Silver Mica treble cap problems.

[M Fowler]

Anyone else having SM 250pf cap problems such as leaking DC?

Three amps now have had scratchy pots and traced back to that pesky SM 250pf SM treble cap.

In all of them I replaced with Sozo cap.

Mark

[Jered]

I recently had that problem with a 500pf silver mica.

[frankdrebin]

me too,in the tonestack after a cathode follower,in the end i prefer the ceramic sound anyway

[TUBEDUDE]

I think they have issues when they get heated during soldering.

[Colossal]

Last one I had go bad was in someone's amp. It put DC on the volume pot. I am using those 1000V Sozos now or ceramic

[M Fowler]

I ordered a bunch of those Sozo 1000v 500pf and 250pf caps. I have been using them in every amp I build where the caps of those values were needed.

[tubesinside]

yes.....lots of trouble after about a year in use in the tonestack. Don't use them any more and I swap them out when amps come back in for service.

[oj]

Yes SM are very secretive, to heat or dropping .
Recoil a AC30 many year ago , that was fine when back plat was gone, but not when is was back on, do to heat.

[RockinRocket]

What brand of silver micas were you fellas having trouble with? The black, generic, cheap sub 1$ ones we find at all the amp building sites?

[ZMoney]

Has anyone tried using Polypropylene capacitor in that position? Seems To be cheaper and more reliable.

Some examples:
https://www.mouser.com/ProductDetail/Vi ... 5B%2FrE%3D

https://www.mouser.com/ProductDetail/WI ... x9JyvDo%3D

https://www.mouser.com/ProductDetail/KE ... lCn83v4%3D

[ngw]

I mostly use polystyrene for treble caps and haven't had any problems.
I recently bought some polypropylene ones (Vishay 1839) to try and so far they are working well also.

[JD0x0]

I mostly use polystyrene for treble caps and haven't had any problems.
I recently bought some polypropylene ones (Vishay 1839) to try and so far they are working well also.

Me too, and I prefer their sound, but you do need to be extra careful about heating them. It's easy to damage them with heat, but aside from that, they have great qualities for passing audio. I find them a bit less fatiguing in the highs compared to SM, but smoother than ceramics ive tried.


The SM I do have are NOS CDE's and I haven't had issues with them at all.

[guitarmike2107]

Interesting reading this, makes me wonder what the failure mode is.

On some caps if you bend the leads right at the body you can see the outer coating crack around the legs, I wonder if this is letting in moisture??

Or if the caps have just not been up for the job

[M Fowler]

Replaced another SM in a Rocket combo 2 days ago.