GB251701A - Improvements in or relating to three electrode valves - Google Patents

Abstract

251,701. Marconi's Wireless Telegraph Co., Ltd., and Gill, E. W. B. Feb. 7, 1925. Vacuum tubes.-Negative resistance effects in a grid circuit are obtained by a triode con structed so that the maximum plate current under any poten tials on grid and plate is always less than the maximum cathode emission under these conditions, and having its grid and anode maintained at positive potentials such that an increase of cathode emission beyond a critical value produces a disproportionate increase in the grid current, and a corresponding decrease in the plate current. As this critical point occurs at higher values of the cathode emission when the grid voltage is increased, if the emission is constant an increase of grid voltage produces a decrease of grid current over a certain range. A cylindrical plate electrode should have more than 2¢, say 3 to 5 times, the diameter of the grid. When the electrodes are flat, the distance between plate and grid should exceed that between grid and filament. If the plate potential is +8 volts, that of the grid may be +30 to 45 volts. If a tuned circuit 4, 5 is connected to the grid, and the potentials adjusted to obtain the negative resistance effect, oscillations of high or low frequency may be generated, independently of any reactive coupling between the plate and grid circuits. If the grid potential be kept constant and the plate potential varied, a range can be found in which the curve showing the relation of plate voltage to grid current has a very steep portion, giving high amplification. This can be used to produce oscillations by reaction, the oscillating circuit being in the grid lead.