GB261110A - Improvements in or relating to means for supplying power to thermionic valves - Google Patents

Abstract

261,110. Wright, G. M. Aug. 15, 1025. Thermionic amplifiers.-The plate potential of thermionic valves is supplied from a power circuit or the like, in such a way that a change in the supply potential is compensated for by a change of opposite effect in the grid potential, thus maintaining the effective output of the valve independent of the supply current variations. In the transformer-coupled amplifier shown in Fig. 1, a resistance NP is connected across the supply mains M, and opposite ends N, Pare connected to the grid and plate circuits respectively of the valve V. The filament is connected to a point F on the resistance such that FP/FN is equal to the amplification factor of the valve. The plate current is thus unaffected by alteration in the supply voltage, and such alterations produce no effect on the output circuit O, O. For the resistance-coupled amplifier shown in Fig. 2, the negative end N of the resistance NP is connected to the filament, and the opposite end P to the plate through the coupling-resistance R, an intermediate point F being connected to the grid circuit. If a is the slope of the grid-volts platecurrent characteristic of the valve, the point F is chosen so that NP/NF is equal to Ra; any change in the supply voltage then results in no change of plate potential, and therefore no effect on the output circuit O, O. A battery may replace the coupling-condenser C. When plate current is supplied by a local generator, an extra brush on the commutator may provide the intermediate tapping, the resistance NP being omitted. Condensers may be shunted across the resistance sections, their reactances being in the same ratio as the resistances. The directcurrent plate supply may be derived by rectification from A.C. mains. The invention may be applied to the elimination of audible hum in wireless receivers due to supply ripple, and to valves employed in central telegraph offices to prevent direct current bridges from being thrown out of adjustment by changes in the supply voltages.