Photomultiplier output signal control system

In the present invention, the output of an oscillator for a chopper circuit is applied to a flipflop circuit, and one output of this circuit is applied to one or more dynodes of a photomultiplier to thereby control a photo-electron current emitted from a cathode of this photo-multiplier tube. The other inverted output of the flipflop is applied through a capacitor to an anode of this tube and the output of the anode is fed through a tuning circuit to an amplifier. The capacitance of this capacitor is so determined as to cancel part of the control signal fed to the dynodes from the flipflop circuit, arriving at the anode through interelectrode stray capacitances. Lowering of the signal-to-noise ratio of the tube can thus be eliminated without adversely affecting the operation of any circuit or device in this tube. (Ohno, Y.)