Giant Capacitor (May, 1945)

Something tells me you wouldn’t want those girls to be sitting on this thing when it’s in use unless you like your models extra-crispy style.

THIS GIANT CAPACITOR, a 200,000-volt air condenser with a capacity of 2,500 mmfd., is used as a phantom antenna for testing high-power transmitters. It has 12 hollow plates made of 16-gauge sheet steel and plated first with copper and then with nickel to improve conduction. Shields at the ends of each plate prevent dissipation of electricity. The supporting insulators were designed for a 400,000-volt dry flashover. Despite its 10′ height and 2,000-lb. weight, the unit can be moved easily on its casters or can be taken down completely or assembled in a single day. It was built by the Federal Telephone and Radio Corporation, and is used to test large transmitters at full load without radiating any signals.

2 comments
  1. Stannous says: September 6, 200612:03 am

    I tried to find a modern equivalent of this and found an interesting comparison here:
    http://users.tm.net/lap…

    It seems as though the 2,500 mmfd (micromicrofarads or today, picofarads) isn’t that big anymore. There’s a pic on that page showing 19 ceramic one of that capacity.
    I’m sending a link to this page to the author in hopes he will post here and explain better than I can.

  2. Thomas says: December 26, 20081:56 am

    The capacitance isn’t big. It’s small. It was small back then, too. A 2500 MMFD cap of normal working voltage (50 to 400 WVDC) will fit in the palm of your hand, and will be quite small, too, even back then. What makes that capacitor so huge is its voltage rating. The plates have to be spaced far apart due to voltage reasons (so that the voltage doesn’t jump across from one plate to the other). Increasing distance decreases capacity. To bring the capacity back up, more plates have to be added. Also, since sparks jump from sharp objects better than rounded ones, all surfaces must be rounded. More metal must be added to achieve this (round tubes). Also, due to the wattages handled, the metal must be thick. Radio transmitters of the commercial variety put out hundreds to thousands of watts. All of that energy moving back and forth through that metal would heat it up if it wasn’t thick enough.

Submit comment

You must be logged in to post a comment.