Opinions about longevity of oil-filled caps

[Ralph S]

I'm working on a piece of late 1940's television gear which is filled with Cornell Dubilier electrolytics which are the totally sealed, metal can types. These are the oil-filled caps in metal cans which are completely soldiered shut. My question is this: does anyone have an opinion on the lifespan of this type of cap. I've got a working iconoscope camera from 1943 in which I left this type of cap where necessary for physical reasons (mainly the video pre-amp.) I'm concerned about the current project simply because of function, reliability and physical difficulty of replacement. Any thoughts?

[Tom Albrecht]

Are you sure they are electrolytic? I'm aware of oil-filled paper caps, which are generally quite reliable and don't routinely need to be replaced. However, I'm not familiar with oil-filled electrolytic caps.

[walterbeers]

Oil filled caps are usually found as run or start capacitors on large motors, air conditioners, compressors, and refrigeration equipment. If you know the value and voltage you might be able to find replacements at appliance and HVAC supply places. I don't believe they are electrolytic and generally don't have any polarity. Yes, they do go bad, at least on AC units.

[peter scott]

Hi Ralph,

Check them for value and leakage and if they look anywhere near OK then they are probably reliable. In my experience they are pretty good.

Peter

[Ralph S]

So far the ones I've replaced are polarized, but after pulling the originals from service, I've found them to be right on value and I probably didn't need to replace them after all. They are in metal cans and completely sealed! You're right though, the values of these are in the non-electrolytic range, i.e., .25 @ 650vdc and a double such as 2 x .5 mfd at 600 vdc with a common ground. I suspect there are others which are much higher values, I just haven't gotten to them yet.

Thanks for the comments; keep them coming!

[bob91343]

As stated, they are reliable. When they fail, often as not it's just that they spring a leak and make an oily mess. That happened to my friend's HP410B voltmeter, an old version. The date marked was in the 1940s. The amazing thing was that I had the identical part in my junkbox, with a similar date. We installed it and all is well.

[M3-SRT8]

My experience is they are fairly reliable. Fairly, as in they usually work even after 60-plus years in the large DuMont televisions (er, telesets. Sorry, Balcom) that I restored.

But, they can fail. One of them failed in an RA-119A Royal Sovereign after @20 hours of use. It was the 1.75 MFD 850VAC in the main chassis. I replaced it with a couple of non-polarized oil filled NOS GE 3.5 MFD 440VAC in series.

That left the remaining 1.5 MFD 950 VAC oil filled in the HV chassis. Not wanting to tempt fate, replaced it with a pair of new C-D 3.0 MFD 660 VAC, again in series.