Capacitors

Discussion in 'Homebrew and Kit Projects' started by KE0M, Aug 20, 2008.

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  1. KE0M

    KE0M Ham Member QRZ Page

    Hi, I recently got a little package of assorted ceramic disc capacitors from radioshack and I need NP0 ceramic type capacitors but I can't tell if any of these caps are NP0 types. Is there anyway to tell?

    Thanks,
    KE0M
     
  2. KL7AJ

    KL7AJ Ham Member QRZ Page

    If they're "old school" capacitors, they will say NPO right on them. I'm guessing if this is a grab bag, there aren't any in there. Alas, NPO capacitors are getting to be as rare as hen's teeth. Check with the official QRZ parts exchange, though. I'm sure someone has a few.


    Eric
     
  3. KL7AJ

    KL7AJ Ham Member QRZ Page

    Check this guy out, too


    http://www.leaven.com/ti/tinpo.htm
     
  4. K5UOS

    K5UOS Ham Member QRZ Page

    NPO caps

    Joe,

    Some of my old NPO have a black tip painted on top. I don't use any of my old stock anymore due to the availability of better quality. I don't trust some of the old stock I have or the stuff I get from Radio Shack.

    Check the Mouser catalog. They sell NPO capacitors under COG or NPO.
    Prices are good and the quality in my experience is great. I use the epoxy coated and the ceramic COG/NPO in both tube and solid state.

    I have been specifically using the KEMET epoxy coated caps offered by Mouser in a very tough vacuum tube environment for a few projects. The are small grain sized caps and are very stable even in this high temperature application.

    http://www.mouser.com/

    GL Joe

    73 K5UOS
     
  5. KL7AJ

    KL7AJ Ham Member QRZ Page


    UOS....this is good news indeed. Thanks for the tip. For a while there, we were in a real quandary. I don't know why the old NPOs became so rare. I was having to relearn how to custom compensate my oscillator circuits due to the dearth of NPOs! (Not that it's a bad skill to learn anyway. :) )

    Eric
     
  6. AI3V

    AI3V Ham Member QRZ Page

    A fella could measure the capacitance, and put a little heat to the cap and see what happens.....

    http://www.interfacebus.com/Design_Capacitors.html

    I suspect you will find the unmarked caps to be a pretty temperature sensitive material, But you might be pleasantly surprised.

    Rege
     
  7. KL7AJ

    KL7AJ Ham Member QRZ Page


    When it comes to thermal stability, I've NEVER been pleasantly surprised in all my born days of hamming!

    Nice thought, though. :)

    eric
     
  8. AC0FP

    AC0FP Ham Member QRZ Page

    Look at the color dot on top of the capacitor

    Lots of good advice so far. I have purchased some of the Radio Shack grab bag capacitor assortments in the distance past. The ceramic disk capacitors are generally marked NPO or they may use the "skull cap" color dot system. A black dot indicates NPO and an orange dot indicates N150, blue = N470, violet = N750 etc... Thats all my memory will do. The color code is the standard resistor color sequence with each increasing color indicating a more negative temperature coefficient. If there is no mark other than the value code, i.e. 103 = 10,000 pF then the caps TC is probably X5F or Z5U etc...

    73,

    Frank:)
     
    Last edited: Aug 20, 2008
  9. K8ERV

    K8ERV QRZ Member QRZ Page

    What values do you need? I can check my stock, never tell what's in there. Maybe Vanna.

    TOM K8ERV Montrose Colo
     
  10. KE0M

    KE0M Ham Member QRZ Page

    Thanks to everyone for their help. In the radioshack bag there are some caps with black dots on top but there is only one that will be of use to me. The values I need are 47, 270, .1, .22, 33, and 200 pf. If you had any of those that would be great.

    Thanks,
    KE0M
     
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