Patent GB-547193-A (GB)
Title: Improvements in or relating to electron discharge devices and circuits therefor
IPC: H01J43/02
Filed: 1941-02-17
Abstract: 547,193. Thermionic valves and circuits therefor. ELECTRICAL RESEARCH PRODUCTS, Inc. Feb. 17, 1941, No. 2135. Convention date, March 2, 1940. [Classes 39 (i) and 40 (v)] A thermionic valve has cathode, control grid and anode, and a portion of the electron stream from the cathode passes, preferably through a hole in the anode, to a secondary-emissive auxiliary anode showing a dynatron characteristic By reason of the instability of part of this characteristic, appropriate circuit connections between the auxiliary anode and other elements of the valve such as the control grid enable the entire electron stream to be blocked or unblocked, while retaining full grid control in the unblocked condition. In the preferred form, shown in axial section in Fig. 2, part of the electron stream from cathode 17, through grid 18 to anode 19 passes through the aperture 30 in the anode and is deflected by the curved plate 20 through the collector grid 21 on to the secondary emissive plate 22. The grid 21 collects secondary electrons emitted by the plate 22 and is composed of vertical wires 35 welded to horizontal cross-bars at top and bottom. Alternatively the grid may be formed of horizontal wires welded to side posts 32, which also carry a shield 36. Further electrodes may be added between cathode and anode 19. The secondary-emissive material on the anode 22 may be a mixture of 75 per cent magnesium and 25 per cent barum, oxidized superficially. The characteristic of electrode 22 shows two positive potentials where the current is zero, the lower point being unstable. This is utilized in the basic circuit of Fig. 6, wherein anode 22 is connected through resistance R to grid-bias battery C which is such that the grid, which is tapped to a portion of resistance R, is biased to cut-off point when no current is flowing through this resistance. Deflector plate 20 is preferably connected to the cathode as shown, while collector grid 21 is taken directly to anode battery B. If the valve is initially non- conducting and a positive pulse is applied to R through condenser C, sufficient to raise anode 22 above the unstable potential and to permit grid 18 to pass a small current, the anode 22 will jump to the high stable potential and the bias of grid 18 will be carried up to the operating point. Similarly by momentarily lowering anode 22 below the unstable point its potential will fall to zero and the control grid 18 will revert to cutoff. In a modification, anode 22 may be connected to battery through a further resistance such that its potential is brought nearly to the unstable point, thus decreasing the value of the pulse necessary to operate it. The valve may replace gas-filled switch tubes in many circuits, such as a three stage ring counting circuit (Fig. 9, not shown) which is so arranged that the firing of any valve switches off the valve before and prepares the next valve to fire at the next pulse. All the valves may be mounted in the same envelope with a common cathode. In a generator of saw-tooth oscillations a condenser C10, Fig. 10, is connected between anode 19 and cathode. The charging of this condenser through resistance R, raises the potential of anode 19 to such a point that in spite of the blocked condition of the control grid a small current flows to the auxiliary anode 22 and switches on the tube, thus discharging the condenser and switching off. A condenser C20 between anode 22 and control grid 18 increases the speed of discharge. In a pulse inverting circuit, pulses are applied through condensers 70, 70<1>, Fig. 11, to a pair of valves D, E in parallel, the anodes being connected by a condenser C30 with the result that the firing of either tube will extinguish the other; each tube thus fires at alternate pulses. A multivibrator (Fig. 12, not shown), may be obtained by connecting the auxiliary anode and the control grid through a condenser. Instead of being connected to the cathode the deflector plate 20 may have control voltages applied to it (Fig. 13, not shown).