Vacuum tube system

318,235. Victor Talking Machine Co., (Assignees of Lafferty, C. L.). Sept. 1, 1928, [Convention date]. Thermionic amplifiers. - The filament or cathode of one of the valves of a thermionic amplifier is heated from a circuit associated with the anode of a second valve, in such a way that the voltage across it does not increase with a rise in current in the said anode circuit. The output of a full-wave thermionic rectifier is fed to a potentiometer R, and the filament f of valve 12 is heated from tappings 14, 15 on R intermediate of the tappings supplying the anode p of valve 17, through leads 21, 22. The anode p of valve 12 is supplied from a tapping 16, while grid-bias potentials for valves 12, 17 are supplied from tappings 13, 18 'respectively. The filament f or cathode of valve 17 is heated from a secondary winding s of the transformer T feeding the rectifier. In the arrangement shown, a gramophone pick-up P feeds the valve 12 with speech-potentials through a volume-control potentiometer 10 and transformer T while the two valves are coupled by a transformer T , and a loudspeaker E is fed from an output transformer T .