. A system of multiplex telephony by the use of vacuum tubes . relay-ing action is possible both at audio and radio fre-ouencies. 22 Generator Circuits Ho^ such a tube may be used in a generativecircuit will now be tal<-cn up. Pis. 10 shows a tubecircuit in which a source of alternating currentmakes the grid positive and negative, ihe platecurrent will follow the sine variation, but neverreverses in polarity; from S of transformer T, areal alternating- current may be drawn. The t-nergyat S comes from battery B, while that used in the?rid circuit conies from the alternator. If part ofthe ene
. A system of multiplex telephony by the use of vacuum tubes . relay-ing action is possible both at audio and radio fre-ouencies. 22 Generator Circuits Ho^ such a tube may be used in a generativecircuit will now be tal<-cn up. Pis. 10 shows a tubecircuit in which a source of alternating currentmakes the grid positive and negative, ihe platecurrent will follow the sine variation, but neverreverses in polarity; from S of transformer T, areal alternating- current may be drawn. The t-nergyat S comes from battery B, while that used in the?rid circuit conies from the alternator. If part ofthe energy at S could be turned back into the ?ridcircuit and could be thus employed to do the excit-ing, it is evident the system would be self excit-ed and would constitute an oscillating circuit. Itis necessary that the energy turned back for excit-ing purposes have the correct amplitude and phaserelation with regard to the plate current. The fre-quency depends UDon the value of the inductanceand capacity of the circuit. Fig. II shows such anoscillatory 23 The indijctances L and Lt form the coupling be-tween the Dlate and ?rid circuits, by means ofwhich part of the energy is transfered back to thegridas excitation energy. The frequency of the un-damped oscillations persisting in circuit 0,L isdetermined by the values of capacity G and induct-ance L according to the eouation N = ., cycles T^QT second. The resistance H may be usedto control the amplitude of the andto determine ^he rate at which the oscillationsbuild up or die down. L is the coupled inductancefrom which energy may be drawn to an external cir-cuit for use. The action of this self-excited generator system; is illustrated in fi?. 12. The curve is that of one of the YT-2 tubes used in this work. Below the curve is the - time curve for the increasing grid voltage, and on the ri^-ht-hand side is shown the current-time curve. The dotted line is the average value of the current. It is now evide
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