Anode effect: The influence of electron bombardment of the anode on flicker noise

Experiments are presented which indicate the existence of two types of flicker noise in vacuum tubes with oxide-coated cathodes. The first is "normal" flicker noise that is present for anode voltages below 10 volts; the second is the "bombardment-enhanced" flicker noise that is added when the anode voltage is above 10 volts. It seems that the latter can be attributed to the arrival of neutral oxygen on the cathode. Since most pentodes and triodes operate with anode voltages above 10 volts, the "bombardment-enbanced" flicker noise should be a rather common source of flicker noise in these tubes.