GB493136A - Improvements in or relating to thermionic valve amplifiers - Google Patents

Abstract

493,136. Valve amplifying circuits. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE. March 1, 1937, No. 6093. Convention date, Feb. 28, 1936. Drawings to Specification. [Class 40 (v)] In a push-pull amplifier in which the grid bias remains constant and has a value such that the valves are working at the maximum permissible anode dissipation, the load impedance is so chosen that the valves are swung asymmetrically, i.e. the anode current variations resulting from a positive grid voltage half cycle are, at maximum swing, at least twice as large as those resulting from a negative half cycle. A suitable value is between ¢ and “ of the commonly accepted " optimum load " Ra= h.Eb<2>/Ao where h is a constant between À6 and À8, Eb is the steady anode voltage and Ao the maximum allowable anode dissipation. The grid bias source must be independent of the anode current and the impedance of the anode supply must be as low as possible. A pair of valves which give an output of 10 watts with a noise faction of 5 per cent when worked class A factor, give an output of 30 watts and the same noise factor when worked in accordance with the invention. Known methods. as described for example in Specification 407,542, are adopted for compensating for flow of grid current and the impedance of the driver valve must be less than the load impedance of the output stage.