GB553967A - Improvements in or relating to radio frequency circuit arrangements comprising amplifiers feeding into a common load, for example, a radiating antenna - Google Patents

Abstract

553,967. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd., and MADDOCK, A. J. Dec. 9, 1941, No. 15857. [Class 40 (v)] A plurality of valve amplifiers supplied by separate HT sources, connected in parallel to a common load circuit such as an aerial, and excited by a common oscillatory source, are provided with a resistance network associated with the several HT sources and so arranged that, should one of the HT sources fail, a prohibitive bias interrupts the oscillatory feed from the exciting source. The object is to prevent damage owing to the inoperative valve acting as a rectifier of oscillations fed to it from the operative valves through the load coupling. As shown in the Figure for two valves having separate HT supplies +A and +B, these terminals are connected through high resistances R<SP>1</SP>A, R<SP>1</SP>B, to opposite corners 2, 4 of a resistance bridge. The other corners 1, 3 of the bridge are respectively earthed and connected through a negative bias source to the grid of a valve V of the unit by which the amplifiers are fed with oscillatory current. With both HT supplies A, B at normal voltage, the terminals 2, 3, 4 are all at the same positive voltage above the earth point 1 and the valve V is operative. Should either source fail, the voltage at 3 falls, and the valve V assumes a prohibitive bias. The Specification describes the relative values of the bridge resistances for a more general case using m and n amplifiers of which m have their HT supplies connected to the corner 4 and n to the corner 2 of the bridge Fig. 3 (not shown).