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Why Mylar in AN silver foil caps?
Why Mylar in AN silver foil caps?
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Old 13th September 2019, 04:40 AM   #11
Francois G is online now Francois G  United States
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PRR, thanks for you interesting post above. I have learned much from you over the years-thank you.

I appreciate all the insights and comments on my question. The consensus seems to be that the 1 micro F/630v Silver foil/Mylar+oil capacitor priced at $640 is mostly marketing hype and not needed for a prudent engineering solution. Thank you all.
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Old 13th September 2019, 07:42 AM   #12
Luke is offline Luke  New Zealand
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its 1uF not 1mF. I just dont get how there is a market for a $1K cap?
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Old 13th September 2019, 08:31 AM   #13
analog_sa is offline analog_sa  Europe
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Why Mylar in AN silver foil caps?
Quote:
Originally Posted by Mark Tillotson View Post

BTW how come a plastic film capacitor has oil in it at all?

Because of the self healing propertied when arcing. Plenty of industrial caps have oil, so no reason to act very surprised

In an audio cap it is mostly for the damping and its effect on cap sound. Some people love it.
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Old 13th September 2019, 11:03 AM   #14
DF96 is offline DF96  England
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Industrial caps may have to survive large voltage spikes. A coupling cap in an audio amp has a much more sheltered life. In most cases it will never see much more than half its rated voltage. The oil is mainly for marketing.
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Old 13th September 2019, 11:12 AM   #15
Mark Tillotson is offline Mark Tillotson
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Quote:
Originally Posted by analog_sa View Post
In an audio cap it is mostly for the damping and its effect on cap sound. Some people love it.
Expectation bias of course. Polypropylene caps better than mylar, so using mylar is perverse. Some people like perverse I guess.
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Old 13th September 2019, 12:21 PM   #16
RajkoM is offline RajkoM  Bosnia and Herzegovina
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Very informative posts from you PRR, as always. Thank you.

Long ago, when I was young, I made some linear amplifiers for ham radio. I used very, very NOS "Sic-Safco" oil capacitors (think 3 or 4 kV and 1 maybe 2 uF values). Russian oils caps too.
Today, 60-70 years of age these oil capacitors, they still work perfectly. Not perfectctly, but brilliant :-)

Looking for your next posts on DiyA forum.

Last edited by RajkoM; 13th September 2019 at 12:26 PM.
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Old 13th September 2019, 12:47 PM   #17
wiseoldtech is offline wiseoldtech  United States
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These so-called "superior" capacitors are as previously mentioned, merely Snake Oil for fools to buy and waste their money on.

And any seller/website that offers these types of things is one to run away fast from.
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Old 13th September 2019, 04:29 PM   #18
Francois G is online now Francois G  United States
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Quote:
Originally Posted by Luke View Post
its 1uF not 1mF.
My apologies for the typo 1 mF (in stead of 1µF) that many reacted to. Since I haven’t learned yet how to do a proper mu (µ) on my iPad, I meant to type mmF, like they used to do on typewriters in the old days, but missed the second “m”.

B.t.w. how do you all do µ (mu symbol copied here from a web search) and other scientific characters on an iPad?
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Old 13th September 2019, 04:36 PM   #19
billshurv is offline billshurv  United Kingdom
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Why Mylar in AN silver foil caps?
Quote:
Originally Posted by PRR View Post

MEGA-watt transformers, before they are put in service, or after long running, they wire reduced voltage into a short and let them heat-up for days to boil the moisture out of the oil, until oil tests show good results. (There are other methods, particularly to dry oil without taking the tranny out of service.)
https://www.vaisala.com/sites/defaul...%20Webinar.pdf

I did some work trying to automate large transformer maintenance scheduling as a lot of it is mandraulic and involves retying lab reports. Which is fine until something starts to go wrong then you only have a week or two between all ok and badaboom. luckily that is rare, but 'exciting' when it happens.


Edit: I remember now what they used. The 'Duval Triangle'. Really nice visual tool

Last edited by billshurv; 13th September 2019 at 04:42 PM.
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Old 13th September 2019, 04:56 PM   #20
RajkoM is offline RajkoM  Bosnia and Herzegovina
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µ is ALT together with 0181 (on numeric keyboard)

Ω is ALT and 234

etc... (search it on Google)

Last edited by RajkoM; 13th September 2019 at 05:03 PM.
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