University of San Francisco - USF Don Yearbook (San Francisco, CA)

Page 18 text:

The Three Element Vacuum Tube Edward Slater, ’23 D EKING the last few years such amazing steps have been made in tin science of thermionios that the student, is compelled to make more than usual endeavors to keep abreast of developments. In no branch has the progress been more phenomenal than in the perfection of the three element Vacuum Tube. This particular device is fully worthy ill importance, as regards all other material advancement, to be classed with the automobile, the steam engine, the dynamo, the aeroplane, or the telegraph. In the blaze of our own accomplishments we are prone to forget that it was through the efforts of such men as Hertz, the scientist and electrician, Richardson, who formulated the electron theory, Maxwell and a score of others that this ago of ours has been one of exceptional mechanical triumph. The three element Vacuum Tube consists of an evacuated glass container in which is a filament capable of being heated by the passage of an electric current. This constitutes the first element and is sometimes and more correctly styled the Cathode. The second element is known as the plate or Anode and consists of a metal plate on one or both sides of the filament or else a metal cylinder completely encircling it. The Grid is the name applied to the third element, so called because it is usually formed of a fine grid-like wire mesh interposed between the anode and the cathode with a purpose to control and vary the flow of electrons from one to the other. In the year 1886 a scientist. Geitel by name, discovered that a heated filament in a glass container would charge electrically a metal plate placed in proximity to it. The

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SOLVED BY RADIO 15 The feelings of those present towards Luxor were now anything but favorable. They had caught only individual words, “chickens.” “rabbits,” “dawg,” but they could easily supply the rest. “Cotched,” Ah! that was really bad; “Cotched agin;” amazement at his wickedness spread over their faces; “cotched a third time.” Alas! from early years he was surely headed for perdition. “An now Ah leabs de inncrcence ob ma childhood—“spoke the radio Luxor brazenly. But it seemed as if other forces were entering to prevent the cleaning of Luxor’s breast. “Ila! Ha! Ha! I’ve got the goods on you this time, Luxor,” shouted the wireless, “that bill you---” The scandalized machine stopped, but all had recognized the voice. It was the sheriff’s. Euclid fainted, women shrieked, pandemonium reigned. The crowd shrank from Luxor and he disappeared into the night. Epsom in a moment was at the side of Euclid. Her eyes, on opening, would gaze up into his. She would read his yearning there and murmur “yes.” She would ever think of the radio as her savior, and would never know that Luxor had never dreamed of clearing his breast through it, but that a clever impersonator bribed by Epsom, had—well—we allow the veil of charity to draw its sheltering folds around Epsom ’s conscience.

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THREE ELEMENT VACITM TIRE 17 charge acquired in this ease was positive. Further experimentation proved that on increasing the heat of the filament the charge on the plate became less strongly positive and an evacuation of the container caused the plate to assume a negative charge. Edison noted that if a metal plate was mounted in an incandescent lamp a current would How between the plate and the filament if the plate was connected to the positive side of the filament but not if the same was transposed to the negative. This action has been known as the “Edison Effect.” In 1888 J. J. Thompson proved that electrons carried the current that flowed across the space between the filament and the plate and later Richardson explained this How and postulated that the particles in matter, even though solid, were in movement as are the particles in a gas, that these were restrained in their proper positions ordinarily but under influence of heat, etc., it is possible for particles or electrons to break from their parent nuclei, force their way through others of their kind, overcome surface tension and shoot out into space. The first scientist to apply these principles and discoveries was l)r. J. A. Fleming who by means of a device which he called an “Oscillation Valve” was able to detect electromagnetic fluctuations in a current. This “Oscillation Valve” was composed of a metal filament surrounded by a nickel plate in an exhausted glass globe. As a detector of electro-magnetic waves it was not a great success but because of the fact that in such a device the How of current is unidirectional. it finds wide application as a rectifier for both low and high alternating current voltages. The Tungar and Kenotron rectifiers sold on the market today have as an essential constituent a valve manufactured on the same lines as the original “Fleming Oscillation Valve.” Mention has been made of this particular piece of apparatus because it was the first great step that started others experimenting along the same lines by offering something tangible with which to begin their studies. It brought forcibly to the