How to read postage-stamp micas (not the color dots)

Kenneth D. Grimm, K4XL kgrimm at ADELPHIA.NET
Mon Feb 26 21:59:32 EST 2001

Mike Silva wrote:

> I've got some postage-stamp micas that have their values indicated via
> rather than color dots, and I don't know the code (except I can figure
> the mmf's).  Some examples:
> CM35E 103 JN3 (0.01 uf)
> CM30F 242 JP3 (2400 mmf)
> CM35F 103 GP3 (0.01 uf)
> It's the CM stuff and the JN/JP/GP stuff I don't know.  Checked some
> handbooks from 1950 to 1980 and didn't see anything.  Mostly I care
> the voltage ratings.  Thanks!

These three caps are marked according to Mil-C-5C standard of the
50s-60s.  The CM indicates "capacitor, mica."  The 35 simply designated
that it was mounted using leads.  I believe that the next number was the
voltage rating with E being 600volts and F being 1000volts.  Then the
capacitance, followed by the J for capacitance tolerance of 5% or G for
2% or K for 10% or F for 1%.  The next letter designated the operating
temperature range with M=-55C to +70C, N=-55C to +85C, O=-55C to+125C
and P=-55C to +150C.  The final number was either a 1 or a 3 indicating
a "vibration grade" of either 10 to 55cps or 10 to 2,000cps.  CC caps
were ceramic and CN were molded paper dielectric caps.  The numbering
systems were similar.  My memory is a bit fuzzy on some of the mil
numbering systems, but this is close if not exact.  Hope this is of
interest.  Perhaps it will inspire someone to check what I have
remembered and fill in the gaps.

Ken K4XL
k4xl at
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