PIO cap ??

[ferninando]

Am I correct to assume that the paper in a PIO cap is the dielectric material, soaked in oil? Rather than a poly material?
Just curious as to what makes them so sought after.
I have some and may in future use some in my HF85 rebuild.
Thanks

 

[Gang-Twanger]

Well, people argue back and forth about cap types and hi-fi gear and whether oil caps have a certain special "something" about them (and I wish I knew what part/s makes them sound different), but for the cap I have wired to the tone pot of my guitar, the PIO I use has a much-more-open and musical sound than the orange drop I have wired next to it, which is a bit tighter in it's attack but sounds constricted in comparison to the PIO (I have both caps wired to the tone pot at the same time, with a push/pull knob to choose between them, but I usually use the PIO... Tried a bunch of different ones and settled on those two). I wish I understood the specifics of it, but there's definitely a difference in some circuits. I have to assume the differences are most-noticeable with gear from the tube-era where PIO's were most-common and probably not as noticeable with modern gear, but that's just a guess.

 

[ferninando]

thanks gang,but (Im not concerned about sound of a pio cap , I want to know about the material of the dielectric, pio, paper soaked in oil. I heard all the kudos of their sound qualities till I cant stand it anylonger. not really but you get my meaning.
And what you say is true, in fact I got a bunch of em from a ebayr of tone caps for the git folks at a good sale price free shipping. 8 .1uf and 8 .047. just to have some to use sometime or swap some of what I have in other amps to see if theres a difference I can hear.

 

[ConradH]

The oil is probably more of the dielectric than the paper, but they both contribute. Certainly sought after by some, but the old black plastic ones were notoriously unreliable. The rest weren't notorious, but still unreliable. They develop high DC leakage that causes havoc with tube circuits. Other than the boutique market, and some very high voltage or AC caps, there's little production of small PIO caps.

 

[ferninando]

dont care about old crap. just the new stuff. its all I play with .
so it IS the oil thats the dielectric then and the paper is just a separator of the capacitor plates. sounds good to me . no further input required.
Thanks all.

 

[battradio]

I would suggest you cut one open and see what its made out of , the Russian ones are most likely paper . The very expensive one are most likely a plastic film and oil cap . Too me the paper and oil caps blur the high end and make a warm fuzzy sounding amp , masking transients .
It appears the Jensens have paper in them also .Plastic cap used to make mylar and oil caps that were in a lot of radars I used to work on .

 

[sony6060]

Paper & oil is a PIO capacitor. Oil is a good dielectric and oil is not required with poly type capacitors.

 

[ferninando]

I am NOT going to cut open and expensive russian cap just see whats inside!!!!
I know whats there. oil and paper. oil is the dielectric and paper is the carrier of the oil.
mystery sovled.
thanks all for comments.

 

[GAryB]

There is an interesting paper on why capacitors sound different on the Audience website http://www.audience-av.com/capacitors/a_chemistview.html

Here's a quote of the material relevant to PIO caps:
"Up to this point, I have only mentioned in passing paper/oil (paper-in-oil) capacitors. These classic devices from "days of yore" are making a comeback in some audio circles - especially among tube connoisseurs. Certainly, they are of interest. Unfortunately, they employ a composite dielectric that consists of a paper spacer/absorbent saturated with an oil; therefore, they do not readily lend themselves to the present simple analysis. Since the dielectric polarization primarily occurs on the surface of the dielectric material, in the vicinity of the plates, the dielectric constant in such a capacitor would consist of a weighted average of two dielectric constants: the most significant weighting attributed to the oil and the lesser weighting attributed to the surface area of the fibrules of paper in contact with the metal plates."

---Gary

 

[Pio1980]

It's just oily paper, before reliable plastic film the best dielectric construction for an economical somewhat compact-for-capacity cap if not the longest-lived. The oil can and does deteriorate in the presence of air and moisture and then that's pretty much it. It can also swell and crack or burst a Bakelite casing in the course of aging and then that's that.

 

[datafone]

"expensive russian cap"

Wow, I have never seen one of these, but I have seen plenty of cheap as chips ones, in fact I chucked some out the other day.

 

[Pio1980]

"expensive russian cap"

Wow, I have never seen one of these, but I have seen plenty of cheap as chips ones, in fact I chucked some out the other day.

Word is out, prices went up. I'll stick with plastic film here.

 

[Gang-Twanger]

One thing I've been wondering is whether it's the USE that makes a cap finally go bad or if it's just a simple matter of time, whether the cap was used in a circuit or not. I have to assume it's the use that does it (use over a long period of time), but you know what they say about assuming...

 

[Pio1980]

Seems to be primarily age tho heat and voltage stress will accelerate whatever deterioration takes place. They can go bad NOS on the shelf in time.

Sent from my SCH-I605 using Tapatalk 4

 

[battradio]

Paper & oil is a PIO capacitor. Oil is a good dielectric and oil is not required with poly type capacitors.

Plastic and oil is used in high voltage application's , it keeps the moisture out at the end where it can arc over .

http://www.plasticcapacitors.com/product_index.html

 

[ConradH]

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.

 

[NOSValves]

The oil is probably more of the dielectric than the paper, but they both contribute. Certainly sought after by some, but the old black plastic ones were notoriously unreliable. The rest weren't notorious, but still unreliable. They develop high DC leakage that causes havoc with tube circuits. Other than the boutique market, and some very high voltage or AC caps, there's little production of small PIO caps.

Internet myth # 432...the black plastic encased vintage caps were not PIO caps. They were Mylar film and foil.....the Hi Fi industry pretty much stopped using consumer level PIO cap in the 1950's because of the extreme failure rates and the tendencies to leak DC voltage, after all blocking DC voltage is the main function of an interstage coupling cap. The Military versions of PIO caps US , Europe and Russian usually are metal encased and hermetically sealed which is much higher quality construction then the consumer level PIO caps of the 50's and 60's.........."HIGH QUALITY" Mylar Film and Foil ruled the day in the golden age of tube Hi Fi.

 

[NOSValves]

I am NOT going to cut open and expensive russian cap just see whats inside!!!!
I know whats there. oil and paper. oil is the dielectric and paper is the carrier of the oil.
mystery sovled.
thanks all for comments.

Expensive??? Those are not expensive by any stretch of the imagination if compared to any modern made PIO cap.... These are very old by the way most made in the 1980's before the Russian empire came tumbling down. BE very careful using them you should have a cap analyzer that can test under full rated voltage to check for leakage. They do have issues after 30+ years...the date codes are right on them.

I have cut apart every possible Russian made cap! Some are PIO, some are film foil with oil, Some are paper and foil...some are Teflon film and foil. All of them are high quality but they should be tested before placed in service IMHO.

I used 1000's of these caps when they could be bought in high numbers back in the early 2K's I also tossed 100's of them in the garbage.... KW Tubes was my main source long before these were available on eBay. I learned about them from my father who learned of them VIA Ham radio guys directly from Russia..........those were the days.

 

[Pio1980]

Internet myth # 432...the black plastic encased vintage caps were not PIO caps. They were Mylar film and foil.....the Hi Fi industry pretty much stopped using consumer level PIO cap in the 1950's because of the extreme failure rates and the tendencies to leak DC voltage, after all blocking DC voltage is the main function of an interstage coupling cap. The Military versions of PIO caps US , Europe and Russian usually are metal encased and hermetically sealed which is much higher quality construction then the consumer level PIO caps of the 50's and 60's.........."HIGH QUALITY" Mylar Film and Foil ruled the day in the golden age of tube Hi Fi.

Um, I don't think that is entirely accurate. The Sprague 160P Red Letter caps are Mylar, the stripe-coded so-called "bumble-bee black beauties of death" are generally PIO and also prone to bursting as well as electrical leakage IME. Any other plastic cased cap not known to be plastic film is suspect for leakage until proven otherwise at max rated voltage.

 

[NOSValves]

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...