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

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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

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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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THREE ELEMENT VACUUM TI RE If) very young and no one ean foretell just where the Vacuum Tube will next assume the star role. General Theory of the Three Element Vacuum Tube The basis of thermionic action is the Electron Theory as formulated by 0. W. Richardson. An electron is defined as “A natural unit of electricity,” or the amount of charge carried by an atom of any univalent substance. If an electron becomes detached from an atom, the electron, which possesses a negative charge, leaves the remaining part of the atom with a plus charge. This partial atom is known as a positive ion. In like manner if an electron is added to an uncharged atom it communicates to it a negative potential and the combination of the two is called a negative ion. In this branch of therm ionics the electron behaves as if it possessed mass and can be so treated; also we are to deal with electrons that possess motion, for a stationary electron would be of no concern in a device like the Vacuum Tube. “What causes the electron to loose itself from the matter from which it comes and what subsequently impels it to fly through space!” When an atom becomes heated the electrons which it contains begin to move with increasing rapidity in a manner that might roughly be compared to the currents started when water is being heated to the boiling point. If this heating is continued, as in water, to a certain stage the movement becomes so vigorous that a portion of the electrons break away from the atom like steam from the water. This results in the decomposition of the atom when it takes place in a solid but. of course, does not hold for the water analogy. Whenever an electron is in such motion it is accompanied by an electromagnetic field. In this an electron produces an effect identical with a current of electricity. Thus a charge moving with a certain velocity is equivalent to a current possessing a strength equal to the charge multiplied by the velocity. When a Vacuum Tube is employed in a circuit the latter consists of two parts namely the ordinary wire circuit and a