Patent GB-670636-A (GB)
Title: Improvements in electron discharge devices
IPC: H01J21/14
Filed: 1949-01-04
Abstract: 670,636. Electron discharge apparatus. ZENITH RADIO CORPORATION. Jan. 4, 1949 [Feb. 12, 1948; March 18, 1948; March 19, 1948], Nos. 205/49, 206/49 and 207/49. Class 39 (i). [Also in Group XL (c)] An electron beam is focused to pass through an apertured accelerating electrode and at rightangles to parallel conducting elements of an intensity control grid which is arranged at a distance from the accelerating electrode greater than at least one of the transverse dimensions in the aperture thereof. A limiter has a cathode 2, Fig. 1, concentrating member 3, accelerator 4, focusing rods 9, anode 5, control grid 6 and anode 8. The width of the aperture 7 in anode 5 is less than its distance from the grid 6. Alternatively, the apertured accelerator 12, Fig. 2, may carry a focusing flange 16; focusing rods or a slotted plate 17, connected to the cathode, may be provided. In another form, focusing flanges 16, 26, Fig. 4, may be provided on both sides of the first accelerator; a focusing member 17 ensures that the electron beam is normal to the control grid 13, and a second accelerating member 21, having a focusing flange 25, is followed by a focusing plate 22 and anode 23. The plate 11 and members 17, 22 may be connected internally to the cathode. A circuit arrangement, Fig. 5 (not shown), incorporating the limiter of Fig. 4, is shown by reference to curves, Fig. 6 (not shown), to produce an output signal of constant amplitude in accordance with an input signal. Further, by use of a load impedance which comprises respectively a tuned circuit, a resistance, or a capacity, the wave-form of the output signal may be made sinusoidal, squarewaved or triangular-waved. The tube of Fig. 4 is modified for use as a limiter and discriminator in a frequency-modulation receiver by the provision of cascaded control grids 13, 34, Fig. 7, which are shielded from each other by an extension on the focusing means 22. The output current modulated by the input frequency is explained with reference to curves (not shown) and to Fig. 10, wherein the first control grid 13 is connected through terminals 41, 42 to the I.F. amplifier and the tuned circuit 46 ensures that space current induces on the second control grid 34 an I.F. potential which lags by 90 degrees. A variation of the input frequency will produce a change in the voltage phase displacement of the two control grids with a consequent variation of output current to terminals 50, 51. The accelerators 12, 21 may be connected together internally or externally to positive potential 45 and the circuit capacity may be adequate without the need of a separate condenser 48. The electrode arrangement of Fig. 7 is mounted between mica discs, Fig. 12 (not shown), and have specified dimensions. Focusing variations may be compensated by a bulged control grid 61, Fig. 14; a transverse dimension of the aperture 15 is less than its distance from the bulged portion 61. Non- uniformity of the field and consequent variable mu effects are eliminated by providing a similar bulge in the anode 62. The tube shown in Fig. 7 may be modified by providing the second control grid 34 and anode with bulged central portions and by shortening the distance therebetween at the edges. The distance between the first and second control grids may be reduced over their central portions. An additional load impedance between the anode 23, Fig. 10, and output 50 is stated to improve the linear range of response to frequency variation.