Silver Mica caps VS Polystyrene caps

[mcp]

Here's a simple experiment where any forum members can try. Take a power amp, replace the feedback cap with a ceramic and listen to the amp. Take note of the mids and highs. Then replace it with a silver mica.

BTW make sure the caps are the same values as the original.

[AKSA]

Graham (Circlotron),

Interesting info on the silver micas. I like 'em.

Very nice likeness on your avatar!

Cheers,

Hugh

[sam9]

I think I recall from somewhere that the principle application of silver mica caps is in thr RF industry. That would seem consistent with Circlotron's post.

[richwalters]

Nice to hear Silvered Mica still in active audio despite being far more expensive than polystyrene. Despite most of the "plusses" going to both types, I've repaired too many crowded amp chassis where users have complained of flagging power output leading to tube meltdown. PLEA.... don't solder polystyrene direct to the tube sockets i.e a-g2 via damper resistor for stability where a KT88 is blazing above in UL class A........the heat will eventually lead to cap failure and tube meltdown.
Check the upper temp ratings of polystyrene.......some types are quite restrictive,whereas mica excels.
Now do the sums...we've had 35°C ambient this summer, some polystyrenes upper limit is only 70°C, that allows 35°C rise on a tube pin quite likely.att'n:

[haldor]

Might also have something to do with the fact that silver mica caps with larger than 1 nF are just about impossible to find. That would tend to limit their use in audio.

Phil

[jean-paul]

Strange enough I can get Richard Jahre 32.4 nF 125 V silver mica caps more easily than I can find polystyrene caps ...

This reminds me of someone on this forum that claimed all low voltage silver mica's have to be tested before being used as reliability seems to be an issue. When I don't forget I'll search tomorrow for that.

IIRC it had something to do with the way the leads are connected to the mica ( mechanical stability ). When sealed with resin the caps should be better in that aspect.

[SY]

I've used both silver mica and polystyrene caps in tube preamps (for RIAA eq and RF suppression) and power amps (compensation cap). If there was any sonic difference, it escaped me. Reliability points strongly in the direction of silver micas. Never lost one, whereas I've replaced bunches of polystyrenes that went to join Jesus.

If you want to be ultra-cool, use the old flat-pack silver micas with the six dot color code.

[jean-paul]

I've replaced bunches of polystyrenes that went to join Jesus.

Didn't know He was into caps too.

Did the polystyrenes fail from overheating or what ? I never had one that failed till now ( knock knock on table ). I used NSF of german origin mostly. Never liked the english ( forgot the brand, sorry ) polystyrenes with the ultrathin wires as they suffered from overheating quite fast.

To make things even more unclear here were polypropylene caps from Siemens sold as polystyrene caps. Even a trained eye couldn't see the difference. Fortunately they were OK both soundwise and technically.

[SY]

It's a combination of heat and voltage, I'd suspect. I'll bet the rated WVDC is degraded quite a bit in a 50-75° C environment.

[jean-paul]

I only used them in relative cool ( both meanings ) solid state equipment, maybe that's why they didn't fail more than other caps. I had my share with electrolytics in Quad amps, but that's another story.