GB576277A - Improvements in or relating to electron discharge valve amplifiers - Google Patents

Abstract

576,277. Valve amplifying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 20, 1944, No. 1092. Convention date, Jan. 20, 1943. [Class 40 (v)] In an amplifier for amplifying a wide band of frequencies, attenuation of high frequency signals, due to changes in the impedance of the input circuit as a function of the applied frequency, is compensated for by providing in the cathode circuit of the amplifier tube an impedance which is non-resonant within the said frequency band so as to provide negative feedback varying with frequency. As shown . in Fig. 1, the feedback path is provided by resistor 38 which has a very high value, substantially equal to the ratio of the impedance of the input circuit of valve 20 at low frequencies to the impedance at high frequencies, the time constant of resistor 38 and parallel condenser 40 being equal to that of resistor 16 and condenser 18. Since a high voltage is developed across the resistor 38, a portion of battery 36 is used so that the cathode of valve 30 is only slightly positive with respect to ground potential, thus providing correct grid bias. The input circuit includes a television pick-up tube 10. In a modification, an auxiliary valve may be used as the cathode resistor 38 (Fig. 2, not shown). In this case, the anode of a pentode is connected to the cathode of the valve 30 thus avoiding the use of a battery having a very high potential. A parallel adjustable resistor in series with a blocking condenser is provided to reduce the valve impedance to the desired value.