PIO cap ??

[NOSValves]

By the way it is very easy to confirm what type film/paper your dealing with if you are lucky enough to be able to separate the layers.. Simply put a flame to it and see how it burns...if its paper it will leave paper like ashes and not burn with a melting action. If its some type of film it will smoke a good bit and melt while it burns..........

 

[Pio1980]

The bursting has nothing to do with oil. Cut one apart and find the oil.... they are petrified inside and when they start to short they swell and crack open....I've pulled thousands of them out of gear over the years from countless manufacturers and never found a drop of oil or paper for that matter...

Interesting. To what would you account their high failure rate? I'm not being argumentative, I'm interested in your experience and observations for general education of us all in a collaborative manner..
IIRC, paper/organic oil caps can have a distinctive odor when cut open.

 

[audiodon]

This post is not directly related to the subject of PIO caps, but gives a decent comment on cap construction in the mid-late 50s period.
These are foil and oil with beeswax caps, unrolled and deconstructed for your viewing pleasure. This particular post was about "should the shield point towards the source". It is relevant to this discussion on how caps were constructed back in the day though.
http://www.audiokarma.org/forums/showpost.php?p=6686022&postcount=66

 

[Pio1980]

This post is not directly related to the subject of PIO caps, but gives a decent comment on cap construction in the mid-late 50s period.
These are foil and oil with beeswax caps, unrolled and deconstructed for your viewing pleasure. This particular post was about "should the shield point towards the source". It is relevant to this discussion on how caps were constructed back in the day though.
http://www.audiokarma.org/forums/showpost.php?p=6686022&postcount=66

The banded end was the "shield"/grounded end with the outer foil wrap the 'shield'. As a coupling/blocking cap the banded end went to the output of the proceeding stage.

 

[audiodon]

Yes, you are correct. I could have explained it better.

 

[Pio1980]

FWIW, the only plastic cap failure trends I am aware involved certain ERO plastic film caps with eventual interface problems between the wire lead and the foils. It's possible that older Conrad-Johnson products with the custom-made caps may also have this problem, check with C-J if you are concerned with this.

 

[Pio1980]

Yes, you are correct. I could have explained it better.

You did fine, I just riffed on your contribution.

 

[diamondsouled]

I've got a collection of Sprague catalogues going back to 1937 and up to the 1980's, don't have all the years. Here's a few scans. The first two are from from 1951, they were already calling them Black Beauties, but they were branded: Telecap, before the 160P type part number started being used. These caps were oil impregnated, molded in Bakelite phenolic. By 1957 the Black Beauty name was out front and the Telecap name came second. The second and third scans are from 1960, still before the 160P part designation. They had two lines, one with a solid, polymerizing, impregnate - Difilm Black Beauty, and one that was paper/mineral oil impregnated. To complicate things they called them both Black Beauties the second line called - Mineral-Oil Black Beauty - only available in high voltage as far as I know 1600V +, By 1970 they had dropped the Mineral-Oil Black Beauties and only have the Difilm solid impregnate Black Beauties. They had begun using the 160P part designation by then. Somewhere in there they went from Bakelite to plastic molding I believe, not sure exactly when though, they say "tough" but they don't say what it is.

Hope this clarifies things a bit lol.

 

[ConradH]

By the way it is very easy to confirm what type film/paper your dealing with if you are lucky enough to be able to separate the layers.. Simply put a flame to it and see how it burns...if its paper it will leave paper like ashes and not burn with a melting action. If its some type of film it will smoke a good bit and melt while it burns..........

+1 IMO, you can't argue with a good test. Don't breath the fumes though! The caps I was thinking of were indeed the Black Beauties and Bumble-bee caps. Everybody says they're PIO but I've never opened one up. I did recently repair a 1960s guitar amp and the caps were plainly marked "oil", though they looked more like conventional axial aluminum electrolytics. Every one was bad- values low, values high and high DC leakage. The big question, if the black plastic caps were film, why the high failures?

edit- just saw the catalog pages- thanks!

 

[Pio1980]

Oily paper caps were used for the HV dynode blocking couplers in the 1940s electrostatically deflected TVs and IME they all fail. I have one Motorola 7" electrostat with all-stock caps thru-out that I will leave as-is for historical interest.

 

[sony6060]

Somebody, here probably, said the trouble with the old PIO caps had to do with the paper. It was bleached or something, which left it acidic, and accelerated the deterioration. That was a huge issue with archivally processing and mounting photos and artwork- acid free paper required, so it's not surprising it applies to capacitors too. Capacitor life, especially for aluminum electrolytics, is highly dependent on material purity. It can make the difference between weeks and decades.

The oldest performing PIO caps I owned was in a power supply that powered a Hammarlund 210X receiver from approximately 1936-37 era.

 

[Pio1980]

The oldest performing PIO caps I owned was in a power supply that powered a Hammarlund 210X receiver from approximately 1936-37 era.

Mine looks like this with the big square can oily caps;

So, is somebody going to tell us what the common failure mode of bakelite encased tubular caps would be if they are not PIO?