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Rebuilding Paper Capacitors
This is my procedure for rebuilding paper capacitors:
1. Remove the old capacitor from the circuit. I usually do 3 or 4 at
a time, using alligator clip jumper cables to mark the two ends. I
make a sketch to note which capacitor goes where, and which end is
the ground end (though modern capacitors don't have a ground end, the
sketch allows the rebuilt capacitor to be re-installed in the exact
same way as the original).
2. Heat the capacitor with a heat gun. By heating the sides of the
old capacitor, the wax will melt and drip off. This will remove the
years of accumulated dirt. The wax holding the guts in will melt,
allowing the leads to be pulled out from each end. The remaining
material inside can be scraped out. Use the low heat on the gun, and
be careful not to burn the cardboard.
3. Wrap a new capacitor with paper to make the total diameter of the
capacitor and paper slightly smaller than the inside of the old
housing. Insert the new capacitor in the housing. If the fit is not
snug, the hot wax will drip through. Note: new capacitors are much
smaller than the original ones. In some cases two capacitors can be
put in series or parallel to get odd values or higher voltages. Both
will usually fit in the old shell.
4. Using the heat gun, melt candle wax of the same color as the old
housing. A tin can with a small spout made with pliers works great to
hold the wax. Support the capacitor with one end up, then pour the
wax in the end and allow it to dry. Turn the capacitor over and pour
wax in the other end. Another approach is to use a hot glue gun. Colored
glue sticks are available from glu-stix.
5. Re-install the capacitor in the circuit.
6. Often capacitors have been replaced with modern (postwar)
ones. In order to make the chassis look as authentic as
possible, I remove the modern capacitors. I also remove the paper
label from one of the prewar capacitors in the set and scan it into
my computer. I then use Photoshop to create new labels for the
capacitors which had been replaced with modern ones. Using
Photoshop, I change the capacity and voltage on the label to match
the values I need. Old capacitor shells salvaged from immediate
postwar sets are then rebuilt as described above. The labels are then
glued to these capacitors.
7. Not all capacitors can be rebuilt in this way. Some, like the ones
in the HMV sets, have the ends of the cardboard crimped around so
that it is impossible to open them without destroying the shell. In
this case I use a razor knife to make a cut from one end to the
other. Then, I remove the old capacitor, insert a new one, and glue
the shell back together. When it is replaced in the set I orient the
cut side down so it won't be visible.
Others, like those in the RCA sets, have the ends crimped around, but
they can be opened up without damage. I open one end, remove the old
capacitor, install a new one, and then recrimp the end. I use
superglue to reseal the end.
Here is a chassis undergoing capacitor rebuilding. The clip leads
mark where capacitors have been removed. I write down the value of
the capacitor, together with the color of the clip lead. At the top
you can see the 5 capacitors hanging from the edge of the chassis,
waiting for the superglue we used to seal the ends to dry.
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