# Capacitor question?



## acpeacemaker (Jun 11, 2011)

Hey, I was lookin' around for the silver mica capacitors on some stuff I had and cracked this open to find it wrapped in a gold strip. This came from some really old radio/8 track player. How odd is that for the the capacitor to have this?


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## Militoy (Jun 12, 2011)

Not unusual at all. That's a "dogbone" capacitor. Most of them are constructed with a combination of dielectric and conductive layers that are designed to compensate for temperature changes. They are very common in old RF circuits, and other circuits where the designers had trouble with temperature "drift". Though I've seen gold-colored conductors and film in some, I've never seen one with actual gold foil in it. But who knows? You might get lucky.

BTW - Dogbone capacitors can be good candidates for scrounging and reselling, if you find them in quantity. They are very popular with antique radio restorers - and in 35 years, I've never seen a bad one - unless it was broken in half like the one in your photo!


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## acpeacemaker (Jun 12, 2011)

Militoy said:


> Not unusual at all. That's a "dogbone" capacitor. Most of them are constructed with a combination of dielectric and conductive layers that are designed to compensate for temperature changes. They are very common in old RF circuits, and other circuits where the designers had trouble with temperature "drift". Though I've seen gold-colored conductors and film in some, I've never seen one with actual gold foil in it. But who knows? You might get lucky.
> 
> BTW - Dogbone capacitors can be good candidates for scrounging and reselling, if you find them in quantity. They are very popular with antique radio restorers - and in 35 years, I've never seen a bad one - unless it was broken in half like the one in your photo!


 Thanks for the answer Militoy. I went ahead and gave them their own bin to put them as I do with a lot of other ones. I couldn't help but, bust it open to see the goodies inside. It's nice to have little Christmas presents in June lol. -Andrew


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## Militoy (Jun 12, 2011)

acpeacemaker said:


> ...I couldn't help but, bust it open to see the goodies inside. It's nice to have little Christmas presents in June lol. -Andrew



I sure don't blame you for healthy curiosity! I make it a habit to de-cap, section, open, unencapsulate or x-ray every new type of componant I use. The inspections have saved me a ton of trouble and heartbreak over the years. Lately, with all the counterfeit parts coming out of China, AS9100 requires active monitoring for ersatz parts. The DPA (destructive physical analysis) is just a normal part of doing business.


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## Findm-Keepm (Jun 12, 2011)

I've been in the electronics business since the 70's and have never heard of them being called "dogbone" capacitors, ever. What you have is a dipped silver mica capacitor, in the CM05 MIL-spec series, probably made by either CDE or Sangamo. 

http://www.google.com/search?q=CM05...ct=mode&cd=2&ved=0CAgQ_AUoAQ&biw=1350&bih=602

There are quite a few postings here on the forum on silver mica caps and their yields. BTW, the FEDLOG/WEBFLIS entries for CM05 series caps make no mention of PM besides a few grains of silver, and no PMI (precious metal indicator) code. 

http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-C-5/mil5.pdf

I'd test that "gold" - you may find it to be simply a brass/copper or some other alloy. Keep in mid these caps have never commanded very high prices in low values such as yours. If it is indeed gold, you have a one-of-a-kind for sure.

Hope this helps,


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## Militoy (Jun 12, 2011)

Findm-Keepm said:


> I've been in the electronics business since the 70's and have never heard of them being called "dogbone" capacitors, ever....



"Dogbone" is a slang term used to describe rolled or stacked film caps of various types of dielectric construction - when they have the shape shown in the photo. I agree it's certainly not the term manufacturers use in their datasheets now days - they are obviously going to describe their product by dielectric type; ceramic, polyester or polypropylene film, mica, etc. Try a Google Image search under "dogbone capacitor".

You are correct about the low PMI on most caps. At least some metallized thin film caps do use evaporated gold film as the conductive deposit though. I don't personally process enough material to make caps worthwhile to consider - I'm an OEM manufacturer of aerospace equipment who primarily recycles his own scrap as a hobby. But some of the commercial processors on the forum process thousands of pounds of boards on a regular basis. I suspect since they are already processing tiny SMT ceramics for platinum, some may be running through-hole caps for silver and gold as well.


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## Findm-Keepm (Jun 13, 2011)

Militoy said:


> Findm-Keepm said:
> 
> 
> > I've been in the electronics business since the 70's and have never heard of them being called "dogbone" capacitors, ever....
> ...




Dogbone caps are ceramic caps, *not* silver mica or film:

http://www.surplussales.com/capacitors/RF-TempDogbone.html

What was posted was a picture of a silver mica capacitor, not a dogbone. The one google result for dogbone that shows a silver mica capacitor (blue background) is from some very misinformed eBay seller. 

Here's a very good image of what a dogbone cap is:

http://www.talonix.com/images/caps/CDC0122.jpg

There _are_ capacitors that utilize some gold plating (piston trimmers, some vacuum caps, and even some glass/"glassmike" caps from the 50's), but silver micas are not one of them. I've got buckets of silver micas - old and new, but absolutely zero gold in them, nor mention of gold in the datasheets or catalogs from the various manufacturers - Sangamo, CDE, Elmenco, and Saha. I have seen brass, tin and silver plated end crimps, and even a Murata capacitor series with solid silver end caps and leads (UY series), but sorry, no gold in silver mica caps like the one the OP posted. Gold passivated film caps are out there to feed the audiophile crowd, but even then, those things are very well marked as gold foil caps, with the various trade names. 

As for me, I'm a retired Navy avionics tech, and now 8 years along in the sourcing department for a passive electronics components distributor. 

Anyone else out there finding gold in capacitors??


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## acpeacemaker (Jun 13, 2011)

Well like I said, I was looking for silver micas. The "gold toned" part is a crimp that has a hole or slot the leg fits into. Ill test it here later....its going to be a busy day. In one month I've moved my family's things by myself from a house to storage to another house. (Enough to fill four car garages). Only to find out we moved right next door to a sex offender. (Child molestation by an older man) I have three babies under 7 so I don't feel easy. I understand these type of people are everywhere but damn my kids windows are 15 feet from his back porch. A lot of times I work at night 30 mins away so I can't stomach the idea of staying. Anyways, sorry my thoughts are coming out here but I guess it eventually had to somewhere. :|


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## acpeacemaker (Jun 13, 2011)

Just another pic of the crimp..


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## Findm-Keepm (Jun 13, 2011)

acpeacemaker said:


> I have three babies under 7 so I don't feel easy. I understand these type of people are everywhere but damn my kids windows are 15 feet from his back porch. A lot of times I work at night 30 mins away so I can't stomach the idea of staying. Anyways, sorry my thoughts are coming out here but I guess it eventually had to somewhere. :|



You have my deepest sympathies - we had a creep across the street who started sending letters to the neighbor's kid, only 7 years old. Fastest privacy fence I ever saw go up! One of my wife's friends retracted an offer on a house once she saw the sex offender registry for the neighborhood. It's like they move just far enough away from schools but close enough to be a burden on the rest of us. I've got a 4-yr old dauyghter, and she's never outta our sight.

One thing the neighbors learned - keep a log/diary of everything you notice - the cops and prosecutors need that to do their job. Also, enlist any of the other new (good!) neighbors to help keep an eye on things. It helps to leave an emergency cell number with them too - they can be your eyes when you aren't there. 

A surreptitious video surveillance camera or two aimed his way might also be of help - check the legality first.

Holding you in out thoughts and prayers!


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## acpeacemaker (Jun 13, 2011)

Thank you Findm, The good news is our new landlord has another house were getting at the first of the month. -plus its a lot closer to my work in a lot better neighborhood.


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