GB302180A - Improvements in or relating to circuit arrangements suitable for use in signalling systems - Google Patents

Abstract

302,180. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Moulton, A. B.). Dec. 10, 1927, [Convention date]. Systems for transmitting music and the like. -Signals from a number of different sources 1, 2, 3 are combined in the output of a common amplifier 8 through a balanced-bridge arrangement which maintains each of the separate input channels independent of each other and so prevents interaction. As shown in Fig. 3, the secondaries of each of the three input transformers 1, 2, 3 are connected in series through mid-point tappings so that the primary windings are electrically symmetrical with respect to those mid-points. The lead to the filament in each case contains an impedance network N which, in the case of the first transformer, balances the " load " consisting of the grid and associated elements of the combining valve 8. As shown in Fig. 3<a>, the balanced bridge for the second input 2 consists of two arms containing the half-windings c and d, the third arm comprising the balanced-bridge a, b, N1 for the first input, and the fourth arm an impedance network N2. Subsequent inputs are similarly balanced. The combining valve 8 is shown as of the . screened-grid type, though an ordinary three electrode valve may be used in combination with known methods of neutralizing the capacity coupling between the input and output electrodes. Alternatively a, push-pull arrangement of screenedgrid amplifiers is used. In this case the balancing networks N may comprise a three-point impedance, balancing both the " line " capacity and also the capacity between " line " and ground circuits.