current source for small caps

[tvrgeek]

Looking for Polystyrene or Polypro, from 33p up to 330 or so. About the only thing I find this small are silver mica. Onec upon a time they were though highly of. What is the current thinking and where can I get polystyrene caps this small? Mouser and Digikey seem to be a bust.

[dchisholm]

Yes, polystyrene dielectric creates a capacitor with excellent electrical performance in just about all areas, except physical size and operating temperature range.

A quick scan of the main-line capacitor manufacturers' catalog offerings shows that they no longer produce polystyrene capacitors. Supposedly, the major supplier(s) of capacitor-grade polystyrene film ceased manufacturing the material quite a few years ago. From time to time I stumble across blogs and web pages where individuals make various claims, including:

• Small-time capacitor manufacturers are producing polystyrene capacitors using film intended for other applications.
• Tons of polystyrene capacitor film were stockpiled by manufacturers and speculators before production ceased.
• Gray-market chemical companies in east Asia are producing polystyrene capacitor film.
• Specialty manufacturers will produce polystyrene capacitors on a special-order basis for customers with deep pockets (e.g., medical and aerospace).

As you might expect, nobody seems to have independent support or documentation for the claims.


Mouser catalogs polystyrene capacitors from "Xicon", covering the E24 value series from 100 pF to 10,000 pF. I have no idea about the lineage of these parts, or whether their performance is comparable to previous generations.


Dozens or hundreds of surplus dealers (like All Electronics), boutique vendors (Talon Electronics), and hobby suppliers seem to have NOS (new, old-stock) polystyrene capacitors in various values for sale. Asking prices range from a bit more than what you would have paid 15 or 20 years ago (after inflation adjustments), to 10 times that amount. It takes a fair amount of work with a search engine to find many of these sellers.


The "Film Capacitors" page at < http://my.execpc.com/~endlr/film.html > has information, and a list of possible suppliers, that may or may not be accurate.


Dale

[riddellsr]

Originally Posted by tvrgeek

Looking for Polystyrene or Polypro, from 33p up to 330 or so. About the only thing I find this small are silver mica. Onec upon a time they were though highly of. What is the current thinking and where can I get polystyrene caps this small? Mouser and Digikey seem to be a bust.

Parts Connexion seems to have a stock of smaller values of Polystyrene.
Parts ConneXion - The authority on hi-fi DIY parts and components

[riddellsr]

Originally Posted by riddellsr

Parts Connexion seems to have a stock of smaller values of Polystyrene.
Parts ConneXion - The authority on hi-fi DIY parts and components

Also Justradios on ebay

[tvrgeek]

Looks like I have to go for silver mica for the lower decade. (10 to 100p) Might be wise to pick up a few of the Mouser selection kits. ( 100p up) and watch the sale fliers.
Polypro seem to be only in the larger sizes. I guess that is what industry uses. Beats mylar.

[DF96]

For small values you may be able to use ceramic, provided it is C0G or NP0. Where in the range the switchover occurs to non-linear ceramics depends on the manufacturer, but you may be OK up to 100pF. Look for caps with a black band on top.

[RJM1]

I've always liked silver mica and wished they were cheaper in larger values.
See this discussion and make your own decision.
Capacitor sound quality, silver mica in particular

Especially for higher voltages.