GB690720A - Improvements in two-way loudspeaker telephone installations - Google Patents

Abstract

690,720. Two-way transmission; loudspeaking systems. TELEAMPLIPHONE. Sept. 6, 1951 [Sept. 6, 1950], No. 21086/51. Class 40 (iv). In a two-way loudspeaker system a valve 105 is connected in the feed-back path of a line amplifier valve 103 to control its gain in accordance with the presence or absence of speech currents in its effective direction. Speech currents tapped off at M, Fig. 1, are amplified in valve 106 and after rectification in 107 are applied as a cut-off bias to the valve 105 and to one of the valves 201 in the amplifier B appropriate to the reverse direction. Valves 202- 207 and 101 are connected to give a symmetrical arrangement. In the detailed circuit, Fig. 2, negative feed-back from the output transformer 1035 is applied from the anode 1051 of valve 105 to the grid 1056 of valve 103 and to the anode 1011 of valve 101. Modified feed-back circuits are described with reference to Figs. 3-5 (not shown), and a 2-wire-4-wire termination incorporating arrangements according to the invention is also described. An additional arrangement in which the valve 105 is connected in parallel with valve 103 and acts as a shunt across the input thereto is described with reference to Fig. 8 (not shown).