent if a more 'professional' repair becomes available. Silver loaded epoxy would probably also work, but the result would be a lot more permanent.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 25, 2017, 06:13:32 pm
content: I agree, my first approach would be to salvage what is there. A small spring might come in handy for the contact. Epoxy has become the duct tape adhesive solution, but consider glyptal (a heavy enamel), which would be more vintage-appropriate as an adhesive.

author: Gyro
author_rank: Super Contributor
timestamp: December 25, 2017, 06:19:17 pm
content: Yes, when I said Silver loaded epoxy would be "a lot more permanent", I should probably have added 'too permanent' compared to a solvent based adhesives.

author: oldway
author_rank: Super Contributor
timestamp: December 25, 2017, 08:03:24 pm
content: Spray GRAPHIT 33 where the metal cap with eyelet was placed, this will make a conductive coating on the glass.(KONTACT CHEMIE)https://www.amazon.fr/KONTAKT-CHEMIE-conducteur-graphite-GRAPHIT/dp/B002ZXQY9QProtect other places with insulating tape so you will have a conductive coating only where it is needed.After drying the conductive coating, remove the insulating tape.Wrap a thin non insulated copper wire on the conductive coating and glue it.

author: SeanB
author_rank: Super Contributor
timestamp: December 25, 2017, 10:56:39 pm
content: Most of the caps are cemented on, so a simple cement loaded with graphite powder will make a good enough contact material at the current that these tubes draws. The contact material has to be able to survive high temperature, as the terminals dissipate most of the energy used in the tube.

author: KE5FX
author_rank: Super Contributor
timestamp: December 26, 2017, 12:06:14 am
content: You really only need one connected electrode with a Geissler tube, because the counterpoise is capacitively coupled to the environment anyway. A couple of centimeters of aquadag or metallic ink should be OK as a contact at the unenergized end, with a meter or so of wire hanging off of it.

author: Physikfan
author_rank: Regular Contributor
timestamp: December 29, 2017, 07:27:36 pm
content: I hope to have found a usable electrically conductive adhesive nowto solve the problem with the one contact (missing metal cap with eyelet).

author: Cyberdragon
author_rank: Super Contributor
timestamp: December 29, 2017, 09:09:48 pm
content: Ahem...allow me to take a quote from the product packaging.QuoteMake of that what you will...

author: Ian.M
author_rank: Super Contributor
timestamp: December 29, 2017, 09:24:11 pm
content: Also, will it take the heat?IMHO the best option would be the conductive paint used for car window demister repair to extend the contact from the broken-off pin to the sides of the glass seal, then fabricate a brass cap as Gyro has previously suggested from shim stock, except don't solder the side seam or more than half the end seam, and form it round a smaller diameter mandrel so it grips the sides of the seal by its springyness to make reliable contact with the conductive paint.

author: Physikfan
author_rank: Regular Contributor
timestamp: December 29, 2017, 09:52:54 pm
content: Unfortunately there are more problems:Contact with cap:Contact without cap:

author: jpanhalt
author_rank: Super Contributor
timestamp: December 29, 2017, 10:09:56 pm
content: If there is any portion of the electrode sticking though the glass, and I can't imagine a situation where that is not true, why not use a spring to contact the stub. The current is very small.You also need to think of whether an action is reversible. Now you need to deal with removal of the epoxy. In this case, that should not be too hard.

author: Ian.M
author_rank: Super Contributor
timestamp: December 29, 2017, 10:14:20 pm
content: Now we can see the problem better. A sprung contact mounted on the glass isn't going to work unless its much much bigger than the other cap as there aren't any parallel sides on the seal for it to grip.I can see why you want to use conductive glue, but for %DEITY%'s sake stay away from Epoxy - use something that can be removed by soaking in an aggressive solvent.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 29, 2017, 10:33:00 pm
content: I disagree. It is a glass-metal seal. That means there has to be metal to which a spring can make contact.

author: Cyberdragon
author_rank: Super Contributor
timestamp: December 29, 2017, 10:39:37 pm
content: Wait, what is going on here?There looks to be an inner part of the electrode on the broken end, but not on the end with the metal part. However, there looks to be a metal rod in that evacuation tube on that end. Is that part of the other electrode that broke off and fell in there? If that is, it'sand you'll need a glassblower to fix it. I would assume the metal rod is not only to provide more surface area for the arc to form, but to keep it away from the seal.

author: jpanhalt
author_rank: Super Contributor
timestamp: December 29, 2017, 11:06:41 pm
content: Sorry, it was half-time and I needed to fix dinner. On further thought...Do you have a high-voltage, high-frequency source like a Tesla coil, a neon light transformer with a spark gap, or even a diathermy machine?My thinking is this. Whatever broke the electrode may have affected the glass-to-metal seal. The tube may be at atmospheric pressure (or close), and won't work regardless of what you do.As one responder said earlier, if the tube itself is OK, only a single electrode is needed (hence the Tesla coil test).If the tube doesn't light with a Tesla coil, the tube is bad. You need on-site help to fix it. It is a wonderful piece of history, and I would hate to see it destroyed by someone with no experience.John

author: Neomys Sapiens
author_rank: Super Contributor
timestamp: December 29, 2017, 11:27:36 pm
content: There is a guy in Germany who is refurbishing Geissler tubes and has a lot of info about them. I might did it out but you'll certainly find it when you search for 'Geissler Röhren'.

author: Physikfan
author_rank: Regular Contributor
timestamp: December 31, 2017, 06:01:57 pm
content: Hi jpanhalt, Gyro, oldway, SeanB, KE5FX, Ian.M, Cyberdragon and Neomys SapiensI have followed your suggestions and have provisionally treated the electrode without cap with conductive silver.The tube is working, the operating voltage is about 13 kV.Best regardsPhysikfan

author: Physikfan
author_rank: Regular Contributor
timestamp: January 02, 2018, 09:03:42 am
content: One question remains:Which gas makes this white discharge?RegardsPhysikfan

author: Gyro
author_rank: Super Contributor
timestamp: January 02, 2018, 10:58:42 am
content: There are specific gases that produce a white discharge, eg. Argon. But in this case I suspect that it is imperfectly evacuated air (it needs to be imperfect, otherwise it would be virtually impossible to get a Geissler tube to discharge).A natural atmospheric combination of mostly Nitrogen (pinkish white to bluish white depending on current density), Oxygen (a bit of Violet/Lavender), CO2 (again, bluish white to pink) and other trace gasses do combine to something whitish at the right pressure. The Automatic White Balance of your camera is probably influencing what we see versus what you see too.As I mentioned previously, internal pressure was a fairly critical 'trial and error' factor in getting early Geissler tubes to produce a decent light.... and that's a decent light!

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 02, 2018, 05:59:15 pm
content: It's probably Krypton.

author: Physikfan
author_rank: Regular Contributor
timestamp: January 03, 2018, 10:00:46 pm
content: In a catalog for physical demonstration devices from 1909 I found onesimilar Geissler tube:

author: Gyro
author_rank: Super Contributor
timestamp: January 03, 2018, 10:11:18 pm
content: Time to polish up your woodturning skills! The original base would probably have been Ebony, or possibly Mahogany.Then find a nice safe display case for it.

author: jpanhalt
author_rank: Super Contributor
timestamp: January 03, 2018, 10:18:29 pm
content: Beautiful. I had the privilege of attending an old university that had unexplored and seemingly forgotten tunnels that had been used for storage beneath the usual basement-level tunnels. I took home several similar antiques. Unfortunately, our babysitter/house keeper years later didn't understand the significance of one of the artifacts from the late 19th century, and she broke it.Don't make that mistake with your find!John

author: Bashstreet
author_rank: Frequent Contributor
timestamp: January 03, 2018, 10:32:21 pm
content: What a nice tube and the skill to make one... 1909..

author: james_s
author_rank: Super Contributor
timestamp: January 04, 2018, 02:02:21 am
content: Wow, that's the most amazing Geissler tube I've ever seen.Looks like you already figured it out but there are various carbon loaded glues and paints that are plenty conductive for this. I just recently found a small jar of carbon paint sold for shielding electric guitars and used it to replace the flaking aquadag on an old CRT, it worked just fine.Carbon dioxide produces a white discharge and was used in some early gas discharge tubes. IIRC it eventually breaks down into carbon monoxide, I don't know whether it will eventually recombine.

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 04, 2018, 02:52:28 am
content: I don't think it's CO2. CO2 and CO are both blueish, where this seems a more pure white. It's probably argon or krypton. But, of course, the color of gas discharges can depend on contamination, voltage and pressure too. And it's possible the camara could be affecting the color. The only way to be sure is to get a spectral reading. You could just use a visual spectrometer (is that what the little plasic tubes with the thin plastic prisms are called?) and compare the pattern to known gasses.

author: james_s
author_rank: Super Contributor
timestamp: January 04, 2018, 06:25:20 am
content: It's virtually certain that the camera is affecting the color, it's hard to say precisely how though.I've had an old soft seal helium-neon laser tube turn white, the bore discharge that is, it had completely stopped producing any coherent light long before. I have played with relatively high pressure CO2 in a home made discharge tube and it was bright white. This was at a relatively high pressure compared to most discharge tubes though.

author: Physikfan
author_rank: Regular Contributor
timestamp: January 07, 2018, 12:26:26 am
content: These are the first, just with reflection grating and camera primitively recorded grating spectra of the Geissler tube:The second green line of the first spectrum is also in the second spectrum as the middle line and in the third spectrumincluded as the leftmost line.The question is now:Which gas coresponds to these spectra.Best regardsPhysikfan

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 07, 2018, 01:52:21 am
content: Argon?

author: Physikfan
author_rank: Regular Contributor
timestamp: January 07, 2018, 08:56:02 am
content: This is the composite grating spectrum of Spectrum 1 and Spectrum 3.However, the colors are strongly distorted by the camera's automatic white balance.The question is still:Which gas corresponds to this spectrum?regardsPhysikfan

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 07, 2018, 06:08:18 pm
content: Is that second band actually yellow or green? If it's green it might be argon as I suggested above, if it's yellow, we'll have to keep looking.

author: james_s
author_rank: Super Contributor
timestamp: January 08, 2018, 07:22:40 am
content: There may well be more than one gas in there too.

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 08, 2018, 05:31:54 pm
content: Quote from: cleaningOut on January 08, 2018, 07:44:30 amMaybe? Here's carbon monoxide, not sure how it compares to carbon dioxide. Of course it could have decayed as someone suggested.If it was a mixture, there should be more lines, but of course the OP's crude spectrum may not be picking them up.

author: james_s
author_rank: Super Contributor
timestamp: January 08, 2018, 06:03:19 pm
content: Hm I had not realized argon had such a broad spectrum. Neon also has quite a few distinct spectral lines in the red-orange region. I've always thought gas discharges are pretty cool.

author: Cyberdragon
author_rank: Super Contributor
timestamp: January 08, 2018, 06:25:06 pm
content: Quote from: james_s on January 08, 2018, 06:03:19 pmTake spectrums with salt. Some elements seem to vary based on the setup used (probably due to measurement sensitivity, like the argon spectrum I posted before looks really dull)EDIT: The one before actually shows green lines where as this one doesn't

author: Physikfan
author_rank: Regular Contributor
timestamp: January 13, 2018, 06:22:46 pm
content: I will use such a transmission grating spectrum of a fluorescent lamp (mercury lines) to calibrate the lines of the Geissler tube,green line 546 nm.

author: Samogon
author_rank: Frequent Contributor
timestamp: January 14, 2018, 01:52:19 pm
content: Xenon has white grey-ish white color electric discharge of high voltage