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Thread: Conducting high voltage/low amp electricity through vacuum?

  1. #1 Conducting high voltage/low amp electricity through vacuum? 
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    What if an alternating current is transformed to so extremely high voltage and low amps that it is electrically conducted through vacuum itself? Would that make the vacuum respond to electromagnetic influences like any other electrical conductor?


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    Quote Originally Posted by Martin J Sallberg View Post
    What if an alternating current is transformed to so extremely high voltage and low amps that it is electrically conducted through vacuum itself? Would that make the vacuum respond to electromagnetic influences like any other electrical conductor?
    Early X-Ray machines utilized A.C., as you suggest, applied to opposite ends of a specialized high-vacuum tube called then a "Coolidge Tube", after the inventor. I had one; the name Coolidge was inscribed upon it. It was a glass sphere about 5 inches in diameter, having two glass tubes about 1 inch in diameter affixed to it diametrically opposite each other, such that overall, the length of the tube between these "ears" was about 14 inches. Within the globe could be seen electrodes which were separated by about 3 inches. One had a small cup-shaped end containing a coiled filament, which was heated by a low voltage applied to the outside end of this element, which protruded from the end of that ear. The other ear had a massive copper-colored rod within it, the inside end of which had about a 1-inch diameter metal head cut at a 45` angle, in the center of which was a hard, heat-resisting insert, presumably tungsten.

    The cup-shaped element was the cathode. The other was the anode. When the cathode's filament was adequately heated by low voltage, about 5 volts, to a near white-heat, and a very high A.C. voltage applied across the two "ears", or elements, streams of high-velocity electrons flowed across the "gap" between the elements, but only during the half-cycle of A.C. during which the Anode was positive, striking the insert and causing X-Rays to be emitted from it, which "sprayed" outward from the 45` angle, through the glass globe, and on to a Barium Platino-Cyanide screen, which fluoresced under the influence of the X-Ray stream. Objects placed in this stream interrupted the beam, causing an image on the screen. Thus the bones within hands, feet (especially!), could be viewed directly by observers.

    The device using this type of tube was in widespread use across the United States in shoe stores, from the late 1930s until about 1955. The link below shows a pic of one of the machines.

    Adrian X-ray Shoe Fitter - Rarely seen: Hidden Collections of the Mutter Museum - brought to you by Juncanoo

    Edit: The Shoe-Fitting fluoroscope machine used a large transformer which weighed about 90 lbs. to provide about 80,000 volts at about 5 milliamperes to the X-Ray tube. The machine operated on standard 120-Volt circuits. To contrast this, the average dental X-Ray uses about 90,000 volts @ 0.005 Amp. (similar amounts of power). The difference being, of course, the vastly higher exposure time, which was arbitrary, with the shoe machines. I believe my own feet (and body) were exposed to X-Rays thusly as a kid, at least 20 times, maybe more. I am now 70, have experienced no ill effects that I know of.

    Re-Edit: Guess who got our local shoe store's machine, when they were ordered to get rid of it? I was about 14 then.........


    Last edited by jocular; April 26th, 2013 at 12:49 AM.
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