While a cathode emits more electrons than are required to supply the current demanded by other electrodes, it was generally accepted that the current cannot change appreciably with cathode temperature. Considerations of the current drawn by fixed electrode potentials, during change of cathode activation, have subsequently accepted a change in emitted electron energy spectrum as a cause of small current changes, since the change in potential depression in the virtual cathode cannot entirely compensate for the altered emission. Thus the present conception is of a smooth current variation with activation (temperature). The paper shows how standing waves in the virtual cathode tend to modify this simple model.A qualitative assessment of the possible effects of standing waves in the virtual cathode on the variations of current drawn leads to conclusions with which the experimental results are consistent. Time anomalies in the variations of current drawn under static conditions are revealed by experiment, and it is concluded that the major factor controlling the current characteristic is the standing wave pattern. It is postulated that changes of pattern are responsible for flicker effect.