GB793422A - Improvements in or relating to multi-stage high-frequency amplifiers - Google Patents

Abstract

793,422. Valve or transistor amplifying circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. June 25, 1956 [June 28, 1955], No. 19611/56. Classes 40 (5) and 40 (6). In a tuned multi-stage amplifier in which the impedances of two or more valves or transistors vary to a different extent when a bias is varied, the circuit impedances are proportioned in inverse ratio to the degree of variation of the valve or transistor impedance to which they are connected. As applied to a frequencymodulation receiver in which successive stages 7, 12 are biased from the grid currents in grid circuit resistors 8, 16 respectively, so that the later stage 12 handles the larger signal and so produces the biggest change in input capacity when the signal level changes, the L/C ratio of the tuned circuit 14 feeding the later stage 12 is made correspondingly smaller than that for the earlier stage 7. The L/C ratios of the primary circuits of the band-pass filters may also be chosen in a similar ratio. As an alternative to adjusting the L/C ratios the valves may be connected to suitable tapping points on the circuits.