Positive-Grid Characteristics of a Triode

By operating the grid of a triode at a positive potential it becomes a virtual cathode discharging electrons with uniform initial velocity, and thus a recent theory by Jaffé becomes applicable. The positive-grid characteristics of a number of radio receiving tubes are determined and matched with those determined from theory. Agreement, satisfactory under given conditions, is found in the region of low plate voltages. Departure of the experimental curves from the theoretical ones is discussed. Practical tubes tested do not, by any means, correspond to the ideal conditions of the theory: the electrodes are not plane; the electrostatic field is not homogeneous; secondary emission from the grid is present; contact potentials exist; and there is always a velocity distribution among the electrons. Nevertheless, the investigation points a way toward a better theory of the triode.