[Milsurplus] BC348 out of storage

[hwhall@aol.com]

I worked over a BC-342 not long ago & most of the caps were paper except for RF & IF tuned circuits. Lots of 0.01's, yep. Had a little pile of pretty black domino caps by Micamold afterwards & still haven't thrown them away (LOL).

Wayne
WB4OGM

On Monday, August 4, 2025 at 12:42:23 PM MDT, Joe Connor via Milsurplus <milsurplus at mailman.qth.net> wrote: 

Yes, Micamold did make some reliable mica caps. I came across them when I worked on a Hallicrafters R-45/ARR-7. They're .0082 mfd and did not leak. The troublesome ones in the BC-348 are .01 mfd. 

                                Joe Connor

On Monday, August 4, 2025 at 02:36:01 PM EDT, hwhall--- via Milsurplus <milsurplus at mailman.qth.net> wrote: 

Micamold did make real mica capacitors. Pre-WWII Micamold made mica caps in sizes from pF to as large as 0.02 uF. They started making lots of paper caps during WWII because mica was considered a strategic mineral resource. Afterward the war, it was just an accepted & cheaper method. And Micamold wasn't the only manufacturer who put paper-insulated caps into what looked like tabular mica capacitor bodies.

The most likely to be paper seem to me to be the black bodied rectangular ones with beveled corners and/or edges. Small brown square-cornered ones seem most likely to be mica internally. Low picofarad values are also more likely to be real mica. Location in the schematic is also a tip; caps used in RF & IF tuned circuits are more likely mica, audio & bypass caps more likely to be paper.

The attached Micamold advertisement (1954) hints at shapes that can be used as clues, with the exception of one body shape that it shows was used for both mica & paper.

Wayne
WB4OGM