The AM Forum

I think I know the answer, but I’d like to have a few opinions.
I’m restoring some mid 1960’s Knight Kit gear. I expected that the multi-section caps in the power supply would need replacement. Guess what, they test perfect – value wise, leakage and low ESR. Given their age, I'm amazed! The previous owner told me that he used it regularly, so that might explain it.

Normally I’d gut the cans and restuff them with new smaller devices to retain the original look. Experience says replace them, but the opposing voice says, "if it isn’t broken, don’t fix it!"

I restored many tube radios (household, no ham). If they seem ok, I check with a IR that the temperature doesn't raise after half an hour operation. If no raise, no replace. Always worked for me. Don't forget to put a piece of tape at the cap, metal gives errors with a IR temp meter.

That's an interesting test, I'll add it to my check list. Thanks

If you are going through the trouble of restoration, go the distance.

Use some of those long life 105 C Nichicons or Panasonics.

I wish all hams that want to repair or restore their equipment could obtain results from component engineers about electrolytic caps.  It is generally acknowledged that the NASA space program led the way for more reliable components as a part of what they did for exploration.   The long and short of it is that the results for long lived electrolytics was known in the USA in the late 60's but the Japaneese really grabbed the bull by the horns in the 70's by their use of Juran and Deming quality control methods pioneered in (you got it) the USA.  unless the cap is marked long life or computer grade or similar it generally will be failure prone after 11 years.   longer than that is iffy and problematical.  I have seen premium Japaneese caps last 50 years.  Its all about purity.   

Very interesting - I work for Panasonic, actually started in the components division (38 yrs ago) and I now realize that we made some pretty decent caps. I have a few Ni-Cad batteries that still have the National name and they still hold a charge after 35 years. They were rated at 450 mah, at last check they are about 300 mah.

Penny Wise, Pound Foolish. A smoked power transformer is always a possibility. I always go new it is cheaper and more dependable in the long run.

John N8QPC

Agreed.

I usually test by simply applying a current limited voltage near the ratings of the caps and check the current after ten or fifteen minutes.  I have a lot of communications and test gear thats 50, 60 years old that still have the original electrolytics.

There are voltage versus leakage current charts available on line, and although they vary somewhat, you can determine a "reasonable value" by some comparison.  Charts usually show Maximum Allowable, so values of 20 to 30 percent of those listed would be what I'd consider usable.

Keep in mind that electrolytics made in the 60s had 2 to perhaps 4 times the leakage currents of caps manufactured today.   

The type of product you find the caps in also has a definite impact on quality.   The cap found in a 1955 $19  AA5 radio, was no where near the quality of one found in a piece of $1200 GR or HP test equipment.

If the original caps check good and you use the equipment regularly, then check them again in a year or so.  You may find leakage has increased enough to warrant replacement.

Agreed + 1.

There are two kinds of old electolytics -- those that are bad,  or those that will go bad and take something made of unobtanium with them when the fail.

Pay me now, pay me later.   But you will pay.

Task completed - replaced them all! Now, will it last another 50+ years? They might, I won't!

While the issue has been resolved, I wanted to point out that bad caps that are visible, such as above-chassis mounted, are often left in place to maintain original aesthetics with the new caps mounted out of sight under the chassis.

Conversely, I've heard stories about purists who search at length for exact replacements, but what they end up with is a cap with a short life span.

When I restored radios of the 1920 - 1930 's, many were bad, even radios with the wet type. Indeed for aesthetic reasons, replacement or modern caps underneath was not possible, so in general I ended up opening the cap and removing the guts. Than put the new cap inside the old housing. Also the most 1920 radios had leaking caps, the metal encapsulated block type or a glass tube closed with tar. Also these had to be "operated". Sometimes purist freeze them for a while what seem to lower the leaking current substantially. I prefer operation and renewal of the interior.

hi John ... as I have said before add a fuse to EACH power transformer to prevent stinky smoke signals

A common newbie mistake is to solder a new cap in parallel with the bad (Or one day to be bad) old cap.  No dice!

The old cap must go away.  Its case may remain, but the old cap must go.