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Show plow of Current in Vacuum Tube Electrons Move From Negative Nega-tive to Positive, Expert Explains. By RADCLIFFE PARKER In Radio World. The meaning of electric current has undergone a , change during the last 25 years. It was formerly assumed that something flowed in the conductor and that that .something moved fro"1 'lie positive to the negative nega-tive poles of a hattery or generator. Inside the battery or generator the flow was, of course, In the same direction but from the negative to the positive. Now an electric current Is known to be a stream of electrons moving In the wire or other conductor. conduc-tor. This stream does not move from positive to negative, but in the reverse re-verse direction. It would be logical to re-define the poles of a battery or generator gen-erator so that the electrons would move from positive to negative, but this change would necessitate a complete com-plete revision of electrical conventions. conven-tions. Now an electron is negatively barged; It would be necessary to call It positive. Any extensive change In conventions conven-tions would introduce . endless confusion con-fusion for a long time, and rather than to pay such a heavy price to correct a mistake It Is more convenient conven-ient to distinguish between an electric current and a stream of electrons. e still retain the old definition of an electric current and say that it I flows from positive to negative. Then we say that the electrons move in a stream in a direction opposite to that of the current, that is, they move against the current like a school of fish swimming upstream. Yet the electrons constitute all of the current. This way of looking at It does not necessitate changing any of the old conventions about current and accompanying accom-panying phenomena, and everybody, knows what is meant. Thus "current" Is purely a fictitious conception but It Is very convenient to talk and read about the fiction. The Filament Battery When a battery Is connected across the filament of a vacuum tube the current cur-rent flows through the filament In the direction shown by the arrows In Fig. 1, that is from the positive pole to the battery to the negative. Inside the buttery the current flows from negative nega-tive to positive to complete the circuit. , ; Around the heated or incandescent l portion of the conductor in the evacuated evacu-ated space there are many free electrons. elec-trons. These electrons shoot out from the filament to a certain distance and then return again. The hotter the filament, fila-ment, the more electrons shoot out from it and the farther they go before they return. No doubt as they shoot out and fall back they also drift toward to-ward the positive end of the filament under the Influence of the filament battery. That Is, they do a hop, skip and jump act from the negative to the positive ends. Now suppose that a plate battery be inserted in the circuit as shown in i W I UlililiH 1 0 FIG. 1 FIG 2 The filament current (left) flows from negative to positive inside the battery, but otherwise outside the battery. The same is true of the plate battery current (right). The circuit Is completed for the B current cur-rent through the vacuum in the tube, and this flow is known as the "space current." Fig. 2. The plale of the tube becomes positive pole, while the filament as whole Is a negative pole. The electrons elec-trons around the heated filament now come under the Influence of the plate. 1'hey are-attructed to It. Those which Venture too far nway from the filament fila-ment get caught by the plate nnd can-nt can-nt return. The higher the plate vltHge is the more the free electrons elec-trons attracted to the plate, lllllions cf them roach the plate every second, ihis stream of caught electrons con-Mliutes con-Mliutes the plate convection current, or (.imply the plate curt'ont. Tills current cur-rent Hows from the plate to the tila-Wont. tila-Wont. according to the old convention. Ihe at row s in Tig. 2 show the direction. direc-tion. How Current Divides. 1'art or the current goes down the Positive leg and part down the negative nega-tive leg of the filament. However, "null more of It goes down the nega-,lvp nega-,lvp leK ,i0 ( ti,,, f.u.t that :Ue volt-ace volt-ace between the negative leg and the Plfte Is greater than the volt ace be-tween be-tween the positive leg and the plate. H will he observed that that part of the current which Hows down the negative leg Is added to the filament current and that which tl ows down the positive leg is subtracted from it. i '"herefore, when the plate battery is '"rncd on the negative end of the tila-l'.:tnt tila-l'.:tnt gets' hotter than the positive C!d. It would seem that the average oI'ange in the filament temperature Should he nil. hut. actually, the effect f Hie application of the plate battery is to decrease the total effective filament fila-ment current iy an amount that will visually change the filament temperature. tempera-ture. There is very little difference between the cases where the negative of B Is connected to the positive A and where the negative of B is connected con-nected to the negative A. There Is never any alternating cur-, cur-, rent in the plate circuit of a vacuum j tube: the current is always In one direction, from the plate to the filament fila-ment inside the tube and from the" filament to the plate outside the tube. There may be an alternating component compo-nent of the plate current, which merely means that the direct current rises and falls at a certain rate, like the tides in the ocean. When one speaks of the alternating current in the plate circuit of a tube one means the variation varia-tion in the level of the direct current. Tills is known as pulsating or fluctuating fluc-tuating D.C. DC and A C Readings. For example, if the direct current In the plate varies regularly between 11 and 1 miliiamperes about the mean value of G miliiamperes. then the al- FIG. 3 FIG. 4 Diagram illustrating the flow of current cur-rent in the filament and plate circuits cir-cuits (left). In the vacuoui space the plate current flows from plate to filament. At right Is diagram Illustrating Il-lustrating the flow of grid current. When the grid is positive the current' cur-rent' flows from filament to grid In the external circuit and In the vacuous space it flows from the grid to the filament. ternating component of the plate current cur-rent has an amplitude of 5 miliiamperes miliiam-peres and its effective value when Its form Is regular Is about 3.5 miliiamperes. miliiam-peres. If the frequency of the variation in the direct plate current is large, say over 20 vibrations per second, then a direct current meter placed In the plate circuit would give an Indication of 6 miliiamperes, or the mean value of the varying plate current. If an alternating current meter is placed in the plate circuit the Indication will be about 7 miliiamperes. That is the heating effect of the entire fluctuating fluctu-ating but direct plate current. That would be the Important thing in choosing choos-ing transformer and loudspeaker conductors, con-ductors, because they would have to carry this current continuously without with-out undue heating of the insulation or of the wire itself. The important tiling from the point of view of drain on the "B" battery is the 6-milliampere direct current or mean value of the plate current. The Important thing from the point of view of output in the loudspeaker is the 5-milliampere 5-milliampere direct current. That alone is effective in producing a sound. Three-Plate Currents. Thus in the plate circuit of a tube we have to distinguish three different currents: First, the mean value of the fluctuating current, which determines deter-mines the rate of discharge of the "B" battery ; second, the root mean square of the total plate current; which determines de-termines the heating- of the load conductors; con-ductors; third, the alternating current component of the plate current, which determines the sound output power. But the plate current in a tube is never alternating as a whole. It always al-ways flows in the same direction. Under certain conditions there may also be a grid current flowing. Thii is exactly the same as the plate cur rent and Is produced in the same man ner. When the grid goes positive with respect to the filament, the grid becomes be-comes a miniature plate and it attracts electrons. This causes a grid current to flow from the filament to the grid outside the tube and in the reverse direction in the vacuous space. When the grid becomes very much positive it robs the plate of some of its electrons elec-trons and, consequently, the plate current cur-rent decreases while the grid current j increases. i |