An anomalous flicker effect in tubes with oxide-coated cathodes

An anomalous flicker effect is observed in tubes with oxide-coated cathodes if the grid bias is near zero volts. The time constant deduced from the noise spectrum is of the order of 10^-2second. The magnitude of the noise increases strongly with increasing temperature. It is impossible to detect individual noise pulses. It is proposed that the noise is caused by individual positive ions emitted by the cathode and trapped in the space charge. The effect is similar to the anomalous flicker effect in tubes with tungsten cathodes; it differs in the time constant (10^-2second instead of 10^-4second) and in the magnitude of the ion pulses causing the effect (single ions or small numbers of ions instead of about 10⁴ions per pulse).