GB441626A - Improvements in vacuum tube amplifiers - Google Patents

Abstract

441,626. Valve amplifying circuits. STANDARD TELEPHONES & CABLES, Ltd., 63, Aldwych, London.-(Assignees of Ware, L. A. ; 61, North Arlington Street, East Orange, New Jersey, U.S.A.) July 23, 1934, No. 21484. Convention date, Dec. 21, 1933. [Class 40 (v)] A thermionic amplifier of the kind employing negative feed back between output and input for distortion correction, and in which the amplifier gain-frequency characteristic is variable with frequency to correct for line attenuation, is arranged so that the gain-frequency characteristic of the forwardly transmitting portion is similar to that of the amplifier including the feed-back circuit. The forwardly transmitting portion of the amplifier comprises three cascade-connected stages 21, 22, 23, the intervalve couplings 3, 4, 7, 8 being so designed that the coil resonance occurs at the top frequency of the working range. In order to provide equal reduction of distortion over the range, the negative feed-back path taken from point A of the output resistance bridge Ro, 17, 1, 2 to the point B of the input resistance bridge R1, 18, 19, 20 includes a network 13, 14, 15, 16 tuned to the frequency of maximum line attenuation; the feed-back network is thus such as to give the amplifier with feed-back the same gain-frequency characteristic as stages S1, S2, S3 alone. Surging in the amplifier is also prevented by this means since the phase-shift frequency characteristic passes through 180‹ at the upper frequency of the working range while the phase-shift of the feed-back network alone passes through zero in the opposite sense at or near this frequency. The desired phaseshift conditions are assisted by making the values of the grid leaks 5, 9, as low as possible and by adjustment of resistances 3, 7. The amplifier is suitable for a frequency range of 50 to 500 kc. and is applicable to television and multiplex carrier telephony.