Another mystery variable capacitor

Discussion in '"Boat Anchor" & Classic Equipment' started by W7UUU, May 10, 2018.

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  1. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    Here's another sort of odd (to me) variable capacitor I came across recently. I've seen these before over the years and seem to recall they relate to boatanchor receivers of the past.

    It's quite long - 10 inches. There are four sections, with three of them about 75 pF and the small one about 50 pF. Lots of lovely silver plating, as would be expected.

    Does anyone recognize this? None of the markings say much of anything useful other than what appears to be a part number of P-719687-1 but most likely a house number.

    My main curiosity is the length: was this intended to extend through a chassis, and provide ganged tuning to four separate sections, with each capacitor inside a shielded compartment? That's my guess, and where my vague memory of seeing this in an old receiver (Hammarlund is what sticks in my memory).

    But knowing the great brain trust here, I'm betting this will be identified quickly. What to do with it? Well, that will be determined at some point :)


    DSC_0078.JPG DSC_0081.JPG
  2. KG5QBI

    KG5QBI Subscriber QRZ Page

    I think it is very similar to the cap used in the Hammarlund HQ-140-x that I have never seen in person, but see this video below at 37:13. However this one uses a 3 gang capacitor, not the 4 gang you have, and the Hammarlund, or at least the one pictured appears to have brass plates, so this may be a different manufacturer, but similar concept. But it does confirm that at least one use is as you surmised.

    W7UUU likes this.
  3. W7UUU

    W7UUU QRZ Lifetime Member #133 Volunteer Moderator Life Member Platinum Subscriber QRZ Page

    Thanks for that - interesting video (long!)

    And yes, it's certainly the same idea - much of what I had figured. But not the same.... compare the capture below to the photos I posted. Similar for sure


  4. K1ZJH

    K1ZJH Ham Member QRZ Page

    Looks military.

  5. N2EY

    N2EY Premium Subscriber QRZ Page

    I don't know what it's from.

    But it appears to be from a receiver with 2 RF stages. I say this because the three sections are the same value, but the fourth section is a smaller value. This would make sense if the sections were (left to right in the picture) tuned circuit at first RF amplifier grid, tuned circuit between first RF amplifier plate and second RF amplifier grid, tuned circuit between second RF amplifier plate and mixer grid, and local oscillator.

    73 de Jim, N2EY
    W7UUU likes this.
  6. K8ERV

    K8ERV Ham Member QRZ Page

    Geeze, I ain't never seen nothing like that.

    TOM K8ERV Montrose Colo
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    I think it's a P-719687-1.:)
  8. KG5QBI

    KG5QBI Subscriber QRZ Page

  9. KG5QBI

    KG5QBI Subscriber QRZ Page

    I'm increasingly thinking this design was used in some form of aircraft radio at some point in time.
  10. KM1H

    KM1H Ham Member QRZ Page

    Why? Aircraft radios are typically shrunken versions of bench type radios.
    Here is a Hammarlund SP-600 version but I have no idea why yours is so long with just 4 lonely gangs.



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