Patent GB-693671-A (GB)
Title: Improvements in or relating to velocity modulation tubes
Inventor: LAMBERT DONOVAN ERNEST CHARLES
IPC: H01J25/08
Filed: 1951-08-16
Abstract: 693,671. Velocity-modulated tubes. STANDARD TELEPHONES & CABLES, Ltd. Aug. 16, 1951, No. 19348/51. Class 39(i) In a velocity-modulation tube in which an electron beam is projected transversely across a coaxial line resonator of a quarter wavelength and short circuited at one end, and including a probe antenna capacitatively coupled to the centre conductor of the resonator for coupling the device to an external circuit, the probe 26, Fig. 3, is mounted on a quartz or glass rod 29 secured transversely across an extension of the outer conductor 12 beyond the open end of the resonator. In assembly, the centre conductor 13 comprising two metal sheets secured to either side of two longitudinally separated metal spacers or, as shown, two metal sheets secured together at top and bottom, is secured to the outer conductor via metal shorting disc 23, and holes are accurately jig drilled in the outer conductor 12 to take vitreous rod 29. The resonator is then tuned to mid-band frequency by capacitative copper tuning screw 24. The electron gun and collector electrodes, Fig. 2 (not shown), are then mounted on mica washers to form with the resonator and glass base 5, Fig. 1, a sub assembly. The sub assembly is completed by mounting .probe unit 26 on support rod 29. The other sub-assembly is formed by glass envelope portions 2, 3 sealed on either side of copper disc 4, and metal end cap 6 which is beaded with glass and sealed to glass tube 3 using a jig so the cap-disc spacing is accurately determined. The resonator and electrode subassembly is then slid into envelope portions 2, 3 until member 27 engages the inside of cap 6 and outer conductor 12 engages copper disc 4. The members 12, 4; 27, 6 are subsequently soldered together by means of tin rings during the processing of the tube. Rod 28 can pivot on support 29 so as to take up any eccentricity in disposition of cap 6. The gun includes two control grids. The outer conductor 12 is turned from a solid copper block and the opposite sides thereof are chamfered at 17; fins 19 are brazed to the sides of the slots in the outer conductor. The ends of two of the fins 19 have lugs 21 which project from the resonator wall and serve as location stops for the insulators carrying the gun electrodes: In a modification, the end cap 6 is dispensed with and a second glass rod secured to resonator wall 12 is used to support the upper end of probe 26. In this case the rod 28 need not be pivotable about rod 29. The use of cap 6 is however preferred since the device can then be coupled to an external coaxial line, instead of to a waveguide as in Fig. 1. In the frequency modulation system of Fig. 1 the tube disc 4 is clamped between insulators 33, 34 to the wall of guide 30, and the built in antenna projects into the resonant chamber defined by tuning piston 31 and diaphragm 32. Locating holes (not shown) in the edge of disc 4 enable the tube to be correctly oriented with respect to focusing magnet 35. Adjustable metal slug 36 controls the output power and the system may be secured to a further guide (not shown) via flange 37. Variation of the resonator potential may provide electronic tuning or continuous variation of frequency and may supplement the mechanical tuning. Specifications 587,664 and 587,619 are referred to.