Ski -
Yes, those are the 'Dur-Mica' style caps made by 'Electro-Motive', and used by Drake. That some are
failing almost 50 years later isn't all that surprising. I haven't run into these failures until
just the last couple of years, so perhaps they're all ready to fail! :-)
CDE also makes them, and I think the 'Dur-Mica' tag belongs to them. But silver migration seems to
be a problem with many silver mica caps. Early 'postage stamp' types were the worst, and it was
blamed on poor sealing of the lead/package interface. But then the epoxy dipped type developed
similar problems, just some years later.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Fred or Ski wrote:
After working in communications for the State Police here in Michigan for 37
years, most of our equipment was from Motorola, and we have had several
problems with silver mica capacitors made by a company that marked there
components with 'EM'. If you find a circuit that is in suspect of causing a
problem, and there is silver mica caps with 'EM' installed, replace them. Many
of our Motorola Micor radios had freq shifting and intermittant drive which
caused erratic power output. These 'EM' caps apparently had a contamination
when they were made and some didn't go bad for several years. I would
certainly check for these parts in the PTO's that are operating intermittantly.
I hope this helps...
Good luck and 73,
Ski-WB8YXI
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