[Boatanchors] micamold caps

[Al Klase]

Rob and Joe,

I was going to echo what Joe said, as I've replace a lot of Micamolds, 
generally .01's. and they were paper and monumentally leaky.

However, I just pulled a .01 Micamold out of a BC-224H.  I restored the 
set years ago and cut these caps dead, leaving them on the back of the 
terminal boards, and installing, new mylars on the front side.  
Surprisingly, this cap indicated no leakage, and breaking it open 
revealed mica construction as Rob described.  This cap is chocolate 
brown, 1" x 5/8" x 3/8", and has square corners.

The bad guys, that I remember in numerous radios, were black and had 
beveled corners.
Like this:  http://www.antiqueradio.org/art/MicamoldCapacitor.jpg

The smaller values, say <1000pF, are almost certainly micas, and they 
are often in frequency determining circuits.  Leave them alone unless 
they prove to be defective.

The higher values, the ones used for bypass and audio coupling, are 
suspect.  I guess I'd cut one out of any particular set, and bust it 
open.  The paper units will be wound rather than stacked, and I'll bet 
the paper is brown after 70+ years.  Replace the paper caps before you 
even turn the radio on, and save a lot of troubleshooting and possible 
damage!

YMMV,
Al

Al Klase – N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/

On 3/21/2016 8:44 PM, Joe Connor via Boatanchors wrote:
> Rob:
>      What is the value of the cap and what did you pull it out of?
>      Here's why I ask. I've worked on a few BC-348s with .01 Micamolds and they were all bad and, I'm assuming, paper. However, I've worked on an R-45/ARR-7 where the caps were .0082, not .01, and all were good. I'm wondering if the .0082 caps were actually mica.
>                          Joe Connor
>
>      On Monday, March 21, 2016 8:34 PM, Rob Atkinson <ranchorobbo at gmail.com> wrote:
>   
>   
>
>   I am certain I have read or heard here and there over the years that
> "Micamold" branded caps, are fake micas, actually paper dielectric
> caps in a molded case made to look like genuine postage stamp micas.
>
> Well, tonight I took a bad one I had pulled out of a rig and busted it
> apart with a hammer, only to find what certainly appeared to be thin
> strips of mica layered on top of each other and sandwiched into metal
> grips, one on each end of the cap case and soldered to wire leads.
> So, I don't know how anyone got the idea that these are not real mica
> caps because the "micamold" that I broke apart certainly appeared to
> be the real deal.
>
> 73
>
> Rob
> K5UJ
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