Caps are Consistently Low Tol

Among the stuff that I scrounged a week or two ago I got bag of a
hundred capacitors. I think they're ceramic, and I'll describe the
case. It's black and 5 mm square by 2mm thick, and is labeled

CK05
BX
821K

on one side and

200V
A V X
7322

on the other side. I assumed that they were 820 pF, so I measured a
dozen of them with the AADE LC meter IIB. I got a consistently low
reading, somewhere in the 730 pF plus or minus 30 pF. These caps would
be old, maybe more than 30 years old judging by the date code. But I
would think that ceramics shouldn't change that much over the years.
Were they just not making caps right back then?

I checked for them using Google, and got this:
http://www.mouser.com/index.cfm?&handler=data.listcategory&D=80-CK05BX82
1K&terms=80-CK05BX821K&Ntt=*80CK05BX821K*&Dk=1&N=0&crc=true

Says it's 10%. So the minimum they should be is 738 pF. But most of
the dozen I checked were at or below this, so they are mostly out of
tolerance.

Eh?


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changed it: http://physics.nist.gov/cuu/Units/binary.html
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reading, somewhere in the 730 pF plus or minus 30 pF. These caps would

Buy a brand new one. Verify your meter is giving sane results.

 

Oh yeah, maybe I should'vc mentioned that. I have a bag of 470 pF 1%
silver mica caps, and when I measure those with the meter, they measure,
for example, 468.8 pF, 471.8 pF, 467.5 pF, and two in parallel measure
940.3 pF. So yes, I verify the accuracy of the meter on occasion. And
I'd say that it's fairly accurate.

 

Here's the actual data sheet:
http://www.avxcorp.com/docs/Catalogs/ck05-06.pdf

There was a big uproar about faulty 'mil-spec' resistors some years
ago..

Best regards,
Spehro Pefhany

 

Yeah, everything's the same except for the A V X is now changed to a
more complex code.

One would think that if these came in a bag, like they were NOS, new old
stock, they would be reasonably within tolerance. Might be that the
distrib was picking out the good ones and selling the rest to those of
us less perceptive with the hope that they wouldn't get any of them
returned as defective. Oh, well.

http://www.speff.com

 

A lot of the stuff floating around on the surplus market are
factory rejects. Usual corporate policy is to sell such parts
unlabeled or scrub the labels, especially on mil-spec parts,
but this doesn't always happen.

Where exactly did you scrounge them from?

Tim.

 

The Powers That Be decided that the college didn't need an electronics
program anymore, so they closed it down this summer. They gave the
rooms to another dept, and they just set all the contents of the drawers
(and even some of the drawers) out in the middle of the sidewalk for the
custodians to toss in the trash bin. I came along and scrounged what I
could manage to carry. I got a couple pounds of resistors, still im
bags, too. I'll have to check some of those to see if they're ok. I
got three hundred SGS-ATES 2N3055E power transistors still in the
styrofoam packaging paterial, probably worth a hundred or so. A couple
hundred sockets for the 2N3055s. A Cornell Dubilier capacitor
substitution box from a long, long time ago. A couple two-way radio PTT
microphones. A couple hundre 1000 uF 50V capacitors, Sprague, I
believe, but they're old timers and are at least five times the volume
of the more modern ones found in SMPSes. Anyway, I haven't had time to
look thru all the stuff to find out what I got. Maybe I'll sell some of
the stuff on Ebay.

 

Depending on the age, some of the older capacitance meters applied a
DC voltage during the test and it might change the reading a little.
You could put a bigger cap in series (X100 or more) with one lead and
apply a DC voltage through a 1 meg resistor to see if it changes
anything. The old Sprague TO-6 I had was adjustable up to 600 VDC.