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‘Restuffing’ a capacitor is the art of repairing old
capacitors by replacing the electronic component inside with modern
capacitors and therefore retaining the original outward appearance while
making the part again truly functional. It is a well debated fact that
almost nobody will ever look under the chassis of your old radio to see if
the capacitors look original! However for some restorers, the satisfaction
of retaining the complete originality of the radio while also making it work
well and safe to use is most satisfying. |
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In the 1930's and even right up to WW2, it
was common to find capacitors in radios that were really two capacitors in
one. In this example, you see three connections. One lead comes out each
end, and a metal band around the shell of the capacitor is the third
connection. Most of these types of capacitors use the band as the common and
each end lead is a separate small value capacitor. Occasionally, an end lead
may be the common, you have to examine the description on the shell to be
sure (or consult your schematic if available). |
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Restuffing this type of capacitor is essentially
the same procedure as the normal wax/paper capacitor we restuffed in
the last installment. The only difference is the wiring inside that
must be done correctly. Begin by using your heat gun to carefully
heat up the wax on the ends and remove the small cardboard end caps.
Put these aside for later. Choose which end you will be shoving the
innards out, and work the innards that direction by applying
pressure with a nut driver. Do not pull on the leads because you
will only pull them away from the foil inside. The paper end will
unroll and the guts should come out easily.
After the guts have been removed, clean the inside of the cardboard
tube and be sure to remove any wax from the small braided lead that
connects to the metal ring. Be careful to not damage the ring lead,
it is a little fragile. |
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Choose some new metalized Mylar capacitors of the
appropriate value and wire them accordingly. In this example, the
outside metal ring is common, so as you can see in the photo, the
ends of the caps simply solder together and the braided ring lead
also solders to this common point. Be extra careful that you do not
pull too hard on this lead. If you do, it will be a real difficult
task to reattach it to the metal ring! You will cuss.
Once wiring is complete, it is time to put the new guts inside the
cardboard shell. BE CAREFUL that the common lead does not come into
contact with the outer capacitor leads! Either use some heat shrink,
or use hot melt glue to insulate the common lead from the outer
leads. Use hot melt glue or silicone sealant to fasten the new caps
inside the cardboard tube, keeping an eye on alignment. You should
keep the caps centered in the tube lengthwise in addition to keeping
the leads centered in relation to the outside diameter. |
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| Once the glue has
set, re roll the open end that was used to remove the old guts. I
use low heat and a screwdriver to slowly go around the edge evenly
and roll it back inward. Keep the heat on so that the wax
impregnated paper stays pliable. If it cools too much, the paper
will whiten (as it did here a little). |
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After your glue sets up, attach the two small
cardboard tubes to each end for a finished look. Use hot glue or
silicone to fill the holes completely. If you want your caps to look
completely original, use 3M 5200 mahogany colored adhesive/sealant
for this task. If you do, it will be extremely difficult to tell the
cap has been restuffed. For this reason, I use silicone to seal the
ends of my restuffed caps so I can TELL they have been restuffed!
You do have to look close to be able to tell though.
Once the glue has set, retest both sections of the
cap with your capacitance meter to be sure it is correct. Sometimes,
excessive heat will damage the newer caps, so it is always a good
idea to double check them before installing in your radio. Use the
heat gun or some acetone to clean the shell when finished if you
like. Reinstall in the radio and it will look like it always
did, only now the radio will be safe and work! You cannot tell this
cap is new inside (see pic.), but it sure sounds like it. |
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Next time, we will tackle
restuffing aluminum can electrolytic filter capacitors. |
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