Grid blackout in vacuum tubes

Grid blackout, variously called Whippany effect, desensitization, or grid effect, is a phenomena characterized by residual negative grid charging following application of voltages causing grid current to flow. All types of vacuum tubes examined have been observed to exhibit grid blackout in considerable variation. The effect is believed to be caused by formation of an extremely thin layer of evaporated semi-conductor from the cathode which causes the actual grid surface potential to differ from the applied grid voltage. Blackout mechanism performs an operation on positive input pulses to give an anode waveform similar in some respects to that caused by cathode interface except blackout time constants are very much longer than observed with cathode interface. Detection of blackout in a tube can be accomplished in several ways. A method which gives quantitative data is presented allowing characterization of the blackout effect applicable to calculation of circuit degradation.