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Author Topic: Repairing old bulbs  (Read 9257 times)

Offline James

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Repairing old bulbs
« on: July 11, 2001, 08:17:00 pm »
How often have you found some special old bulb, only to find that its tip has been knocked off rendering it pretty much useless?  A few weeks ago on Ebay I noticed a couple of auctions for old street-series carbon lamps, one of which had suffered such damage and was attracting no interest at all, despite its beautiful internal construction with blue-glass insulators on the stem.

The price was ridiculously low for a lamp of this type so I decided to have a go at repairing it myself and thought other forum members might be interested to see the results!  I'd also be interested to hear anyone's comments on the ethics of repairing old bulbs, even if the repair can be carried out in precisely the same fashion as the bulb would have been originally made.

Anyway, shown below are some pics I took during the process, which proves that this kind of thing certainly is feasible.  Let me know what you think, and if anyone should have some rare old bulb that has a missing tip, it might well be worth taking it to a skilled local glassblower.

   

BTW I didn't get the vacuum quite good enough in this particular one, hence the blue glow when coil testing is a fair bit stronger than I would like.  The lamp will still work fine but next time I'll know they need a more thorough attempt to outgas the glass.

James.


Okay well photopoint seems to be playing up a bit at the moment, but if you point your browser to http://albums.photopoint.com/j/View?u=1148573&a=8437387&p=51671324&Sequence=0&res=high  the pics seem to come up fine.

[This message has been edited by James (edited July 11, 2001).]

[This message has been edited by James (edited July 11, 2001).]

Offline Bob Masters

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Repairing old bulbs
« Reply #1 on: July 12, 2001, 12:34:00 pm »
James,

Ha Ha Ha.......this is drivng me nuts !
I wanna see this groundbreaking experiment.
This could be the beginning of something BIG.
Imagine someone deliberately removing the tip to gain acess to a broken filament, then repairing the tip like you describe........
just imagine the implications........

WOWOWOWOWOWOWOW !
-Bob-

Offline Bob Masters

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Repairing old bulbs
« Reply #2 on: July 12, 2001, 12:54:00 pm »
Food for thought..........

As for repairing old bulbs ?

Does restoring a vintage autombile diminish it's value ?

Is a faithfully restored vintage electric fan worth more, or less, than the same fan badly in need of restoration ?

Are we allowed to re-wind vintage electric motors ?

This is truly ground-breaking territory.

-Bob-

Offline ALM

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Repairing old bulbs
« Reply #3 on: July 12, 2001, 01:28:00 pm »
Let's see here...  I have a non-working or broken bulb that is likely worthless to me...

I can - DO NOTHING - and it remains useless and worthless.

OR...

I can - FIX IT - and it works, thus, making it valuable/useful for the collection or for somebody else.

Fix it.  What "implications" should there be?  Let's be realistic, is somebody gonna hunker down and do this to several dozen, several hundred, or several thousand bulbs in an effort to "rip-off" collectors via resale with no disclosure?

I'm imagining that this is a painstakingly tedious process... and not one someone would use to negatively impact the value, the history, the collectibility of bulbs.

I have to go with Bob on this one... I can't imagine that it does anything except add value to the piece.

Offline Chris W. Millinship

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Repairing old bulbs
« Reply #4 on: July 22, 2001, 10:47:00 am »
Photopoint can be a pain in the toliet-muscle sometimes can`t it? James`s picture up there has never appeared for me- and I expect a good few others of you havn`t been able to see it either. Well I offered to host it for James so we can all finally see it- my new image host seems stable enough so Bob, you can stop drooling into your keyboard now   ...






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Offline Bob Masters

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Repairing old bulbs
« Reply #5 on: July 22, 2001, 05:21:00 pm »
I am thoroughly impressed with that series of photographs ! What a magnificent array of equipment to do the repairs with. I couldn't tell that the finished lamp had ever been repaired.
I believe a lamp repaired to the level that you show would not require any mention of repair because the repair shows no signs whatsoever. I would call it a fine restoration of the highest level.

Excellent ! Magnificent !
And now...........how many repairs like that can you do per hour ? Ha Ha Ha Ha...........
.........and we can all send our "Duds" to what address for a free repair ? Ha Ha Ha.....

Offline James

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Repairing old bulbs
« Reply #6 on: July 22, 2001, 10:20:00 pm »
Thanks for posting the pictures Chris, and for your comments as well Bob!  Actually the repair didn't take all that much time.  I left it for an hour pumping down on the exhaust bench, but the actual time involved in me working on it and doing the glassblowing was much less.  I am open to offers should anyone have any other bulbs that could benefit from such a repair!

As you pointed out, it should certainly be feasible to re-attach broken carbon filaments as well and I plan to try that out next, will keep you posted on how it goes!

James.

Offline Chris W. Millinship

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Repairing old bulbs
« Reply #7 on: July 23, 2001, 06:00:00 am »
As you pointed out, it should certainly be feasible to re-attach broken carbon filaments as well and I plan to try that out next, will keep you posted on how it goes!



You wouldn`t like to try that on my big old red one some time would you? You know the one- it got damaged in transit last summer? I had finally just written it off as bad luck and decided to leave it as-is, but seeing your pictures has got my confidence back up that you`d be able to pull off an expert filament repair and re-exhaust it too, leaving one working lamp again. OK it has a red glass tip now, and as you told me before, you`ve only got clear tubes but it`s a small price to pay, to see it glow for the first time. I can always paint it red after with some clear stained glass paint, wherever that stuff is sold.

What do you reckon then? Fancy giving it a try? Let me know!

   



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Offline James

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Repairing old bulbs
« Reply #8 on: July 23, 2001, 09:47:00 am »
Hi Chris,

Yeah sure I don't mind trying it, but must point put that there is always a very small risk that I might make it worse.  Its never happened to me before, but if there are very high levels of stress in the glass, then it could crack as soon as I put the flames on it.  If that happens, you'd get a ring-shaped crack about 1" dia. around the tip and I would not be able to repair that.

Re. the red tip, depending on how big the tip is I could probably use the original glass.  If I cut off the old tip and it's large enough to hold in the flame, I can re-draw it to a tube again and re-attach that, with a clear extension piece on the end that would all disappear after re-tipping.

Anyway let me know what you want to do.  It would certainly be an interesting thing to try if you are prepared to take the very slim chance that it could crack.

James.


Offline Chris W. Millinship

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Repairing old bulbs
« Reply #9 on: July 23, 2001, 10:54:00 am »
OK, I`ve thought it over and I`m willing to give it a go- and I`ll not hold you responsible if it fails   . I`ve waited so long to see this big old one glow and was so dissapointed when it arrived broken that I felt quite down, all the rest of the day! Well I`m like that   .

Here`s a few pics of it, pre-surgery...









Let`s give it a try, if only to see if it`s feasible or not. Regrettably the other 3 dud carbons I have here all have breaks mid-filament so am I right in thinking there is no hope for those? If not let me know cos one of them is a Sterling with that unique helical shape. Lucky in a way that the big red one broke at an anchor point where in theory it can be re-attached with a dollop of carbon paste.





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Offline Carl U

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Repairing old bulbs
« Reply #10 on: July 25, 2001, 06:24:00 pm »
Hello James and all,
I read the posts regarding the bulb repair techniques with much interest.

I have a collection of mostly vacuum tubes, with some light bulbs. I have a number of vacuum tubes with either broken exhaust tips or worse. Generally, with the availability of tubes, I suppose it wouldn't be worth the trouble to repair most tubes. But some deserve a second chance. These tubes might have a snapped exhaust tip, or open filament.

(I hope this is not off-topic - bulb repair).

James, do you feel these bulb repair techniques, or internal surgery, could be applied to vacuum tube envelopes?

Carl

Offline James

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Repairing old bulbs
« Reply #11 on: July 25, 2001, 09:12:00 pm »
Hi Carl thanks for your comments.  To a certain extent, yes the same repairs can be carried out on vacuum tubes / valves.  But many of the more modern types could not be restored to their original quality.

In an incandescent lamp, it is necessary to pull a vacuum of about 0.01mm of mercury before it will function reasonably well.  (a mercury barometer column reads 760mm at atmospheric pressure, and falls to 0mm at perfect vacuum - so 0.01mm is still pretty good!)  However modern vacuum tubes require a vacuum somewhat better than this - really 0.00001 mmHg is desirable.  Modern vacuum tubes employ getters consisting of a barium, magesium, batalum, cetalum or one of a whole range of different metallic mirrors flashed onto the glass.  This chemically reactive film pulls the vacuum down better than what most vacuum pumps can easily attain, and holds it there during life.  Without cracking the whole tube open and inserting a new getter ring, it would not be possible to restore them properly.  They might still work, but if they did they'd show the symptoms of poor emission.

Furthermore, most tubes employ a filament activated with the oxides and tungstates of barium, strontium and calcium - this helps electron emission.  As soon as this activated filament is exposed to air, the coating is poisoned and becomes useless.  It would be virtually impossible to apply a fresh coating and reactivate it.

However despite all that, the repair can of course be done with rough vacuum for cosmetic purposes.  And if you have a really old valve which pre-dates getters and emitter materials then of course there is no problem!  When I used to work for GE someone there brought in some of his very early Audion tubes and we managed to repair those for him quite successfully.  Mercury vapour tubes are also easy since they don't require the high vacuum and its simple to dose in a new drop of mercury at the exhasting stage.

Hope this helps, just let me know if anything is not clear.

Offline Carl U

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Repairing old bulbs
« Reply #12 on: July 26, 2001, 07:50:00 pm »
Thanks James,
I now understand the challenges better.

About working with coated/activated filaments - how are these filaments originally inserted into the tube while maintaining the integrity of the coating (generally)? Is the filament coated in some inert environment, and inserted in the tube while still inert, preventing corruption of the coating?

One application that comes to mind is some old tubes (not audion-old) that are becoming scarce and are of some value, such as audio power triodes such as the type 50/UX-350 triode. This tube is of roughly late 1920s vintage. Would you expect filament and getter materials in this era to be advanced enough to prevent a successful repair of a dud?

Carl

Offline James

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Repairing old bulbs
« Reply #13 on: July 27, 2001, 08:37:00 am »
Hi Carl,

Coils are dipped in a mixture of barium, strontium and calcium carbonates suspended in an organic solvent, and an electric current applied across the tank draws a precise amount of material into the coil by a process called electrophoresis.  The coated coils are then made up into the final assembly, and sealed into a glass envelope.

While on the exhuasting machine, the filament is heated and the carbonates decompose to the oxides, evolving carbon dioxide gas.  There is then a further reaction between this gas and the hot filament that converts some of the oxide into tungstates.  In this way, they are entirely activated while under vacuum.  It then only remains to seal the tube off, and fire the getter.

I cannot re-coat a filament with this carbonate mixture while it is in place.  A new coil would have to be made, coated and then inserted into the vacuum tube assembly, and sealed into a fresh glass bulb.  You can see if filaments are coated with emitter or not, because it appears as a white coating often visible at the ends of the filament.

Getters appear as a kind of metallic mirror that has been flashed onto part of the inside envelope of the tube.

Offline Chris W. Millinship

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Repairing old bulbs
« Reply #14 on: July 30, 2001, 08:18:00 pm »
More image hosting troubles afoot! It seems NTL nuked the contents of my web space for no reason whatsoever so all my new seemingly-indestructable pics have gone. Sorry about this, it`s at least as maddening to me as it is to those who want to see the pictures. I`ll re-upload the ones on this page in just a moment but if there`s any of my old ones anyone wants to see, please say- either post a message or electriclights@ntlworld.com and I`ll mend them. I`ve posted a fair few pics here in the past, it will take qute a long time to find them all and fix them and time isn`t something I have in large amounts that often.





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