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Caps are Consistently Low Tol

Discussion in 'Electronic Components' started by Watson A.Name - \Watt Sun, the Dark Remover\, Sep 17, 2004.

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  1. 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


    on one side and

    A V X

    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:

    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


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  2. 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.
  3. 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.
  4. Here's the actual data sheet:

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

    Best regards,
    Spehro Pefhany
  5. 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.
  6. Tim Shoppa

    Tim Shoppa Guest

    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?

  7. 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.
  8. 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.
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