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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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Last time, we restuffed a box type capacitor with new electrolytic caps.
That was easy. Now, we tackle the popular wax/paper capacitor. Old radios
are just full of these wax and paper creations. |
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All antique radio restoration
experts agree that every wax/paper capacitor should be changed
before the radio is used. When your antique radio was made, this was
the extent of capacitor technology and was good for its time. Today,
these are time bombs. As the wax and paper age, they disintegrate
inside, and the foil rolled inside the paper will begin to age as
well. Eventually, the capacitor will fail short when voltage is
applied, and the resulting short can damage other components in the
radio like coils and (God forbid) the precious power transformer.
Even wax/paper capacitors not yet shorted will almost always test
very leaky, which means they allow current to flow through them like
a resistor. For audio circuits, this can cause distorted or fuzzy
audio. In some bypass cases, it can mean improper grid voltages on
tubes. That will lead to early tube failure and damage.
Since the wax/paper cap is the most abundant cap in an old radio, it
makes sense to tackle this next. The trick to keeping the capacitor
shell together is to avoid being rough with it. Remember that this
is just a paper tube. You cannot use hammers on them. If possible,
it is very advantageous to save the original labels too. Since the
labels are printed right on the paper rolls, you must be careful
with application of heat or chemicals. |
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| Removing the wax and paper cap
from the outer paper shell is time consuming, so do not be in a
rush. Sometimes you get lucky and the fit is not too tight. That was
not the case with this unit pictured here. I suggest using a heat
gun to melt away the wax on the ends and gently push the guts of the
cap out the hot end. The whole cap usually does not need to be
heated since there is seldom any glue or wax inside the paper roll
itself, just the outsides. Try to avoid pulling the leads to remove
the guts, this will usually just result in the lead pulling away,
and you will cuss. |
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Once the guts are out of the paper roll, use tools
to remove any residue from inside the tube. Now, install a new
metal/film axial capacitor (use the same value, obviously). I use
either silicone or hot melt glue to seal the new cap inside the
paper tube. I prefer to leave the clear silicone or hot melt glue
visible at the ends of my restuffed capacitors so I know they are
restuffed. However, if this is objectionable to you, then I have
found that 3M's 5200 Mahogany colored sealant is nearly an exact
match for the reddish/brown goo they used to seal the ends
originally. If you take this option, I highly suggest you also make
a note somewhere under the chassis so another restorer does not go
through and rip out all your handiwork! |
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| Back to the job.. As the adhesive
is firming up, be sure the capacitor leads are kept centered in the
tube. Nothing will ruin the authenticity more than having leads all
crooked. Retest the capacitor to make sure it is still proper value
and not shorted or damaged, then reinstall in the radio. Enjoy your
'original' old radio! |
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Next time, we will restuff
multi-value wax/paper capacitors popular in the 1930's. |
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