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Hints, Tips and Solutions (Do NOT post requests for help here) If you have any useful general hints and tips for vintage technology repair and restoration, please share them here. PLEASE DO NOT POST REQUESTS FOR HELP HERE!

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Old 10th Dec 2011, 4:13 pm   #1
Ricardo
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Default Metal can capacitor - replacing internals

I am working on the restoration of a No.10 Crystal Calibrator which contains a large number of small 0.1µF, 350V metal can, stud mounted capacitors.

Initially I did not intend to replace any of these capacitors as they seemed to test OK with what I thought was reasonably low leakage. However the 1 cycle per second modulation circuit was found to be inoperative due to the leakage in several of these capacitors.

There is limited space within the case to disconnect the existing capacitors and simply fit replacements. So I set about the task of emptying the old capacitors and replacing the discarded innards with modern polypropylene capacitors.

I have previously re-stuffed wax paper capacitors in 1930s radios, but had not tackled a metal can capacitor before.

There is nothing particularly novel in the method that I used, but certain aspects might perhaps be informative to others. As such I took a sequence of photos to illustrate the process. See the attached PDF. I hope that the photos are generally fairly self-explanatory. The inner sleeve used when re-assembling the two halves of the metal can is made from a short length of plastic radiator pipe cover.

Let me know if anything is unclear from the photos and I will add some further written details.


Best regards,

Richard.
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File Type: pdf Photo guide to replacing capacitor in small metal .pdf (252.6 KB, 492 views)
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Old 10th Dec 2011, 5:06 pm   #2
M0FYA Andy
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Default Re: Metal can capacitor - replacing internals

Richard,

Very interesting!

Are the two halves finally glued together? With what -Araldite?

Andy
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Old 10th Dec 2011, 5:57 pm   #3
ms660
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Default Re: Metal can capacitor - replacing internals

Well documented Richard.

I have done a couple of capacitors of a similar construction a while back, i used the circular recess running round the outside of the can to advantage. In a lot of cases the two different diameters do in effect equal to two concentric tubes one runing within the other at an almost interference fit.

I used a fine saw blade to cut the capacitor in two (imagine the capacitor on a table with that recess facing towards the right) I made the cut at the bottom of the lefthand shoulder of the recess, all the way through until the capacitor was in two pieces (a square cut is the key to success) Then removed all the inards. With fine circular and flat files I removed any burrs from the cut then filed the inside of the shoulder of the left hand half until its inside diameter is exactly the same as the diameter of the recess part, (Push and fine file to fit, it's usually soft metal)) so that it was an interference fit.
Fitted new cap etc, new capacitor lead was cut off close to it's body and a longer thin flexible insulated wire was "quickly" soldered to the short wire stub that was left then connected to the outlet tag (wrapped round tight and soldered) Pushed the two halves of can together with just a mm or so overlap, marked overlap, pulled apart, applied a very thin application of super glue (Araldite will do if you clean up quick) pushed two halves back up to the mark, cleaned the mark off, this results in the original body still retaining its rolled recess with no or very little visible join.
I also used this technique on a large electrolytic once and achieved the same results.

Lawrence.
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Old 10th Dec 2011, 6:01 pm   #4
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Default Re: Metal can capacitor - replacing internals

I have restuffed some of these caps, but I uncrimped the cap. In some cases this damaged the black insulator bit, but it was easy to turn up a new one.
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Old 10th Dec 2011, 6:18 pm   #5
ms660
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Default Re: Metal can capacitor - replacing internals

Hello Graham what material do you use for your new end caps?

(Addition) I was thinking that if a suitable material was found with a bit of "spring" that could easily be cut/turned then once the new capacitor is in then the new end cap could be "snapped in" ie: old can not touched at all, old end cap sacrificed for access and replaced with new replica.

Lawrence.

Last edited by ms660; 10th Dec 2011 at 6:31 pm. Reason: Addition
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Old 10th Dec 2011, 6:22 pm   #6
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Default Re: Metal can capacitor - replacing internals

Some plastic sheet which I just happened to have. No idea where it came from. I have also cut material from black plastic gutter fixing brackets. You can use the material from plastic gutters if they're the square rather than the round type. Make sure the plastic is flexible and not the brittle type which shatters.
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Old 10th Dec 2011, 6:49 pm   #7
Lucien Nunes
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Default Re: Metal can capacitor - replacing internals

I have used this method, by cutting discs of black rubber out of a sheet using wad punches.The rubber can be stuck into the end of the can or if you are lucky with thickness then it will hold by itself between the groove and the return at the mouth, just as the original plug did. As it doesn't have to seal it can be a much looser-fitting and more flexible rubber than the original. By fitting an eyelet through the hole in the middle it is also retained by soldering to the emerging lead.

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Old 10th Dec 2011, 7:01 pm   #8
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Default Re: Metal can capacitor - replacing internals

When restuffing any capacitor, which has solder tags, it's always best to bring the leads of the new capacitor/s out through the end caps and solder them to the tags on the outside of the can. Never rely on a screw or rivet to maintain continuity from the inside to the outside of the can.
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Old 10th Dec 2011, 8:34 pm   #9
Ricardo
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Default Re: Metal can capacitor - replacing internals

Thanks everyone for your comments and suggestions.

Andy,

I have only completely assembled one of these capacitors so far and it has not yet been glued. The two halves seem to be held together quite rigidly by a combination of the expanding inner sleeve (radiator pipe cover) and the new capacitor. The radiator pipe cover has a nominal diameter of 15mm and has to be compressed to fit within the capacitor can which has an internal diameter of about 11.5mm.

Lawrence,

I like your suggestion of using the recess around the solder tag end of the capacitor to produce a re-assembled capacitor with a less visible join.

Graham and Lucien,

Had this capacitor been a standard axial type with leads or solder tags at both ends I would most probably have used your approach of removing and replacing the end cap(s). However I could not do this at the end of my capacitor with the 4 BA mounting stud connection. The original capacitor made connection somehow to the inside of the metal can at that end. I think there might have been a metal disc, but it was only a press fit inside the can. I didn’t think that a soldered connection to the aluminium would be very good, so I used a solder tag with a small nut and bolt to make the connection instead. I’ll probably add a shake-proof washer to improve this connection. The only alternative might be to drill a hole in the end of the can and wrap the capacitor lead around the 4BA stud instead.



Regards,

Richard
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Old 10th Dec 2011, 9:21 pm   #10
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Default Re: Metal can capacitor - replacing internals

Quote:
When restuffing any capacitor, which has solder tags, it's always best to bring the leads of the new capacitor/s out through the end caps and solder them to the tags on the outside of the can. Never rely on a screw or rivet to maintain continuity from the inside to the outside of the can.
I always re-stuff smoothers on most sets if needed, as it would spoil the appearance above the chassis usually reuse the base with tags, drill small holes next to the tags bring the leads through solder to the tags.

As they say on, here's one made earlier.....

Mark
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