A system of multiplex telephony by the use of vacuum tubes (1919) (14586568667)

Identifier: systemofmultiple00arno (find matches)

Title: A system of multiplex telephony by the use of vacuum tubes

Year: 1919 (1910s)

Authors: Arnold, E. H Throop, A. R

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Contributing Library: Paul V. Galvin Library, Illinois Institute of Technology

Digitizing Sponsor: CARLI: Consortium of Academic and Research Libraries in Illinois

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19 amperes and the plate voltage 30. If now the gridpotential is increased negatively, a point isreached where the plate current is entirely arr-ested. In other words, the grid now has a suffic-ient negative charge to repell all of the elect-rons emitted by the filament and hence none ispresent between grid and plate and therefore nocurrent can flow. The amplification constant for this tube maybe obtained from the curve. To produce a change of3 miilliamperes the change in plate voltage is from62 to 92, or 30 volts. To produce the same changeby grid potential requires a change from i volt to5.2 volts, a change of 4.7 volts. Then u = 30/4.7= 6.4. The power amplification must of course in-clude the current relations, and since the gridcurrent is very small, this constant approaches200. In Fig.9 we show similiar curves to the abovefor the VT_2, and again the specified values setdown by the designers give the best working curve,which approaches a straight line.

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20 The point on the ciir7e at which the tube isvised depcnts upon what perforniance is desired.Beferrin? to the VT_2 ^rid voltasre-plate currentcirve. If r)oint A of the curve is used, that is,a grid potential of -40 volts, a decrease negative-ly of this voltage causes a greater change in platecurrent than does an increase. Hence, if the tubeis used as a detector of radio frequencv oscilla-tions, and the grid potential is at A, the riseand fall o^ the incoming oscillations produces asirr.iliar rise and fall in the rlate current; butthe amplitudes of the increase i^ill be g-reater thanthe arr.plitudes of the decrease. Therefore a result-ant pulsating uni-directional current flows in theplate circuit and charges a receiver condenser ,which then discharges into the receivers once foreach group of received oscillations. If the tube is used in the resion of point B,there is no difference in the changes of platecurrent for an eaual decrease or increase of gridpotential. Therefore we may use

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1919

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