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bigwill 25th August 2011 11:36 AM

I need some fairly specific capacitors types, like polyester or silva mica.
Normally this wouldn't be a problem, but I have some PCBs that dictate that I use axial capacitors in certain positions calling for a low value, the values being:

270pF (220 should do)
340pF (330 should do)
500pF (470 or 510 should do)

The 4700pF and 500pF need a voltage rating of 400v or more, whereas the rest can be rated at 125v or more.

I'm having great difficulty finding suitable parts that aren't ceramic or insanely expensive (1 per cap?)

Does anyone know where/if you can get these types at a reasonable price? NOS should be fine if I can buy a fairly large quantity.

Cassiel 25th August 2011 01:17 PM

I'm also looking for 330pf/500V and 100pf/500V 1% silver mica caps for a phono preamp. Don't care if they're expensive - I only need four.

TheGimp 25th August 2011 01:44 PM

Check fleabay. I got several batches of former Soviet Union Silver Mica caps at reasonable cost.

Like these 4700pF at 500V:

4700pF/500v./10% SGM-4 Silver Mica CAPACITORS (6pcx.) | eBay

No affiliation, blah, blah, blah....

jcx 25th August 2011 01:47 PM

if you're looking at NP0/C0G ceramic then they are superior on all measures to polyester, and if dielectric absorption is taken as a "audio quality" indicator they overlap with Silver Mica depending on manufacturer

polyproplylene is common and good, polystyrene would be most people's choice for RIAA filter

bigwill 25th August 2011 02:49 PM

I have no audiophool neurosis with using ceramic as long as they don't introduce measurable distortion

As long as they're axial and fit, I'm not too bothered :P

indianajo 25th August 2011 03:27 PM

Ive successfully used ceramic 4.7 uf coupler caps instead of grainy sounding (from the distributor that way) tantalum electrolytic caps. The caveat is I had a 1.6 V signal, and I used 50V caps. They are non-linear, but less so over only 1/25th of the curve.
That said, mica caps are available, I think from AZ, although it might have been IL. Antique radio parts houses specialize in these. There is another radio parts house in Canada, I haven't bought from them so I don't remember the url.

Rodeodave 25th August 2011 03:28 PM

Silver mica capacitors/Dipped silver mica


TheGimp 25th August 2011 03:28 PM

Avoid X7R and Z5U, they are microphonic due to the use of type 2 High-K dielectrics which are piezoelectric.

Why don't people use polystyrene for coupling?

Rodeodave 25th August 2011 03:51 PM


Originally Posted by TheGimp (

Why don't people use polystyrene for coupling?

Maybe because of their somewhat higher inductance and heat sensitivity? Not sure though...

Cassiel 25th August 2011 07:41 PM


Originally Posted by Rodeodave (

Thanks for the link. :)

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