That's true - I barely found them to be defective.
I think that some of them were Pale Green, and others Brown-Orange, in the same era, but I don't know who produced them, though... Possibly Italian too : Ducati ? Mial ? Under license ?
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I have several cartons of Russian PIO caps that are glass sealed. They are all in sealed cartons brand new. Would these caps be good for coupling capacitors in pre-amps and tube amps. Would they also be good as bypass caps for electrolytics?
Any comments and suggestions would be greatly appreciated. thanks in advance.
Any comments and suggestions would be greatly appreciated. thanks in advance.
Short of leaking, PIO (paper & Oil) do not dry out. They are fully impregnated with one of several types of oil. Such as mineral, silicone, or other variations. Depending on the stress across the capacitor, they can fail with time.
Any Vintage caps have a cult like following, such as Bumblebee, Black Beauty, and Mustard. Also throw in Astron brand parts.
Yes - the Astrons are very sought after for Fender amps. Counterfeiting and faking has hit the bumblebee market.
Even if one discounts the perceived differences in sound with these vintage caps, the vintage collectors want to see original style caps in the amps.
Even if one discounts the perceived differences in sound with these vintage caps, the vintage collectors want to see original style caps in the amps.
I know of a few places selling bumblebee clones, one (Jupiter) has been reverse engineered using the same materials, in a more reliable configuration. Others are just PIO masquerading as the originals.
Being in the capacitor industry for 43 years this May (2024), not a lot has changed in the technology. Bumblebee caps were polyester with aluminum and/or tin foil with a particular impregnant. Some films have gone away, such as Polycarbonate, Polysulfone, Polystyrene (for the most part) and thin PTFE. There have been minor changes in materials and/or technology for metalized films, but for the most part has remained the same. That said, technology has allowed for the manufacture of thinner films, particularly polypropylene.
Yes! I miss the ready availability of polystyrenes, but am glad that polyprops are getting a bit smaller.
Great thing about polystyrene is the flat temperature coefficient between -50 C to 65 C, its literally in the +/- 50 PPM. About 15 years ago, the thinnest PP film you could get was 4um, now its down to 2.5um, approaching 2.0um.
PS capacitors have a linear tempco for their usable range, but it is negative, not flat: around -125ppm/°C typically.
See here for example:
https://www.acoa-capacitors.it/wp-content/uploads/pdf/polystyrene_V1.pdf
There are many other sources and tables available, and they all show similar figures
See here for example:
https://www.acoa-capacitors.it/wp-content/uploads/pdf/polystyrene_V1.pdf
There are many other sources and tables available, and they all show similar figures
Capman, would you happen to know the foil thicknesses/voltage relations for the different dieelctric materials?
Philips had a different type of construction (wrapped-end-filled), but they also quote the same value ( page 12):
https://docs.rs-online.com/030a/0900766b8002fb08.pdf
https://docs.rs-online.com/030a/0900766b8002fb08.pdf
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I disagree, Mil-C-19978 Characteristic P from 0 C (correction from -50 C) to 65 C is flat, 150ppm, +/- 50 ppm. I've been in this industry for 43 years, worked as a capacitor design engineer for 4 different companies, one was the leading US Military supplier for many many years. I also working in the materials industry for film extrusion and metalizers. I can tell you if the PS is annealed and stress relieved, its virtually flat TC. Honestly it doesn't matter, as they are not commercially available......
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In film/foil (or metalized) that is a complicated subject. Each dielectric has different withstands, with metalized being complete different. Actual application and life expectance play an important part of that. Often multi-layers of thinner materials are put together, say 4 x 6um will withstand more than 1 x 24um. Temperature also comes into play. As a rule of thumb, 300 - 600V/um while considering the parameters I listed above.
These are not the "Traditional" wound PS/Foil capacitors. Unfortunately I do not have my Mil spec's available.