Rebuilding Electrolytic Capacitors

I have rebuilt or fixed a lot of vintage radios and televisions over the years. A lot of the problems that you will find with the old electronics are that the power supplies have failed because of the old electrolytic capacitors going bad. There are companies out there that will sell new ones for the rebuilder but they are getting pretty expensive. When I started in electronics, electrolytic capacitors were usually only in the five to six dollar range. Now that I look on the Internet they sell for a close match of the original for thirty-five to forty dollars. This makes the restoration a lot more expensive plus with the other parts that are needed. This article will discuss the procedures that I use to rebuild those capacitors.

Here in the last month I have updated my web page with my last project, a Dumont Television from 1955. What I will show here is that you can use this procedure with any of your vintage equipment. I still have some older radio's to put back into operating order this winter and I will use the same procedure as shown here.

These instructions will be used specifically for the metal can electrolytic like the one below

The first step is to document all of the connectors on the old capacitor. You should make drawings of the connectors and trace out all of the wires with the schematic so that you can tell where the connections should go. I tend to like to take pictures and label the wires. This capacitor also has a resister connected between terminals. Make sure you have documented all of them.

The next step is to unsolder all of the connections. I use the old Weller Guns mine is rated at 140 to 240 watts. I also use a desoldering bulb or solder sucker. Since there is so much metal and mass at the connectors you need to have a lot of heat to melt the solder and remove the wires and components. I do have an old Heathkit soldering iron that was built by GE. I use it to assemble project boxes using old printed circuit boards. It also would provide the heat to clean up the connections.

When you get the connectors clean and the wires removed you will need to straighten all of the tabs that hold the capacitor in the chassis that you are working on. It will be a tight fit you can work the capacitor out of its slots.

Here is what it should look like:

Here is the capacitor out of the chassis. What is nice about this rebuild is that I am using the same case that has the Dumont part numbers. Well lets get on with the rebuild. As you can see, I keep scraps of board in my shop just to be able to cut and gouge on.

Let us start out with some safety. I have in the past impaled my fingers and hands. Now days I use leather gloves and try to watch in which direction I am using my sharp tools (always away from the body).

I started out trying to use a knife to pry the bottom off the case. I realized that the blade might break and you should not pry with a knife. So I found a very small blade on a screw driver. It seems to take the prying pressure a lot easier.

Here is a picture of the prying process:

Next pry up the sides of the capacitor until you are able to remove the complete ring that attaches the capacitor to the chassis as shown:

In this step we will use a heat gun to heat the metal-can so that the black tar will melt to remove the inside material. Use leather gloves so that you do not burn your hands. I use a small scribe to insert in the holes of the connectors to remove the insides. I have done two of these now and the insides did come out pretty easily.

Here is a picture of the insides removed:

You will have to cut the lugs off of the capacitor insides so that you can reuse the bottom connectors of the capacitor. Here is a picture of the bottom of the capacitor remove ready for the rebuild the process:

After you clean up the inside of the metal can with a flat blade screw driver we can start the rebuild process. Cleaning out all of the old black tar was pretty easy. I read some articles that the guy’s would use paint thinner to get out all of the tar. I did not do that I just cleaned out the bulk of the tar. It did not seem to hurt anything to leave some of it in there. I did wash out all of the old electrolytic material using soap and water. I am not sure it would hurt anything to leave some of it there but I did not want to take a chance over time

The capacitor that I was rebuilding was a four section capacitor. When I talk about sections it is like you have four individual different capacitors built in one unit. The capacitor's value that I was replacing was two 40 mf sections one 20 mf section and a 10 mf section. Each section voltage rating was 300 volts. I ordered individual capacitors from Mouser Electronics. The values that I order were 47 mf and 10 mf at 350 volts. The 47 mf would replace the 40 mf sections. The 10 mf capacitors would replace the 20 mf at 350 volts. Remember capacitors in parallel will add their values. So I will parallel two 10 mf to replace the 20 mf capacitor. The last I will use a 10 mf capacitor to replace the 10 mf section.

Here is what the capacitors look like before assemble in the can: Note: Do not look to close a the values I mixed some of my photos with different capacitor rebuilds:

The next step is to drill a small hole next to each terminal connector so that you can wire each individual capacitor to each terminal.

Here is a picture if you look close at the bottom to see the capacitors tied and soldered to the terminals:

Note: the wire on bottom left coming out of the bakelite bottom is the ground and will be soldered to the metal ring that we removed prying off of the bottom of the capacitor.

Here is what the build looks like before I put the metal can back on it:

I did not take a picture of the completed capacitor but it really turned out good. I slipped the new insides back in the metal can then the metal ring with the twist tabs. I then took a small hammer and bent back down the edges of the capacitor that I had pried up. The common wire or ground for all of the capacitors must be soldered to the metal ring. This completes the rebuild process. It looks like no one ever replace the old capacitor and I was able to bring it all back to life.

Thanks for looking, if you have any questions please e-mail