: 4e449b27.6000...@mindspring.com Content-Type: text/plain;
charset=ISO-8859-1; format=flowed 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
-- Message: 3 Date: Fri, 12 Aug 2011 13:24:13 -0400
From: Garey Barrell k4...@mindspring.com To: drakelist
drakelist@zerobeat.net Subject: Re: [Drakelist] PTO capacitors.
Message-ID: 4e4561bd.5080...@mindspring.com Content-Type: text/plain;
charset=ISO-8859-1; format=flowed Ski - A little research shows that the
'Electro-Motive' (EM) corp was acquired by Cornell Dubilier (CDE) in 1978. It's
possible that CDE modified the manufacturing process, but I doubt it. I've used
these caps both professionally and amateur, and never found them to be
particularly failure prone. I was using them in the 60's for 400 MHz solid
state amplifiers built on stripline. We used an epoxy solvent to dissolve the
brown case, resulting in a capacitor consisting of a stack of silvered mica
pieces with a copper 'wrap' around the ends, that could be soldered directly to
striplines, an early form of surface mount! Obviously the idea was zero lead
inductance, and several manufacturers later offered 'special' caps that looked
just like ours for stripline use.. Actually, until a year or two ago, the
first time I saw a PTO failure caused by one, I hadn't seen any more than
random, very occasional defective Dur-Micas. I've found only a couple over the
last 50 years in any application aside from the PTO. The silver migration
problem is exacerbated by high voltages, and they are mostly used in resonant
circuits where they see MUCH lower voltages, so that may be part of the answer.
Still, the one in Steve's PTO is at least 40 years old, so that's not likely to
be a 'manufacturing defect'! :-) 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
-- Message: 4 Date: Fri, 12 Aug 2011 20:19:54 -0400
From: john joh...@nc.rr.com To: k4...@mindspring.com,Fred or Ski
wb8...@frontier.com Cc: drakelist drakelist@zerobeat.net Subject: Re:
[Drakelist] PTO capacitors. Message-ID:
6.2.1.2.2.20110812201925.037bb...@pop-server.nc.rr.com Content-Type:
text/plain; charset=us-ascii; format=flowed At 11:16 PM 8/11/2011, Garey
Barrell wrote: 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 Darn caps, can't even get 50 years out of 'em these days! :-) John K5MO
-- Message: 5 Date: Sat, 13 Aug 2011 05:19:56 -
From: Henry Foglesong hwfogles...@gmail.com To: drakelist@zerobeat.net
Subject: [Drakelist] Drake front panels Message-ID:
17E77F522F7C43ECBBAD5D1CD460D24D@hamshack Content-Type: text/plain;
charset=iso-8859-1 Has anyone had experience with replacement panels from
KF8MW, and if so, would you comment on their quality, please? --
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-- Message: 6 Date: Sat, 13 Aug 2011 09:17:39
-0400 (EDT) From: K9sqg k9...@aol.com To: hwfogles...@gmail.com,
drakelist@zerobeat.net Subject: Re: [Drakelist] Drake front panels Message-ID:
8ce27d282c2234e-20e8-56...@webmail-d169.sysops.aol.com Content-Type:
text/plain; charset=us-ascii My experiences have been 100% positive. Tony is
a nice guy that does great work. 73, Evan, K9SQG
