GB448113A - Improvements in or relating to thermionic amplifiers - Google Patents

Abstract

448,113. Distributing music &c. KOLSTER-BRANDES, Ltd., and EARP, C. W., Cray Works, Sidcup, Kent. Nov. 30, 1934, No. 34408. [Class 40 (iv)] [See also Group XL] An amplifier for a wide band of frequencies received over a low impedance line, e.g. radiofrequency signals extending from 150 to 1500 kc. distributed by a line with interposed amplifiers, comprises a number of valves in parallel each with its input connected across one element of a series-resonant circuit, these circuits being tuned to frequencies chosen at regular intervals within the band. Similar connections may be made on the output sides of the valves to an outgoing line. The input line I has one side earthed and is closed by a coil L and resistance R. Across it are connected a number of series-resonant circuits, each comprising a coil G1 .... G8, and a condenser G9 ... G16. The grid-cathode circuits of the respective valves V1 ... V8, which may be pentode valves, are connected across the respective condensers, and include a common biassing-resistance R2 and shunt condenser C2. The whole frequency range is divided into sub-bands and each resonant circuit is tuned to the mean frequency of a sub-band, so that its impedance for that sub-band is low and is thus matched to the low impedance line. On the output side, the line O is bridged by a coil L1 and resistance R1, and in addition a number of series-resonant circuits comprising coils P1 ... P8 and condensers P9 ... P16 are connected across the line. The plate-cathode circuits of the valves are connected across the respective condensers. Further valves and associated resonant circuits may be added to cover further sub-bands. Particular ranges of frequency may be boosted and the amplifier given any desired overall frequency characteristic. Automatic volume control may be provided for any sub-band amplifier that is liable to receive exceptionally strong signals.