Improvements in and relating to electrical amplifiers, such as may be used for example in television

Abstract

Abstract 436,734. Valve amplifying - circuits. BLUMLEIN, A. D., 7, Courtfield Gardens, Ealing, and BROWNE, C. O., 29, Monks Drive, West Acton, both in London. April 17, 1934, No. 11602. [Class 40 (v)] An amplifier for handling a wide band of frequencies extending substantially to zero frequency, such as arise in a light-sensitive cell in a television system, the cell circuit is arranged to discriminate against high frequencies, and the amplifier circuit to discriminate against low frequencies, the several stages of the amplifier favouring different bands of the higher frequencies. In this way, battery noises and like low-frequency components are not unduly amplified. As shown, the resistance 3 connected in series with the cell 1 is of a high value, e.g. 5 megohms, so that the higher frequencies are shunted by the inherent capacities across the resistance and are not so effective on the grid of the valve 6 as are the lower frequencies. The valves 6, 11, 13, 14 are directly coupled to each other by potentiometers 7, 9, 12, the portions 7 being in the plate circuits of the valves. and the portions 12 in the grid circuits. The intervening portions 9 are shunted by condensers 10 of successively smaller values along the chain with the effect that successive stages favour successively higher bands of frequencies. Very low frequencies are not amplified in the valves 6, 11, 13, but only by the final stage or stages 14. The last intervalve coupling may include inductance coils 15, 16 which tend to intensify the discrimination in favour of the highest frequencies. Coils 8 may also be provided in the earlier stages in series with the condenser-shunted resistance 9. Parallel-resonant circuits tuned to a frequency higher than the frequency to be amplified may be connected across the anodecathode paths of the valves. The valves may have guard rings to prevent leakage between plate and grid ; and similar rings may be provided in the cell 1. In a modification, the high resistance 3 is shunted by a small capacity (À05 microfarad), and a low resistance (5000 ohms.) is connected in series with the combination.

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