Thoughts on using old mica capacitors

Discussion in 'Homebrew and Kit Projects' started by K8AI, Jun 5, 2017.

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  1. K8AI

    K8AI Subscriber QRZ Page

    I'd like to use some of those old "postage stamp" mica caps in some filter projects for HF with power levels around 100W. Any reason this should not be done? Yes, I'd rather use some high voltage silver mica or ceramics but I have quite a few of these old micas. Thanks.
     
  2. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Well, at this late date many have gone out of tolerance or have high leakage. Also, one can't tell by shape whether they are actually mica caps. "Micamold" is one brand that weren't even mica, but paper caps.

    -Verify the type by marks and brand
    -Test for value, leakage and ESR (if important for your application).
     
  3. KB4QAA

    KB4QAA XML Subscriber QRZ Page

  4. WB4WHJ

    WB4WHJ Subscriber QRZ Page

    I agree. I have used them a few times in recent past. Good service & no problems at all.
     
  5. K9STH

    K9STH Ham Member QRZ Page

    I would be very careful! If the capacitors are silver-mica, then there is a good chance that they may be leaky or even shorted.

    Use a good capacitor checker (one that puts several hundred volts on the capacitor being tested) to make sure that they are still good.

    Considering that new capacitors are inexpensive, you might just want to forgo using the old capacitors.

    Glen, K9STH
     
    W7UUU likes this.
  6. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    For 'old timey look" it is possible to make mold of an old capacitor then using a new cap, embed it in resin and paint it. Glen has experience with molding parts and can elaborate. Supplies are available at bigger hobby stores.
     
    KA9UCN likes this.
  7. K8AI

    K8AI Subscriber QRZ Page

    Have you priced new silver mica caps lately? Over a buck each and I need quite a few of them. I have a big bag of the old mica caps (not silver mica, by the way) already.
     
  8. WA7PRC

    WA7PRC Ham Member QRZ Page

    I was going to make a better recommendation but, they cost MUCH more than a buck each.
     
  9. K9STH

    K9STH Ham Member QRZ Page

    AI:

    Are silver-mica capacitors really required?

    Glen, K9STH
     
  10. KA9JLM

    KA9JLM Ham Member QRZ Page

    These are why I never learned my ABCs

    upload_2017-6-5_18-32-40.png
     

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