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Author Topic: Mystery Capacitor Type  (Read 1288 times)
AC5UP
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« on: November 11, 2012, 10:56:40 AM »

Thought sure I could ID these little dudes on the web but no luck so far...

Visualize a 1/4 watt metal film resistor. Axial leads, nothing remarkable, except the color bands are Brown-Black-Black-Gold-Black and my DMM says it's wide open. Cap checker says 10 pf on the nosie. Body color is a pale yellow (slime) green and I also have them in a pink body color. Color code reads just like a resistor. Brown-Black-Red-Silver-Silver is 1,000 pf, Brown-Black-Orange-Black-Gray is 10,000 pf. The tolerance / voltage bands are a little different, but aside from that what I read on the first three bands agrees with my cap checker.

Tried scraping the paint from one to see if it had a glass body, but it's epoxy coated with a very scrape-resistant epoxy. No obvious marking for polarity so I don't suspect Tantalum. Therefore, the question is......... Are these ceramic or what? The 10,000 pf jobbies in particular are a mystery to me as that's .01 uf and they're profoundly small for the value.

If it helps, I'm tearing down reels of parts tape that came out of Rockwell-Collins in Garland, TX maybe 25 years ago. One of the reels has a label with "Rockwell" as the customer so these caps could be semi-exotic Buck Rogers kinda' stuff. They made Avionics & Satellite goods at that site and the resistors are so tight I could plotz. I tested a lot of 20+ 1k 5% metal film resistors that look exactly like what you'd find in consumer goods and all were within 10 Ohms........   Shocked

So....... Has anyone ever worked with caps like this? If so, what are they, what's the intended application, and what's a good assumption for the voltage rating?

BTW:  Also found some odd green tantalum bead caps that measured a dead short on the DMM. Magnifying glass showed markings of " LF 3/8A ". I'm assuming that's a 375 mil LittleFuse.

I love this stuff..........   Grin
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WX7G
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« Reply #1 on: November 11, 2012, 11:51:19 AM »

The capacitors are most likely ceramic dielectric with the 10 pF having an NPO temperature coefficient and the 10,000 pF having a X7R temperature coefficient. Given the size the voltage rating of the 10 pF might be 100 or 200 volts and the 10,000 pF might be 25 volts.
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WB6BYU
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« Reply #2 on: November 11, 2012, 12:02:48 PM »

I inherited a bunch of parts from my Dad, mostly dating I think from the late 1940s, including
several bundles of such capacitors.  The ones I've used appear to be ceramic as far as
I can tell.  I did open one up - accidentally, of course, apparently due to too much current
through it - but don't remember the detail of the innards.  I think the common term was
"tubular ceramic" capacitors.

Disk ceramic caps are available in sizes up to 0.1uf, so I don't see why 10nf would be a
problem for such a capacitor.

My older Allied's Radio Data Handbook (1943) doesn't show them, but the newer fifth
edition (1969) does, along with a note that all such tubular capacitors are rated at
500 volts.  (Often there will be a wide band at the beginning that indicates the
temperature coefficient, followed by the standard bands for value and tolerance.

These are basically axial-lead variants of the more common radial-lead tubular capacitors
as far as I can tell, though there were paper capacitors made in a similar style.

You might find more information by looking up MIL-STD-20D or EIA standard RS-198.


At least that might get you started in the right direction.
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N4NYY
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« Reply #3 on: November 11, 2012, 12:49:14 PM »

Can't believe you did not throw them out last month.
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AC5UP
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« Reply #4 on: November 11, 2012, 01:51:29 PM »

Funny you should mention that.........

I have a box of part tapes that I managed to misplace a while back and just recently found in the garage. I have been thinning out the junque collection and thought maybe I'd thrown them away 'cuz there really can be too much of a good thing. Parts tape is a cheap way to build a junque box but also requires time to strip out the parts, sort and organize them, then discover you now have 2,000+ resistors with only 16 different values. Let's just say that if I live to be 120 y/o I will never run out of 1k 5% 1/4 watt metal film resistors. Or .001uf 50 volt ceramic bead caps. Or 1N4454 switching diodes.

Did some parts sorting today and one of the reels gave me a pantload of 1N4003's which was pretty cool. I also found a reel with the HP 1N5711 Shottky diodes I admire so much. Some folks claim that's the absolute best choice for a detector circuit and much too good for a Philco while others say nothing is too good for a Philco. I say you'd have to be a doof to restore a Philco. In any case, I refreshed the 1N5711 stash today...

Note to WB6BYU:  Yup, I know what the older tubular ceramic caps look like. They were somewhat rare back in the day but these are similar only in concept. Tiny little bastids, you'd mistake them for a 1/4 watt film resistor if you didn't notice the fifth band. I know SMT tantalum's can run that much capacitance in a similar package size but they're always marked for polarity. For all I know the tolerance band end of these is 'assumed' negative, but ceramic makes more sense than tantalum...  ( ? )
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AC5UP
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« Reply #5 on: November 11, 2012, 03:42:35 PM »

HOT DAMN I found a picture!

The contributor who uploaded the pic to Wiccanpedia claims it's a ceramic.  So now we know.

Slap me upside the head and start calling me Vinnie.................   Tongue
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N4NYY
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« Reply #6 on: November 11, 2012, 04:23:58 PM »

HOT DAMN I found a picture!

The contributor who uploaded the pic to Wiccanpedia claims it's a ceramic.  So now we know.

Slap me upside the head and start calling me Vinnie.................   Tongue

I would have never guess them as ceramics.
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AC5UP
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« Reply #7 on: November 11, 2012, 05:55:13 PM »

http://static.happyplace.com/assets/images/2011/09/4e775803ceb14.jpg

BTW:  Even the blind carpenter who picked up his hammer and saw can tell you the answer is five.... That's how you square a form.   Grin
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WB6BYU
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« Reply #8 on: November 12, 2012, 06:46:50 AM »

I got a bunch of 0.5pf capacitors in packages like that - rather smaller than I would
normally use in HF circuits, but they make great stand-off insulators for ugly construction
where I don't want to use a 1M resistor.
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KB3HG
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« Reply #9 on: November 12, 2012, 08:37:24 AM »

5UP,

Watch those remarks about carpenters. Smiley

Kb3hg
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