Patent GB-610283-A (GB)
Title: Improvements relating to thermionic amplifiers
IPC: H04J1/00
Filed: 1946-04-04
Abstract: 610,283. Two-way transmission. KOSACKI, J. S. April 4, 1946, No. 10454. [Class 40 (iv)] In a two-way repeater, the' connections of a common amplifier valve A with two external circuits D1, D2 are automatically reversed, when the direction of speech changes, by biassing potential applied to rectifiers G1, G2, H1, H2, by a trigger circuit III under the control of a discriminator circuit II which tests the difference of levels between the ends of an attenuator K in the output of the amplifier valve A. The external circuits D1, D2 may be sections of a long-distance two-wire telephone line, in which the attenuation may be reduced to zero by the amplifier without the production of singing, or one of them may be an instrument which functions alternately as a loud-speaker and a microphone. Speech currents pass from line D1 to line D2 through the amplifier A by way of the direct connections E1, E2, and in the reverse direction by way of the cross-connections F2, F1. The speech voltages are superimposed on D.C. voltages which exceed their amplitude, so that the metal-oxide rectifiers G1, G2, H1, H2 are conductive or non-conductive according to' the polarity of the biassing voltage applied to them through the wires S1, S2. When voice currents arrive from the line which has been the outgoing line, the signal level at the output end K2 of the attenuator K rises above that at the input end K1, the output of the amplifier M2 temporarily exceeds that of the amplifier M1, and the resultant of the opposed rectified voltages across the resistances Q1, Q2, which is applied to the grid of valve R, is negative or positive according as the existing connections are through the direct paths e1, e2 (corresponding to traffic from D1 to D2 through E1, A, E2, valve,R being conductive), or through the cross-paths f1, f2 (corresponding to traffic from D2 to D1 through F2, A, F1, valve S being conductive). Reversal of the direction of traffic consequently reverses the trigger circuit III, and the latter reversal changes the circuits I, II from direct connection to crossconnection or vice versa, by means of biassing voltages applied to the rectifiers over a control path which includes the wires S1, S2 and S3 in series, together with the intervening conductors. The biassing voltage is applied between the ends of the wires S1, S3 by a battery V together with a resistance V1 which is of such magnitude that when the trigger valve S becomes conductive the resultant voltage applied to the wires S1, S3 is reversed in sign. The connections of the amplifier.A are thus reversed, but the consequent reversal of the level-gradient. in attenuator K does not cause hunting because the connections in the discriminator II also have been reversed. To allow for the relatively low level of speech from that line which is the outgoing line for the time being, the potentiometers W1, W2 may be so adjusted that amplifier M2 is more sensitive than amplifier M1. In modifications: (1) rectifiers may be connected in shunt instead of or in addition to rectifiers being connected in series with the speech-current paths; (2) the control potential may be applied through wires S1, S2 to the centre tappings of. the line transformers C1, C2, or between the wire J and a wire similarly connecting the amplifier transformers B1, B2; (3) the repeater may be interposed in a line containing ordinary repeaters, to enhance their stability; (4) amplifiers may be inserted in the crossed connections F1, F2, so that the gain is greater from line D2 to line D1 than in the opposite direction.