Rebuilding Those Old Capacitors:
We all know that most 50+ year old paper and electrolytic capacitors have to be replaced in these old radios.
So now the age old question? do you just solder in replacement capacitors and scrap the old paper tubes and
metal cans? or do you take the time to restore and refill that old can or tube? I prefer the latter, It is so cool
to see an old radio chassis working with what looks like its original paper and can capacitors.
WARNING:
When rebuilding any old capacitor (can or tube) you should protect yourself from its contents!
This means latex gloves, and a 3M filter mask. dissasembly should be performed outdoors if possible.
The contents of these old capacitors is most likely TOXIC !!. Not to mention the fact it is gross. Below is a
picture of the primary capacitor bank (from the 1928 Bremer Tully Power Supply) removed from its
can. You will now need a tetanus shot from just viewing it!!
I very carefully dissasembled the whole capacitor bank to help ascertain the values of the individual capacitors
inside. The picture below shows some of the individual paper and foil capacitors that were sandwiched together
in the block and thier new modern replacements resting on top of them. Thankfully the modern replacements
are much smaller that the originals which makes replacing them a lot easier. The original capacitors were all
dated Nov. 1927 and some of them are still in working order.
With everything dissasembled the capacitor can was stripped primed and repainted black. The inside of the
aluminum can was cleaned and degreased so adhesive would work with it. I used 3 small 1/8" thick plexiglass
plates to mount the new capacitors on. The Capacitors are mounted to the plexi by means of high temp glue.
Since these capacitors far exceed the original voltage rating called for, overheating is not a problem. The other
big plus is the modern metalilized polyester capacitors have no polarity issues, they work either way. There
are a lot of capacitors in this one can (7), all are mutual ground except for one. This paticular power supply
uses large 1.0uf 630V and 2.0uf 630V paper capacitors for DC filtering instead of the electrolytic type.
Below is the picture of the new capacitor block assembly. Fully tested and ready to go back in the can.
All back in the can and ready to go another 84 years, All the wiring is cloth reproduction wire in
the correct color. No special diagram needed, it matches the schematic. I realize no one may see
this work again for 100 years or even ever!!, but I know its there and it will all work from the
original container.
Below is the finished product with the top back on, 84 years old and factory fresh again..
This unit has been remounted and tested in the power supply and is functioning just fine.
Ok, now on to the paper tube capacitor rebuild. The picture below is of one of the capacitor banks in
the 1934 Philco model 32. This is the "before picture" taken before the fun begins. This chassis was
still 90% factory correct and appears to have been serviced at least once in its life.
Now the fun begins. Before removing the caps make sure you carefully document thier location and
polarity if it is an electrolytic capacitor. Once cut from the circuit make a small foil tray which will
hold the caps at about a 45 degree angle. Place the caps into a PREHEATED toaster oven set on
bake setting (will run both upper and lower elements) at 250 degrees F for about 5 minutes, Keep
a very close eye on them, You'll see a large puddle of wax that will form at the low end of the capacitor.
Using a shop towel to hold the body of the capacitor ( it will be HOT! ), you can pull out the old contents
of the tube by pulling on its wire with a set on needle nose pliers. Lightly wipe down the outside of the
tube with a soft cloth, excessive pressure could remove any printing.
Note: This process smells and smells bad! I highly reccomend you perform this outdoors and please
avoid breathing the fumes.......
Below is a picture of some Philco tube capacitors fresh from the toaster oven
With thier insides pulled from the tubes
With the cardboard tubes empty and clean you can insert the replacement capacitor into the tube. The new
capacitors will be a bit smaller in diameter so I wrap them in small amounts of electrical tape to achieve a
slightly snug (centered) fit. Place the capacitors in a vertical position so each end can be refilled with wax.
I used pure carnuba wax to reseal these capacitors, it has a high melting temp and is easy to work with.
Take an aluminum food can and attach a small metal handle to the top of the can. Using pliers make a
small pouring dimple at 45 dregrees to the handle. Using the toaster oven again heat the carnuba wax to
250 degrees F until liquid. Only fill the end of the capacitor about half way with the wax and wait for it
to setup. After 30 minutes you can fill it in the rest of the way (this avoids sink holes) then wait another
30 minutes before turning it over to do the other end. After 24 Hours they are ready to go back into service.
Below is a picture of a capacitor about to be filled with carnuba wax. Note the use of easy release tape
in case the wax overflows.
Below is a picture of some finished capacitors ready to be reinstalled
Below is a picture of the fully restored lower chassis of the 1934 Philco Model 32.
All the paper tube and electrolytic capacitors have been rebuilt and it looks very
original and unmolested. Sure, you can just cut out the old and solder in the new,
but with a little care and a bit of time it can appear nothing happened at all.....
Thanx for Visiting the capacitor rebuilding page. If you have any questions/comments just drop me a line at