Discussion in 'General Technical Questions and Answers' started by K4LRH, Jan 10, 2019.

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  1. K4LRH

    K4LRH Ham Member QRZ Page


    This is what I have learned thus-far about FILM CAPACITORS.

    Am I 'on track' or do I need enlightenment ?

    Jack; K4LRH

    Attached Files:

    Last edited: Jan 10, 2019
  2. KE4OH

    KE4OH Ham Member QRZ Page

    Sounds correct. But to summarize, in the context of amateur radio, film caps are a superior replacement for wax/paper dielectric caps found in older amateur equipment. The lifespan of film caps is virtually unlimited if working voltage is not exceeded.

    In audiophile circles, there is great debate on the relative sonic merits of one dielectric over another and also film-and-foil vs. metalized foil construction in audio circuits. But those factors don't really apply to our decidedly lo-fi radio applications.
  3. K4LRH

    K4LRH Ham Member QRZ Page

    Thanks for replying. I'm attempting to learn more about metalized foil construction.

  4. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    An additional advantage of film capacitors in some situations such as higher voltages is that they are self healing in the event of a pinhole fault between layers.
  5. KP4SX

    KP4SX XML Subscriber QRZ Page

    I once drilled a hole through one of the modern 'yellowcaps'. The value changed a bit but the cap didn't fail or go leaky! I've also subjected various subjects to the rigorous BIC LIGHTER TEST. Modern caps are great compared to their predecessors.
    N0TZU likes this.
  6. KD2RDG

    KD2RDG Ham Member QRZ Page

    Seems like you are on track.

    When capacitor shopping I look for what the leads are made out of as well. Some are steel and some are plated copper. I prefer the latter because I think they are easier to solder.

    Polarity is a little controversial and there is some superstition out there that the metallized film caps have some polarity even if they don't say they do. Some think they print the label on one side to help orient you. Others claim to have tested this. Lots of opinions. Good luck with this one.

    You didn't mention tolerance, a big advantage of most metallized film caps over their ceramic counterparts. Sometimes people are willing to pay more to know that the nominal value is likely to match up more closely with the actual value. I don't own a meter that does capacitance, so this is important to me.
  7. K4LRH

    K4LRH Ham Member QRZ Page

    Great replies. What's the 'BIC LIGHTER TEST' ?
  8. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Mr. Carlson discusses capacitor types and their uses....

  9. KB4QAA

    KB4QAA XML Subscriber QRZ Page

    Mr. Carlson discusses film capacitor polarity in tube or high impedance circuits....

    Last edited: Jan 11, 2019
    W5INC and N0TZU like this.
  10. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    As I recall the “polarity” mark shows which is the outer conductive side of the roll. Possibly of interest in high voltage applications but with modern body coatings I’m not sure it matters anymore.

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