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Farnsworth Multipactor Purchased!!!

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  • Farnsworth Multipactor Purchased!!!

    So this gem popped up on ebay a couple weeks ago. First listed for $1000, no bids, then listed for $400, no bids.... I contacted the seller, and guess who it was, Philo's grand daughter! Her father just died and she's been helping her mother sell the last of his stuff. She was happy to take $200

    Updates will follow once it arrives.

  • #2

    I thought I would post images of that multipactor.
    Attached Files



    • #3
      Thanks vidbib.

      Looking through the patents, it appears this is a radial version of the scheme embodied in figure 6 of this patent US2071516A:

      Also similar to figures 5-8 in US2143262, but without the split cathodes:

      Any speculation is welcome.

      I'm hoping to find out from Eric Dollard at some point if he ever played with this exact tube, since it was in Philo's son's collection, and he may have come in contact with it.

      USPS estimates delivery Monday!
      Last edited by SuperCaviTationIstic; 07-06-2018, 06:15 PM.


      • #4
        It has arrived!

        So there is a heater filament in the very center. This is surrounded by the high voltage anode wire screen. Outside that is the secondary anode wire screen, and finally the cathode on the outside, made of some type of thin foil....silver?

        Filament is just under an ohm cold.

        There's a getter that's been burnt up connected to the cathode which looks normal.

        The cathode has evidence of heat discoloration towards the bottom and the foil is peeling up a tiny bit here and there. On some of the cathode supports there is evidence of partial melting, but it's not destroyed.

        The secondary anode adjacent to the cathode has a couple segments of wire blown away near the bottom, which have stuck to the glass envelope.

        Looks like maybe there was arcing between anode and cathode.

        The supports for the elements have shifted off axis slightly. I don't know how critical this is to operation. Nothing is shorted out and the filament isn't burnt out so hopefully it still functions to some extent.
        Attached Files