I was looking at Partsconnexion’s sale of the Audio Note silver foil capacitors with Mylar dielectric. At $640 (before discount) per for the 1 mF/630v specimen these are expensive. Made me wonder why they used Mylar, rather than polypropylene, polystyrene or PTFE, in that order of reported improvement, which are widely manufactured.
The text on Partsconnexion talks about the balance between performance and reliabilty, but since many caps are successfully manufactured with these “better” dielectrics I am left puzzled.
Audio Note Capacitor 1uF 600Vdc Silver Foil
The text on Partsconnexion talks about the balance between performance and reliabilty, but since many caps are successfully manufactured with these “better” dielectrics I am left puzzled.
Audio Note Capacitor 1uF 600Vdc Silver Foil
Even more markup to rip off the snake oil victims, surely? After all they use vegetable oil, how cheapskate is that - the stuff is not stable.
BTW how come a plastic film capacitor has oil in it at all?
How come an audio capacitor needs litz wire leads?
Nothing to do with audio engineering, everything to do with ruthlessly exploiting the gullible, and wasting valuable metals, come to that.
Paper in oil was used as a dielectric before plastics were invented; they used what they had. Paper is an awful dielectric on its own, but oil improved it. The resulting caps were leaky and mostly unreliable, but that was the state of the art 70 years ago.
Modern plastic dielectrics are much better so going backwards is plain daft. No need to add oil; that is just an efficient way of extracting money from certain audiophiles.
No need for silver or litz wire; again this is economics not physics.
Modern plastic dielectrics are much better so going backwards is plain daft. No need to add oil; that is just an efficient way of extracting money from certain audiophiles.
No need for silver or litz wire; again this is economics not physics.
Arguably: the oil is the dielectric, the paper is just a mechanical separator. Obviously they are so commingled that they have to be considered together.
An advantage of oil is that after a breakdown, fresh oil seeps in and the gross damage is "repaired". But the zap releases gas and metallic byproducts, and eventually the cap is kaput.
A real problem with oil is that it is best when DRY. This is a wet planet and oil gets moisture in it. This reduces its breakdown voltage. Also increases breakdown of the paper.
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/defau...isture in Tranformer Oil Behavior Webinar.pdf
House-size utility transformers are fairly well sealed and over-spaced so they do not need the DRYest oil, but this is one reason why pole-pigs overheat and burn after 20-30 years.
Radio-size capacitors can't even try to be sealed. Humidity never sleeps, seals weep, and the high surface/volume ratio means a lot of seepage for the oil inside. Also the narrow separation of 400V caps means hardly any "repair" after a breakdown, and no place for metallic zap-crap to fall out.
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.
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.
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.
Expectation bias of course. Polypropylene caps better than mylar, so using mylar is perverse. Some people like perverse I guess.
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.
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.
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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?
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
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