Back when I was replacing those bad caps in mil equipment they were known as TDBPC's (Those Damn Black Plastic Capacitors), yup they were/are a problem.
BTW I did add a very small amperage fuse in the BC-348R B+ line as protection against a shorted or leaky bypass/coupling cap.  Cheap insurance, but I forget the value, been a long time since I've been in there...
Tim
N6CC

On Wed, Mar 27, 2024 at 1:27 PM Richard Knoppow <1oldlens1@ix.netcom.com> wrote:
   These were paper caps in postage stamp packages like mica caps. I
can't find any technical data but they seem to have been used in place
of mica caps during WW-2 when mica was in short supply. I was warned
about them by my mentor when I was a kid. All I have ever found were
leaky. I think Solar made similar caps. Both Micamold and Solar made
other types of caps. The Micamold caps I've dissected have no obvious
mechanical faults but seem to have stopped being capacitors at some
point. The package is similar to a larger mica cap. There is a dot code
on them, cant remember but it marks paper or mica with a color dot.
    Curiously, both Micamold and Solar dissapeared at around the same
time, around 1947. Have never found out what happened to them.

On 3/27/2024 12:24 PM, hwhall--- via ARC5 wrote:
> But Micamold did make real mica capacitors, so the name alone isn't a
> red flag for replacement. Most of us know that but I bring it up for the
> benefit of possibly new restorers reading the thread.
>
> Wayne
> WB4OGM
>
> On Wednesday, March 27, 2024 at 01:21:16 PM MDT, Ken
> <kgordon2006@frontier.com> wrote:
>
>
> I recently rebuilt an NC-57 for a kid.
>
> Every single micamold cap in that radio were so leaky they were more
> like bad resistors than capacitors.
>
> I literally hate those things.
>
>   They certainly are not mica-anything: they are squashed poorly-made
> paper caps.
>
> Ken W7EKB
>
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--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998
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