Figuring out max capacitance for a salvaged variable cap?

Discussion in 'Wireless & RF Design' started by BlackCow, Nov 17, 2010.

  1. BlackCow

    Thread Starter Active Member

    May 11, 2009
    65
    1
    I don't have to be spot on, but what would be a good guesstimate of max capacitance for this variable capacitor? [see attached picture] I salvaged it out of a very old (non working) tube AM radio.

    I noticed there are two leads, so I'm thinking it might be two variable caps in one?

    I was thinking it might be around 400 pF max?
     
  2. debjit625

    Well-Known Member

    Apr 17, 2010
    790
    186
    Its Air Dielectric Gang Condenser (capacitor),these contains two or more sections the capacity of which can be changed from a single knob.The max capacity of each section is usually from 300 pf to 500 pf.

    Good Luck
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    It is a double variable capacitor.
    One has a large capacity (it has 9 plates in the stator).
    The other is much smaller (it has only 5 stator plates, that are even cut out in the middle).

    [​IMG]

    I added the picture with text for some explanation.

    Bertus
     
    Last edited: Nov 17, 2010
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  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Yes. One section tunes the antenna tank to select a station and the other tunes the local oscillator to beat with the station frequency and produce a 455 KHz difference for the IF stages.
     
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  5. BlackCow

    Thread Starter Active Member

    May 11, 2009
    65
    1
    Thanks, so is there an easy way to test to see what capacitance each bank has.

    My multimeter is very basic and doesn't have a capacitor check. It seems like I really should invest in a better one!

    Can anyone recommend a good meter that would do this and, if not asking too much, an inductance meter?
     
  6. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
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  7. Paulo540

    Member

    Nov 23, 2009
    188
    0
    Well, I've had this here craftsman 82139 for at least 5 years and it's actually been very reliable and accurate, for a 20 dollar meter. Doesn't do inductance but I have a frequency generator for that.
     
  8. KB9BVN

    New Member

    Nov 28, 2010
    1
    0
    Build this one:

    LC Meter Kit

    AADE makes a GREAT LC meter too, but it's more expensive.
     
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