GB347296A - Improvements relating to thermionic valve circuits - Google Patents

Abstract

347,296. Valve amplifying circuits. GREELEY, P. H., 2632, Garfield Street, Washington, U.S.A. Oct. 30, 1929, No. 33017. [Class 40 (v).] In a thermionic amplifier in which the grid circuit of one valve is in parallel with the anode impedance of the preceding valve hum is prevented by providing predetermined impedances between the plates of a pair of valves and the high tension source so that the plate circuit impedance of the first valve is as many times greater than the impedance of the following valve as the amplification factor of the valve. The arrangement also prevents the large plate current variations of the output valve from affecting the earlier valves. Fig. 1 shows valves T1, T2 having anode impedances L1, R3 and L2, R4 fed from a source E having an alternating component G. Fig. 4 shows the application to a high-frequency amplifier in which hum may be produced by the resistance of the choke L11. In this case a resistance R12 may be added to make the resistance of the plate circuit of T10 equal to the resistance of the plate circuit of T11 multiplied by the amplification factor of the valve. The invention is also applicable to transformer coupled valves, in which case the transformer in the output of the first valve has a primary winding of low impedance. The leads between the valves and the coupling elements, if long, are twisted together to prevent undesirable pick-up of relatively high-frequency currents which would otherwise produce a high-pitched whistle. Specification 326,859, [Class 40 (v), Wireless signalling &c.], is referred to.