Patent GB-399033-A (GB)
Title: Improvements in and relating to the control of gaseous electron discharge tubes
IPC: H01J17/04
Filed: 1932-11-07
Abstract: 399,033. Rectifying alternating current. STANSBURY, C. and BROWN, G. C., N. 12th Street, Milwaukee, Wisconsin, U.S.A. Nov. 7, 1932, No. 31391. Convention date, Nov. 7, 1931. Addition to 375,031. [Class 38 (ii).] Relates to an arrangement for controlling the flow of current through a gaseous discharge valve supplied from an A.C. circuit and consists in applying to the control grid a potential which comprises a periodic transient potential obtained by the discharge of a condenser superimposed on an alternating potential of the same frequency as the supply so that a relatively small change in the control produces a large change in the current flowing through the valve. During the negative half cycle of anode potential of the valve 10, Fig. 1, a potential (e<r>, Fig. 2) consisting of the vector sum of the potential e<t> across the secondary winding 17 of transformer 15 and the potential e<1> between the points 3, 5 is applied to the condenser 6 and charging current flows via the auxiliary anode 13 and cathode. 11, the condenser potential e<c> during charge being approximately equal to and opposite to e<r>. When the applied voltage passes its maximum value current flow in the auxiliary anode circuit ceases and the condenser 6 commences to discharge through the resistance 7 giving a transient potential which departs from a sinusoidal form after a time t depending upon the value of the resistance 7. The potential between the grid and cathode is the vector sum of this periodic transient potential e<c> and the potential e<1> between the points 3, 5 and is shown as eg. By varying the resistance 7 eg can be varied between the limits eg<1> and eg2. For values of eg near eg<1> the grid potential becomes rapidly negative sufficiently soon to prevent the valve conducting current at the beginning of the positive half cycle of anode potential e<a>, so that no current flow takes place. When, however, the grid potential approaches eg<2> a point is reached where the grid voltage is not below the critical ignition voltage of the valve and conduction commences and continues throughout the whole of the half cycle. Thus by varying the grid potential between eg<1> and eg<2> the rectifier is transferred from the condition of complete blocking to that of full conduction ; eg can be varied by adjusting the value of resistance 5a or the condenser 4. In a modification the transformer 15 is omitted and the condenser 6 is charged periodically by grid current. The resistance 7 may be a photoelectric cell. In a further modification, Fig. 5, a transformer 45 having two secondaries replaces the transformers 1, 15 of the Fig. 1 arrangement. During the negative half-cycle of anode potential a current flows through the auxiliary anode 44 and the resistances 50, 51, 52 to charge the condenser 48. This condenser discharges through the resistances 49, 50 to give a periodic transient potential, part of which is tapped off by means of a potential divider formed by resistances 51, 52 so that a potential is applied to the grid which consists of an A.C. component due to the secondary winding 47 superimposed upon a transient potential, the magnitude of which is determined by the relative values of the resistances 51, 52. Thus by varying the resistance of 52, which may be a photoelectric cell, control of the valve is obtained. Thus, if the illumination of the photoelectric cell is above a certain value, full conduction of the valve is obtained, and if it is below that value the valve remains non-conducting.