I read with interest the different electrolytic capacitor approaches for restoring these sets. I was in the very beginning of a restoration on one, so I thought I would experiment some. I measured the electrolytic caps in my 630 and found them in this state:
Cap. val@volts Measured Val Measured ESR
C220 80@150 49 .84
40@450 33.4 3.94
10@450 9.1 1.84
C224 20@450 OPEN OPEN
80@340 OPEN OPEN
C221 40@450 40.6 .78
40@450 38.2 1.08
10@450 10.5 3.32
C225 250@10 OPEN OPEN
1000@16 OPEN OPEN
C222 80@450 59.6 .72
50@450 37.9 .99
C223 40@450 13.2 11.3
10@450 5.3 4.9
10@350 4.05 3.9

I built a computerized capacitor reformer based on my Sencore LC75 procedure along with tips from the pros here in the forums. I tried reforming C223 but it could not reach its working voltage at low leakage. I ended up restuffing C224, C225, and C223 and reformed C220, C221, and C222. I also replaced all of the paper caps and out of tolerance or open resistors. Attached are pictures of the set, original wiring including old fixes, the cap reformer in action, the recapped set wiring, and a test pattern with the set using the three reformed electrolytics.

With the set operating using the reformed caps, I measured the main supply voltages and also the amount of ripple on each:
Supply Measured AC Ripple
+275 272 110mV
+135 128.6 18mV
-2 -2.3 4.5mV
-18 -19.9 40mV
+300 298.4 8.07V
+280 278 131mV
+350 331 8.5V
-100 -101 112mV
This was with 120VAC into the set.

To see what affect using all new caps in place of the electrolytics would make, I restuffed the three reformed caps. Before I removed the reformed caps, I made one last measurement of them with the Sencore LC75:
Cap Val@Volts Val ESR
C220 40@450 36.7 2.07
10@450 10.5 3.14
80@150 58.2 2.05
C221 40@450 42.3 2.08
40@450 39.2 2.36
10@450 11.1 3.95
C222 80@450 61.2 2.35
50@50 42.1 2.34

In the restuffing process I noticed that two of the three reformed caps had a very small(at most a dozen drops) of liquid electrolyte in them, while the third was barely moist. The three open/bad electrolytic caps that I restuffed earlier were all dry. Here are readings of the same supply voltages with the three reformed caps restuffed:
Supply Measured AC Ripple
+275 273.4 85mV
+135 129.4 12mV
-2 -2.3 1.2mV
-18 -19.9 13.4mV
+300 298.4 5.8V
+280 279.1 97mV
+350 331.8 8.4V
-100 -101 103mV
This was also with 120VAC into the set.

Attached is a picture of the same test pattern after the last electrolytics were restuffed. I can not see much, if any, difference even though the power supply ripple voltage are btter. The set does need a full alignment as the sound is weak and off frequency from the picture tuning.

I thought you have to do your ramble in one of these:
http://www.motorstown.com/images/amc-rambler-classic-03.jpg :D
AMC Rambler.

Anyway, I'd still use a fuse on the power transformer primary, just in case a reformed cap does eventually give out. Or even if a new cap dies...

Nice car! One of my other interests is restoring old cars. Here is a picture of my 1974 260Z that I finally finished last spring. :banana:

Dave

two of the three reformed caps had a very small(at most a dozen drops) of liquid electrolyte in them, while the third was barely moist. The three open/bad electrolytic caps that I restuffed earlier were all dry.It's my belief that moisture loss is a major cause of failure in old electrolytics. If you read up on old capacitor construction, you'll see that so-called "dry" electrolytics were only dry in comparison to earlier "wet" electrolytics that used a liquid electrolyte. Dry electrolytics used foil layers separated by paper impregnated with a moist paste or solution.

When the moisture seal on the bottom of the can fails, so does the cap, sooner or later.

Some people enjoy trying to salvage old electrolytics by reforming, but I don't have that much patience, and in my limited experience, there's no guarantee that a reformed 50- or 60-year old electrolytic will be reliable for the long haul.

Just my $0.02 . . . .

Phil Nelson

Some people enjoy trying to salvage old electrolytics by reforming, but I don't have that much patience, and in my limited experience, there's no guarantee that a reformed 50- or 60-year old electrolytic will be reliable for the long haul.

Just my $0.02 . . . .

Phil Nelson

I'm w/Phil...Yeah, you can "Re-Form" a cap, but I'd always be afraid of it, to me, its kind of a "Pet Sematary" resurrection...Why gamble an otherwise nice restoration on a few buck's worth of caps ?

I read with interest the different electrolytic capacitor approaches for restoring these sets. . . . . .

I built a computerized capacitor reformer based on my Sencore LC75 procedure along with tips from the pros here in the forums. .

OK, a couple of questions.

How long did the reformation process take on a typical electrolytic?

Was there a reason for not measuring the leakage of the reformed capacitor?


Comment:

I've never reformed a "dry" electrolytic, but have done the "wet" ones many times.

Many many years ago, the shop where I worked, found a small niche service of repairing 1930's radios and discovered that often the capacitors needed reforming.

We built an electrolytic reformer completely out of salvaged and scrap parts. We jokingly called a redneck reformer!

It was simply a small variac that feed a salvaged 325 volt transformer connected to opposite polarity diodes on each output. (The extra diode was because PIV rating could exceeded if one got careless.) It had a single 5 Mfd oil-filled cap to absorb some of the ripple and an surplus 0-500 DC voltmeter.

Inserted in the line between the variac and the transformer primary was a lamp socket with a 5 watt lamp that functioned as a current limiter.

We had a salvaged meter of unknown scale in series with the capacitor to be reformed. Across the meter was a wire wound pot. We calibrated that meter with the pot using a new electrolytic of the same value.

Our goal was to reform the old electrolytic to where it leaked no more than twice as much current as the new one and the electrolytic had to not heat excessively.

Depending on how long the radio had set unused, these took anywhere from 15 minutes to three days to reform. (We shut it down when no one was in the building so a day might be as little as 6 hours.)

If the capacitor shorted, it just lit the lamp and did no harm.

We could usually tell within one minute if the reforming was going to work. I do not remember any call backs from the owners of these radios for failed filter capacitors. We had a printed note with bill athat stated that the set should be run for at least one hour per month to keep it in operating condition. We stapled the carbon with their signature on it to our copy of the receipt.

James.

The reforming for each section of the three cans took different amounts of time. Some were quick, others longer. I used a current limit of 3 mA while the voltage was raised from zero to the working voltage of the capacitor. Then that voltage was held while the leakage current was watched until it got down to 200uA. The voltage was then lowered to zero. That cycle was repeated by the Arduino controller (until I checked back and saw several cycles had been completed). The first cycle always took the longest with the following cycles shortening. Most of the caps reformed in less than an hour. Two of the caps were completely open, so I did not reform them. One ran for two days without reaching its working voltage with the 3mA current limit.

From what I saw with this one set of 6 capacitors (too small a sample to make any general conclusions) I think reforming power supply capacitors might be ok if you want to take the chance (due to the desire for originality) and add a fuse. For my own restorations I prefer to replace all the electrolytics, and also add the fuse.

Dave

To do this as a fun experiment to see which caps could be revived , sure , I understand the "I wonder if I can" all too well . But , for any kind of continued longevity I gotta agree with Phil and Sandy and anyone else who said it ain't worth the long term risk of leavin em in there . New caps got 60 odd years in their favor as to running mortality .

If ya don't change em out , best not to leave the room while it's playing .....

I have repaired many old radio and television sets since the late sixties. I have generally found no problem reforming and repurposing old electrolytics. Paper capacitors leak and carbon resistors drift and need to be replaced but the electrolytics, especially the excellent Sprague and Mallory electrolytics from the 40's and 50's seem fine.

Most importantly, you can easily determine if the electrolytic will fail after reforming: simply bench test the set for a few hours and check if they get warm. I find that in 99% of successful reformings I have no problem.

I had my 16" 1949 RCA TV on this weekend for about six hours. It has probably run a couple of hundred hours and one section of a multisection capacitor opened. I replaced it with a NOS unit dated 1965 and the set runs excellently. Apart from that, all the rest of the electrolytics are original. And my 1948 RCA (my first set I acquired in 1969) has all original electrolytics and I have probably put a good thousand hours on that set over the years.

And my 1948 RCA (my first set I acquired in 1969) has all original electrolytics and I have probably put a good thousand hours on that set over the years.That's an interesting case, because one of my other superstitions about electrolytics is that they stay healthier when a set is used, rather than sitting idle for decades. In 1969, those caps were only 21 years old, and the set was presumably used during some of those preceding 21 years, so it hadn't been out of service for a super long time. Perhaps playing your TV periodically during the subsequent 44 years has helped those old caps beat the odds.

Phil Nelson

I too have been curious about the constant running of a set through its life and the effect on capacitor life.

When I got the set in 1969 and powered it up, I obviously then did not think of electrolytic capacitor age as a problem. The paper capacitors have over the years almost all have been replaced. But the electrolytics remain okay. (Funny, in 1969, a 21 year old 10" set looked really old: it is hard to recocile that a further 44 years has intervened).

My 1949 16" set with a KCS29 chassis, I got two years ago. The children of the original owner said it was retired to the basement in the early sixties and was not used. In fact it was only on the death of the parent and clearing out of the house that the set was uncovered. They said it must have sat unused for at least 45 years. Yet, apart from one section which opened up, the electrolytics recoved the capacitance and do not leak excessively (all electrolytics leak current).

One thing I have noticed for sure is if there is any sign of electrolyte leakage around a terminal or the capacitor seal, the capacitor must be replaced.