Recycling of vintage paper capacitors.

When restoring a really old, vintage radio one of the things to do is to replace all leaky paper
capacitors. If you are a real afficionado you want a direct original replacement, which usually
is quite unobtainable. And if you against all odds should find them, they are most likely to be
 just as leaky as the ones you want to replace. So what do you do? Put in a "poly--something-
capacitor"? Disgusting!! However, there might be another way out.
Consider the question: Why does a paper capacitor leak? And also: Why does a paper capacitor
sometimes behave as a battery of a few tenths of a volt. The explanation close at hand is that
it has got something to do with electrolytic action and that the electrolyte is moisture (water)
that through the years has penetrated the exterior seal and has entered the paper insulating layers. So, let`s set the process in reverse to solve our problem. This is most readily done by
heatig the capacitor in molten paraffin wax at a temperature well above 100 degrees centigrade.
 The initial strong boiling will after some time subside and eventually stop. Now, set the wax-pot
aside for coolig with the capacitors in the wax until just before the wax solidifies. Then, take the capacitors out and let them cool to room temperature. Now, make a leakage test with a 100
megOhm ohm-meter. Also, make a test at a voltage at least as high as the working voltage
stamped on the capacitor. Criterion for renewed service: no appearent leakage. The specimen
fit for service will then have their ends sealed with wax - use a clean soldering iron- and may be
given a little cosmetic touch. Then solder them back into the circuit and: Power UP!
Some capacitors will not pass this test. One reason for this can be that the insulating paper
has suffered unrepairable damage by corrotion of the metal film in the stack. Walter Knutsen.

To thank the Author because you find the post helpful or well done.

To thank the Author because you find the post helpful or well done.

I agree with Omer! I think it is rather better to refurbish an old capacitor by taking out the old stuff and putting in a modern one than to rely on old leaky "bombs".  As Omer said, the question is how long is it lasting? For me it is more important to have a reliable radio, rather more than an electrical risk!

 

Kind regards

Olaf

 

To thank the Author because you find the post helpful or well done.

It would be great if someone could scan the  cover/label portion of paper caps, place it in a specific area on this site, so that they can be downloaded and printed on paper,and placed over new yellow axial mylar capacitors.  Thus , retaining the original look of the radio's innards.

To thank the Author because you find the post helpful or well done.

As scanning of round capacitors is a little bit difficult - and the size will not fit in most cases with the size of the new smaller c's, I prefer to redesign the old labels. I use Photoshop and try to find similar fonts. Then I print them out on self adhesive labels. Top and bottom get a black painting, CD-marker like Edding 8400 do a great job.

I just worked on a German "Saba" "Freiburg 100" radio and changed 27 paper-capacitors. The labels will fit on those yellow caps, you can get at justradios.com . May be, they are usefully for someone.
Easter greetings from Germany
Martin Renz


to be printed with 300 dpi

To thank the Author because you find the post helpful or well done.

To thank the Author because you find the post helpful or well done.

Just another humble idea: when the newer capacitor is much smaller that the older one (which happens most of the times) but not enough to be hidden inside, I PASTE the old one (not connected, of course) over the new one with a drop of silicone, so that the newer one is hidden and the aesthetics are preserved. Same thing with resistors.

In most cases, however, the paper label of the old capacitor peels off very easily and can be used as suggested by Martin.

To thank the Author because you find the post helpful or well done.

If have scanned labels for BB (French?) capacitors but the uploader rejects files larger than 200kB.

So if anyone needs these, send me an email and I'll gladly send them to You.

Dejan (dizdard@yahoo.com)

To thank the Author because you find the post helpful or well done.

Hello,

For my Philco 38-12, i "make" some capacitors.

Only one is original.

See this pictures

Best regards

Carlos

To thank the Author because you find the post helpful or well done.