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#12
October 30th 07, 02:44 PM
posted to rec.radio.amateur.boatanchors
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Paper capacitor recap opinions?
"Richard Knoppow" wrote in message ... "COLIN LAMB" wrote in message ... And, Phil's website is as good and concise as it gets about replacing capacitors. See http://antiqueradio.org/recap.htm Even if you have been doing it for years, you will appreciate Phil's nice writing style and useful information. And, a big fat A for taking the time to help spread his wisdom, learned from years of experience. Even after years of repairing radios, we learn that we can do it better. A few years ago I was going to replace a paper cap in a 17 tube receiver. I do them one at a time. I clipped the old one out, got a phone call and dinner call and shut the soldering iron off and left. I was not able to return to the work for about a month. By then, I knew there was a capacitor out - but I had clipped the old leads off and it took me an hour of tracing and schematic reading before I could determine where the missing capacitor was. Now, I am more methodical and make notes before I clip the capacitor. A notebook and pencil are always nearby to document before I start work. Life has been much simpler since then. And, it really is a good idea to test the radio after a maximum number of changes. Colin K7FM I will add to what is on this page that the flat molded caps are often also mica types, however, they are not silvered micas. They are simply stacks of alternating mica dielectric and foil plates. They are not as reliable or high performance as silvered micas and should be checked. These were used mostly in high voltage applications or where waxed paper had too much loss. Black Beauty caps are not exactly paper dielectric but used paper impregnated with a polyester. They _should_ have been low loss and quite reliable but became notorious within a few years of their manufacture for developing high losses. I suspect this may have been due to some problem with the molded casing because Sprague sold capacotors with a similar construction but in dipped epoxy casing as Orange Drops and I have not heard that they shared the same short life problems. BTW, while silvered mica caps are generally very reliable they can still go bad. I've had to replace quite a few in rebuilding a couple of SP-600-JX's due to instability. Here again all were molded bakelite cases so I suspect either the case or perhaps end connections. Again, the dipped epoxy mica caps do not seem to suffer from this problem. -- --- Richard Knoppow Los Angeles, CA, USA I discovered that any of the flat "Domino" style caps with Micamold stamped on them are best replaced. Paul P. |
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