How does one "reform" electrolytic caps? I have seen mention of it but really no explaination of the process or theory. thx...

Mel

I think that Edd or someone else on here has details on the subject. You can also research it on one of the internet search engines.

I do believe that the dielectric (insulator) is a film that forms between one of the aluminum electrodes and the electrolytic fluid (which forms the other electrode...it conducts electricity, and comes in contact with another foil electrode or the aluminum can of the unit). When voltage is applied in the correct way to the capacitor, the insulative layer is formed on one of the foil pieces. As a capacitor ages, without use, the layer might break down. When you re-form an electrolytic, you build up that layer again so that the electrolytic isn't leaky.

I have re-formed electrolytics successfully at least one time. I have a whole bunch of leaky ones that I saved from my 1947 DeWald BT-100 television (RCA 630TS chassis), but I have yet to attempt to reform those units. However, I did try it with the electrolytics from my Zenith 5-G-500. I connected all of them together (except for the 25 volt unit), and connected them to a 117Z6 that I wired on a piece of wood. I fed the electrolytics through a 2000 ohm resistor for safety, and I let them sit for about 30 minutes with the power on. Then, after removing power, I discharged them very slowly with a 10K resistor. I re-installed them, and from that day on the radio has been hum-free. It used to hum slightly, but now it is perfectly quiet.

When electrolytics are in a severe state of breakdown, caution must be exercized when re-forming them. They can get quite hot, and might explode. If you re-form electrolytics, make sure that they aren't getting hot, and you might want to wear goggles. You should re-form with the maximum rated voltage so that the di-electric layer is formed to that voltage. Bring current up slowly with a rheostat, and reduce if the capacitor starts getting hot. Only increase current if the capacitor is cool or barely warm to the touch. Once you are able to apply full current, leave the unit sit for at least 20 minutes at the full current setting. You might want to monitor current with a current meter.

Actually I re-formed another electrolytic recently, when I needed a 10 MFD 450 WVDC electrolytic. I was building a power supply for my Majestic 180, and ran out of new caps. A friend of mine sent me a whole box of old caps that he pulled out of radios. I took one of the 10 MFD 450WVDC units and checked it for leakage. It had a bit...I can't remember how much, but it was perhaps 40 or 50 mA. I let it run for a long time until it had almost no leakage. The unit is now in the radio, and has been operated for 5 or 6 hours at a time with no trouble. It doesn't even get warm, and, as far as I can tell, has full capacity. I don't have a capacitor meter, though I've heard that measuring electrolytics is difficult.

Thomas

:How does one "reform" electrolytic caps? I have seen mention of it but really no explaination of the process or theory. thx...
:
:Mel

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Don't even bother, its a waste of time. Electrolytics are cheap, just replace them. You can reform, some will reform and check out good but there is no guarantee they will last. When they go they may explode causing damage to your radio. They may also destroy your transformer and catch the radio on fire.

Is it worth the risk? The choice is yours.

Dave

Dave,

I have always replaced them - but occasionally read of reforming and was just curious as to the process. I doubt a 60 year old cap will stand up as well as a modern replacement and, like most collectors, I don't operate any particular radio long enough to insure a reformed cap doesn't become 'deliquent' again. I have also heard that the paper used in older caps was acid processed and prone to breakdown.

Dave/Mel,
Good info about the reliability issue. A few months ago I purchased a multi section that noted it had been reformed on a test rig specifically for that purpose. It was a 4 section, but only needed 3 for the ckt, and the can was an exact duplicate of the original. Tested before install, found 1 needed section bad. Re-tested the orig (correctly this time), and found it OK, so wasted $$ on an unreliable, reformed cap. Nuff said.

marv

:Dave,
:
:I have always replaced them - but occasionally read of reforming and was just curious as to the process. I doubt a 60 year old cap will stand up as well as a modern replacement and, like most collectors, I don't operate any particular radio long enough to insure a reformed cap doesn't become 'deliquent' again. I have also heard that the paper used in older caps was acid processed and prone to breakdown.

I don't know why any collector who truly enjoys his radios wouldn't operate them for long periods of time. I enjoy mine thoroughly. I know of others who do as well. Why fix a radio if it is only going to sit on the shelf? It is better left original and broken if that is the case. New components ruin the radio asthetically, and serve no purpose if the radio isn't going to get used.

If I use a radio heavily, and it has expensive and rare tubes inside, sometimes I will change the tubes out for cheaper substitutes, and save the expensive ones for show, though tubes do well with a little use now and then.

Thomas

Not trying to be boastful, but my collection is such (and my free time so little) that it would be virtually impossible to listen to them all for extended periods. Personally, I can listen to but one radio at a time and a good portion of my pleasure comes from fixing something once useless from an era I much admire. In addition, the BC band has become quite a quagmire of talk, sports and Spanish - I can tolerate only small doses at one time. Although I appreciate your passion for the auditory element, I believe you likely are in a minority of collectors.

Mel,
I agree 100%. I keep my hands and mind busy, even though retired. As a matter fact, I think Silence is Golden. So much noise pollution from neighbors, sirens, blowers, mowers and the rolling hard rock/heavy metal music studios fulfills all my needs. Children playing laughing, screaming, yelling and having fun on the other hand is music to my ears, as is the purr of my small V8 truck engine. My truck radio is rarely on, except in awaiting an important news update.

marv

:Not trying to be boastful, but my collection is such (and my free time so little) that it would be virtually impossible to listen to them all for extended periods. Personally, I can listen to but one radio at a time and a good portion of my pleasure comes from fixing something once useless from an era I much admire. In addition, the BC band has become quite a quagmire of talk, sports and Spanish - I can tolerate only small doses at one time. Although I appreciate your passion for the auditory element, I believe you likely are in a minority of collectors.

I have to admit that I rarely listen to the AM dial anymore. It is a tragedy. I hardly ever use my 8 tube car radio anymore, even though it is such a fine performer. I truly do enjoy the silence in my car, especially since there is no melodic and enjoyable music to listen to on the AM dial (except on occasion, when I can get 740 Toronto, and that music is sketchy).

However, until very recently, I'd feed classical music and good jazz from the FM dial into my radios via transmitter or wire to the amplifier. I still feed them with CDs, and now I found a good classical station in South Carolina (or was it North? I forgot.) that has on-line transmissions (not the best fidelity, but it won't be noticed over my radios). When there IS good music to listen to, I run my radios a lot. I don't just turn them on to listen to whatever noise there is on the dial. My Silvertone phonograph usually gets a lot of use, too. I have a huge collection of 78s, though strangely enough I have heard all of them too many times. It is too bad that 78s aren't as convenient as MP3s or CDs, or else I'd have more than 1000. If I had more than 1000 78s, though, I'd fall through the floor.

At any rate, if you do have a ton of radios, and don't have time to put a lot of listening into each one of them, then you surely will not be able to test re-formed electrolytics. Also, for a huge collection, it isn't worth the time. It is an interesting experience, though, and I have been successful about half of the time with the process. I say that if you're curious about the idea, you should at least give it a shot several times. Don't necessarily make a routine out of it unless you have so much time to kill (I used to, but I moved out, and I go to school, and I work, so I don't really have much time for anything except listening to the radios I own that already do work....there are others that are patiently waiting for the day that I may have a lot of spare time on my hands).

Thomas,
After receiving the faulty reformed lytic and reading the enclosed brochure, I tried reforming again per text, but wo/success. Printed a couple articles on the subject from the web, and tried again wo/success. In my frustration now, with 2 failed caps, started retracing my steps and found my error measuring the original. Still have the NOS part in a relatively shiny can w/label, orig box etc.

marv

:I have to admit that I rarely listen to the AM dial anymore. It is a tragedy. I hardly ever use my 8 tube car radio anymore, even though it is such a fine performer. I truly do enjoy the silence in my car, especially since there is no melodic and enjoyable music to listen to on the AM dial (except on occasion, when I can get 740 Toronto, and that music is sketchy).
:
:However, until very recently, I'd feed classical music and good jazz from the FM dial into my radios via transmitter or wire to the amplifier. I still feed them with CDs, and now I found a good classical station in South Carolina (or was it North? I forgot.) that has on-line transmissions (not the best fidelity, but it won't be noticed over my radios). When there IS good music to listen to, I run my radios a lot. I don't just turn them on to listen to whatever noise there is on the dial. My Silvertone phonograph usually gets a lot of use, too. I have a huge collection of 78s, though strangely enough I have heard all of them too many times. It is too bad that 78s aren't as convenient as MP3s or CDs, or else I'd have more than 1000. If I had more than 1000 78s, though, I'd fall through the floor.
:
:At any rate, if you do have a ton of radios, and don't have time to put a lot of listening into each one of them, then you surely will not be able to test re-formed electrolytics. Also, for a huge collection, it isn't worth the time. It is an interesting experience, though, and I have been successful about half of the time with the process. I say that if you're curious about the idea, you should at least give it a shot several times. Don't necessarily make a routine out of it unless you have so much time to kill (I used to, but I moved out, and I go to school, and I work, so I don't really have much time for anything except listening to the radios I own that already do work....there are others that are patiently waiting for the day that I may have a lot of spare time on my hands).

Usually if you run NOS caps for at least an hour, they come back to life (in my experience). Start out at a lower voltage and work your way up. Observe current draw. With electrolytics rated around 200 WVDC, I've simply reformed them on my tube tester by wiring them through a rectifier tube, and then observing the meter reading. As it went down, the electrolytic re-formed. I used the #4 setting on my EICO 625. Of course this is not practical with all electrolytics, as you have only a couple of voltages to choose from, and can be hazardous to the tester. That is how I performed my most recent re-form, though. The electrolytic tested out highly leaky, and now works perfectly in my Majestic 180 (which I'm using right now). I started with lower voltages by reducing the rectifier filament voltage, as well as the 'line' adjuster.

A better method is with a power supply built specifically for the purpose, with many voltage options sent through a selector switch, a current meter for monitoring current, and a rheostat for varying current.

The biggest concern during re-form is current draw. You want the current draw to go down to practically nothing. If, after you reform the capacitor, you can't get accurate capacitance, the unit probably has dried up a bit. When re-forming, though, observe current draw.

T.

:Usually if you run NOS caps for at least an hour, they come back to life (in my experience). Start out at a lower voltage and work your way up. Observe current draw. With electrolytics rated around 200 WVDC, I've simply reformed them on my tube tester by wiring them through a rectifier tube, and then observing the meter reading. As it went down, the electrolytic re-formed. I used the #4 setting on my EICO 625. Of course this is not practical with all electrolytics, as you have only a couple of voltages to choose from, and can be hazardous to the tester. That is how I performed my most recent re-form, though. The electrolytic tested out highly leaky, and now works perfectly in my Majestic 180 (which I'm using right now). I started with lower voltages by reducing the rectifier filament voltage, as well as the 'line' adjuster.
:
:A better method is with a power supply built specifically for the purpose, with many voltage options sent through a selector switch, a current meter for monitoring current, and a rheostat for varying current.
:
:The biggest concern during re-form is current draw. You want the current draw to go down to practically nothing. If, after you reform the capacitor, you can't get accurate capacitance, the unit probably has dried up a bit. When re-forming, though, observe current draw.
:
:T.

T.:
That's essentially what we did when I overhauled aircraft strobe lights. Some caps would work for thousands of hours, and others failed after a short time. Our thinking was: "If a cap has been working for X hundred hours and passes all the tests for a new one, why replace it?".
So what we did was measure the capacity (usually 275uF@450V) and then put the cap at full Voltage for an hour. If it didn't explode, and some did, then we put it back in the airplane, where it spent its life charging to about 375 Volts and down to about 75 once a second.
I know we are repairing radios, and not airplanes, but I would caution you to look at the current of your electrolytic, after being subjcted to full Voltage for a period of time.
Lewis