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In Reply to: RE: Teflon capacitors posted by sser2 on April 25, 2017 at 21:28:02
There is a lot of confusion about Russian paper capacitors. For the most part it is due to great variety of types. Also, some capacitor types claimed by sellers to be paper-in-oil are not in fact paper in oil. Here are those that are true PIO:КБГ (KBG) types:
КБГ-МH (KBG-MN) Sealed in Normal metal case, foil electrodes
КБГ-МП (KBG-MP) Sealed in Flat metal case, foil electrodes
ОКБГ (OKBG) Special KBG, foil electrodes
КБГ-М1, M2 axial in metal cylindrical case with 1 or 2 insulated leads, foil electrodesCM (SM) Large transformer oil-filled capacitors, 3.5uF or 5uF
МБГЧ (MBGCh) Metallized paper for high frequency
K40У-9 PIO, foil electrodes
K42У-2 PIO, metallized paper. Technical sheet explicitly discourages their use for signal coupling
K75 PIO+mylar, most metallized, but some foil (K75-12)
Everything else is dry paper.
Dry paper with foil electrodes:
БМ (BM), БМT (BMT), БГ (BG), БГT (BGT), K40У-2, K40П, (K40P), K41.
Dry metallized paper:
MБМ (MBM), MБГ (MBG), MБГO (MBGO), MБГП (MBGP) MБГT (MBGT), MБГH (MBGN), MБГЦ (MBGTs). Everything that has "MБ" is metallized paper. Of newer types in this category is K42Ч-6.
Most paper caps have maximum temperature of 70C. Caps with letter T are good to 100C. Metallized paper capacitors have self-healing property: if insulation breaks down, metallization vaporizes locally, and insulation is restored. All metallized capacitors have a specific distortion called flicker. Metallization does not provide sheer metal layer, microscopically it is rather spots and patches with imperfect contacts between them. Voltage increase improves the contacts and effectively increases the area of metal electrode. Thus, capacity increases ( or "flickers") with voltage. The magnitude of this effect is not very strong, but sufficient to cause audible distortion.
Edits: 04/26/17 05/09/17Follow Ups:
Thanks so much for the great info on the Russian caps. I've had a lot of experience with them, and cut quite a few apart, but definitely had some knowledge gaps that you helped fill. I'm copying these posts, and storing them on my hard drive for reference. BTW when referring to the OKBG "special" caps do you have any idea how they are special, and how they differ from the regular KBGs?
twystd
but could not find more specific information. "Special" might be versions to accommodate specific needs of certain end users, for example anti-corrosion paint. It might also mean deviation from ГОСТ (GOST, State Standard). GOST, which was country's manufacturing law, described specifications in minute detail. Any deviation from GOST required special approvals.
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