GB309187A - Improvements in and relating to thermionic or like amplifying systems - Google Patents

Abstract

309,187. British Thomson-Houston Co., Ltd., (Assignees of Bradbury, B.). April 7, 1928, [Convention date]. Thermionic amplifiers.-In order to secure a high degree of amplification that is substantially uniform over a wide range of frequencies, the aperiodic output circuit of a high-impedance screened grid amplifier 1 is transformer-coupled to the tuned input 10 of a succeeding valve, the coupling-transformer 9 having a one-to-one ratio, or having a greater number of turns in the primary than in the secondary so as to secure a high plate-circuit impedance. The primary and secondary windings are closely coupled, one being wound over the other so that the adjacent ends of both windings are at the same potential with respect to ground. The windings are separated by such an extent that the combined capacity and magnetic coupling gives a substantially uniform voltage amplification over the whole frequency range to which the set is tunable. Preferably the primary and secondary are wound in opposite directions so that the capacity coupling is in opposite phase with the magnetic coupling. As shown the screened grid amplifier 1 feeds a detector valve 2 back-coupled through a circuit comprising a variable choke and followed by two low-frequency stages 3, 4. The various circuits may be separated by grounded screens. A variable resistance 22 in the filament circuit serves to control volume.