GB781215A - Selective bridge amplifiers employing discharge tubes - Google Patents

Abstract

781,215. Discharge tube amplifiers. BENDIX AVIATION CORPORATION. April 29, 1955 [May 7, 1954], No. 12545/55. Class 40 (6). In a selective amplifier, a cathode follower feeds an impedance bridge, the output being applied to a differential amplifier. Input signals fed to cathode follower 1, Fig. 1, are applied from resistor R1 to an impedance bridge Zl ... Z4, the output from the bridge being fed from points 3, 4 to the grid and cathode of amplifying discharge tube 2. In a practical embodiment, Fig. 2, the impedance bridge Z1 comprises an inductor L2 and capacitor C2 in parallel with a further inductor L3 and capacitor C3, the remaining arms being resistors R3, R4 and R5. The circuits L2, C2 and L3, C3 are selected to resonate at the undesired frequencies so that the arm Z1 is resistive and little output is fed to tube 2. At the desired frequency the parallel combination L2, L3, C2, C3 will resonate as a parallel circuit and provide a high resistance so that a maximum signal is fed to tube 2. Further discrimination may be obtained by employing a series-tuned circuit between the resistor R1 and the bridge, Fig. 4 (not shown), the circuit being tuned to the desired frequency. This circuit introduces the minimum of attenuation at the desired frequency while attenuating the undesired frequency.