Patent GB-367616-A (GB)
Title: Improvements in or relating to two-path two-way telephone and like transmission systems
IPC: H04B3/06
Filed: 1931-04-09
Abstract: 367,616. Valve amplifying circuits. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.- (Assignees of Hogg, J. L. ; 18, Webster Place, East Orange, New Jersey, and Doba, S. ; 2038, East 24th Street, Brooklyn, New York, both in U.S.A.) April 9, 1931, No. 10526. Convention date, April 19, 1930. [Class 40 (v).] A two-way amplifier is adapted to diminish the gain of outgoing signals and to increase that of incoming signals when the outgoing amplitude exceeds an upper limit, and to reverse these effects when the outgoing amplitude falls below a lower limit. Outgoing voice-currents pass from the two-wire circuit 1, 2 to the outgoing circuit T through amplifiers 5, 7, 8 and a loss circuit 6 wherein the signal currents pass through the series-connected anode-cathode paths of the valves 9, 10, so that a negative charge on the grids of these valves diminishes the gain of outgoing voice-currents. Incoming voice-currents pass from incoming channel R to the two-wire circuit 1, 2, through step-up transformers 23, 24, step-down transformers 25, 26, amplifier 98, and a loss circuit 27 which contains as shunts the cathodeanode paths of the valves 28, 29, so that a negative charge on the grids of these valves increases the gain of incoming signals. The grids of all four valves 9, 10, 28, 29 are connected to the plate 35 of a condenser, so that the state of this condenser determines the gain. Before conversation begins, relays 48, 50 are in the released position as shown and condenser-plate 35 is insulated. As soon as valve 5 is influenced by speech, relay 48 is operated (through valves 57, 59, 61) and discharges any negative charge on condenser-plate 35, so as to establish a high gain for outgoing signals. When the strength of the amplified currents outgoing from valve 8 rises above a prescribed lower limit, relay 50 is operated through valves 8, 65, 66 and, by causing battery 64 to block the grid of valve 57, it releases relay 48 so as to insulate the condenser-plate 35. During normal speech, relay 48 remains de-energized, as shown, while relay 50 remains energized. If, however, the strength of the currents outgoing from valve 8 rises above a prescribed upper limit, a negative charge is supplied by valves 36 .. 39 to condenserplate 35 so as to reduce the gain of outgoing and increase that of incoming speech-currents. When the strength of the outgoing speechcurrents again falls below its prescribed upper limit, the charging of condenser-plate 35 ceases, but the relays 48, 50 remain in the resting and operated positions, respectively. When the outgoing speech currents cease after having been at normal strength, relay 50 releases, but if speech recommences after a brief interval the relay 48 remains at rest as shown, since the valve 57 is blocked by the charge on condenser 62. If during speech the outgoing signal strength falls permanently below the lower limit, relay 50 releases and thereafter relay 48 operates and discharges the condenser-plate 35 as soon as the charge on condenser 62 has leaked away.