. The thermionic vacuum tube and its applications . e resulting current in the plate circuit. There arevarious ways in which this can be done. The circuit arrangementof a method proposed by S. Ballantine ^ is shown in Fig. 101. The coils 1 and 2 are so connected that the currents n and 2*2flowing in the directions of the arrows tend to neutralize eachothers effect in the secondaiy of transformer T. If h and ^2be the inductance due to the coils 1 and 2, respectively, and Ri beso adjusted that the tone in the receiver is a minimum, then ilti=,€ Ballantine assumes that ?2 = —^ from which he
. The thermionic vacuum tube and its applications . e resulting current in the plate circuit. There arevarious ways in which this can be done. The circuit arrangementof a method proposed by S. Ballantine ^ is shown in Fig. 101. The coils 1 and 2 are so connected that the currents n and 2*2flowing in the directions of the arrows tend to neutralize eachothers effect in the secondaiy of transformer T. If h and ^2be the inductance due to the coils 1 and 2, respectively, and Ri beso adjusted that the tone in the receiver is a minimum, then ilti=,€ Ballantine assumes that ?2 = —^ from which he then obtains,1 S. Ballantine, Proc. , Vol. 7, p. 134, 1919. 200 THERMIONIC VACUUM TUBE since eg=iiRi, Rxtz (43) The assumption made is, strictly speaking, justifiable only whenthe impressed oscillations are very small, because the current-voltage characteristic of the circuit is not linear unless the externalimpedance in the plate circuit (, the impedance of coil 2) islarge. On the other hand, if it is large the current io cannot be. —II— h ^2 — = Ki- ^2 M (44) (44a) For a simplification of this dynamic method I am indebted toan hitherto unpublished suggestion of Mr. H. W. Everitt which is THE THERMIONIC AMPLIFIER 201 shown in Fig. 102.^ It consists in replacing the transformer T by-two non-inductive resistances ri and r2, the telephone receiverbeing connected directly to them as shown. The effect of the
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