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

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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

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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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18 THE 1GXATIAS experimenter tli ‘ tremendous possibilities tlmt were eon-neeted with it. In 190( Dr. Lee deForest was allowed a patent for a detector of electro-magnetic waves employing two electrodes in an open flame. One year later diligent endeavor on the part of this same gentleman had brought forth the real three electrode Vacuum Tube. Jt is well to understand at the outset that the vacuum bulb in this form was intended as a wireless detector but was subsequently found to function in a multitude of different ways. Some of the most important variations of actions will form the main body of this treatise. The major service performed by the tube is in wireless. It functions as a detector, an amplifier and an oscillation generator. The first two terms are self explanatory and by an “oscillation generator” is meant the tube when so acting that it generates radio waves of continuous amplitude and frequency. It is this last application that has made the radio phone so perfect and has caused the displacement of the old fashioned spark set in transmission of telegraphy and the substution of the new bulb Continuous Wave transmitter which is less costly, more silent, and possesses an efficiency that the old spark transmitters could in no way equal. We can attribute the rapid development of this device to nothing else but the fact that its applications are so numerous and so diverse and to its efficient action under varying conditions. It is truly an exemplification of tin fabled “Genic in a bottle.” The war added impetus to investigations that were already under way. There was a crying need for such a device and scientists of all nations delved deep into the subject of Thermionics. Important discoveries were made both in America and in Kuropc but on account of the absence of intercommunication no scientific data could be exchanged or no mutual hell) secured. However the result has becu so gratifying as to satisfy even the wildest hopes. The study is still