Glue Stick Variable Cap

Discussion in 'Homebrew and Kit Projects' started by KJ4IVD, Feb 29, 2012.

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  1. KJ4IVD

    KJ4IVD Ham Member QRZ Page

    The March 1 edition of Radio World Newspaper (trade paper for broadcasters) features a great 15-minute project: turning an empty glue stick into a variable capacitor, with a whopping range of 10-12 pf.

    Maybe not a terribly useful item, but for coming up with it, Frank Hertel (the engineer submitting the tip to RW) is "MacGyver" of the Week in my book.
  2. K8ERV

    K8ERV Ham Member QRZ Page

    Wonder what it's temco is?

    TOM K8ERV Montrose Colo
  3. K9STH

    K9STH Ham Member QRZ Page


    At VHF and UHF, the capacitance variation range is more than enough to tune the resonant frequency through a fairly large range.

    This capacitor might be a good candidate for a VHF or UHF receiver local oscillator or for a VFO that is multiplied several times to get to the desired frequency.

    Glen, K9STH
  4. VK2HHS

    VK2HHS Ham Member QRZ Page

    So simple it's genius.

    I'm sure the basic idea can be manipulated to drive a slug in and out of a close spaced winding on the outside of the tube to make an excellent component to be used in controlling a permeability tuned oscillator

    de VK2HHS
    Last edited: Mar 1, 2012
  5. WA9SVD

    WA9SVD Ham Member QRZ Page

    But as Tom implied above, if the temperature coefficient isn't stable or predictable (and I'd wager different brands and even batches of glue have different characteristics) it's purely an experimental design and would need some careful and rigorous testing before considering such a "device" in any frequency critical or frequency stable use.
  6. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    I maked a PTO with a mechanical pencil and a ferrite bead once. Worked really good too!
  7. KA9JLM

    KA9JLM Ham Member QRZ Page

    You can also twist two wires together and get the same result.

    It was called a Gimmick (in old school days), and was used for low PF cap needs.

    Stability depends on the type of wire used, and the Cap value is set by the number of twists and length of the wire.

    That is a interesting article. Thanks for sharing.
  8. 4L4AGU

    4L4AGU Ham Member QRZ Page

    Absolutely not new. We have done this with empty lipstick, at least 20 years ago.
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