Your thoughts on PIO caps?

[5v333]

Good to know!
Also about dielectric absorbtion, have to dive in to it a little.

I have made a little listening tests with different caps in different circuits.
Generaly i think that different caps has the most effect in feedback loops.
Anything from feedback compensation to filter nets.

I do fancy film/foil stuff and low inductive stuff.
Havnt tried pape in oil yet. Hope that day will come.

 

[Whoops]

tryin to avoid starting a new topic,
does anybody have experience 'reforming' pio caps?--if thats even what is going on here

I've seen people in the past reforming NOS electrolytic capacitors but not old PIO capacitors were most people tend to suggest staying away from nowadays.

from different sources:

"Capacitors companies used the best technology that they had. But many factors enter into the scenario. Moisture is one factor. But the real problem is that the process used to make the paper was a problem. The chemistry used deteriorates over time creating its own acid which breakes down the paper even more. (Kinda like a breeder reactor). So, even the holy grail PIO (paper in oil) capacitors are not immune. The glass seal helps but isn't the answer The paper itself is the problem."

"Over time, they become more like a high value resistor than a capacitor and start leaking DC. If they are actually some material other than paper they might be OK"

"Old paper/wax capacitors are one of the most unreliable parts in an old radio. Don't let "molded" paper capacitors fool you. They are just paper capacitors in plastic cases and are just as unreliable as the ones coated in wax. Molded paper caps were sold under trade-names such as Bumble Bee, Black Cats, Black Beauty, Pyamid, Goodall, etc."

 

[volker]

After shabtek's post I measured several of my green and silver russian ones. Capacitance is spot on for each one, leakage is in the low nA range without any sort of reforming taking place. The resulting isolation resistance is in the 100s of Megaohms, which is on par with modern film capacitors.

 

[Kingston]

I have a rather large amount of soviet union PIO caps. These are roughly from the seventies. Their capacitance is also spot on and do not change after years of use in tube gear with significant heat involved. These are all hermetically sealed and as far as I know designed for even fighter jet radio and radar use.

Type examples that you can still probably find on ebay if the modern Russians have not completely decimated the old-world soviet warehouses located in Ukraine/Donbass region yet:
K40Y-9
K42Y-2
K73N-2
K75-10
MBG4-1
MBGCH

 

[Whoops]

does the risk involved really surpasses the easy to get high quality film capacitors we have available nowadays?

 

[Kingston]

does the risk involved really surpasses the easy to get high quality film capacitors we have available nowadays?

I take it you mean the risk of not being able to source these superior military caps?

 

[Gus]

What oil(s) is used?

 

[Pip]

In a lot of the NOS caps it is PCB's yes those PCB's! The newer ones use Non-PCB oils usually with a high flashpoint due to fire and expansion issues. It is hard to find the actual oil type info as it seems guarded IME.

Thus how they are sealed is quite important!

 

[Whoops]

I take it you mean the risk of not being able to source these superior military caps?

The risk of being or starting to be unreliable after to many years.

when you say superior you are comparing it to what?
are they superior to what capacitors?
and why are those capacitors superior in your personal opinion?