. The thermionic vacuum tube and its applications . es of Ep can beexpressed by a set of curves similar to those shown in Fig. 74 shows such a set of characteristics. The ordinates repre-sent current to the plate and not necessarily the emission current,, total current from the filament. When the grid becomes posi-tive it takes current and so can distort the Ip, Eg curves. A setof grid current curves for various plate potentials is shown in For the higher plate potentials these curves show a is due to secondary electron emission from the grid by theimpact of el
. The thermionic vacuum tube and its applications . es of Ep can beexpressed by a set of curves similar to those shown in Fig. 74 shows such a set of characteristics. The ordinates repre-sent current to the plate and not necessarily the emission current,, total current from the filament. When the grid becomes posi-tive it takes current and so can distort the Ip, Eg curves. A setof grid current curves for various plate potentials is shown in For the higher plate potentials these curves show a is due to secondary electron emission from the grid by theimpact of electrons coming from the filament (see p. 47). At the Flower plate potentials the stray field given by — is smaller, and THE THERMIONIC AMPLIFIER 151 fewer electrons are attracted to the plate. The secondary electronemission is then also less marked, so that the Ig—Eg curve shows arapid increase of Ig with increasing Eg. So far it has not been possible to derive the equation of thewhole characteristic theoretically with sufficient accuracy. For. 100 150 Anode Volts Fig. 73. the operating range of the characteristic, when the tube functionsas an amplifier, the plate current can be expressed by the equation.^ I^^a{^ZE,+ ^Eg-{-e^ .... (3) where SJSp and llEg are the filament-plate and filament-grid1 H. J. VAN DER BiJL, Phys. Rev., Vol. 12, p. 180, 1918. 152 THERMIONIC VACUUM TUBE voltages. If, for example, an alternating e sin yt beimpressed on the grid circuit the equation takes the form: (4) Ij)=a[--^+Eg+e sin vt+^) .
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