. A system of multiplex telephony by the use of vacuum tubes . 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 fo
. A system of multiplex telephony by the use of vacuum tubes . 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 evident why the oscillating plate current reaches a maximum for the continuous oscillations. Highfrequency currents. 24 generated in this manner are not pure sinusoidsbut contain higher harmonics. 25 PART 3 From the discussion given on the operation ofvacT3um tubes as high frecuency generators, receiv-ers and amplifiers, it seems very nrohable thatthey may be used in these capacities in the devel-opement of a system of multiplex telephony. The first problem is to determine to what ex-tent speech frequency may be transmitted and receiv-ed thru these tubes without distortion, and to whatdegree, in a qualitative way, waves of this fre -quency are amplified. i^or the purpose of testing out and experiment-ing UDon such circuits as would be developed in thisinvestitration, a line of twisted pair No. 20 gaugewire was strung from the small Physics laboratoryat the north end of the main building of Armourinstitute to the room adjoining the instrument roomat the south end of the building. A double pole doub-le throw switch was connected at each en
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