716,372. Cold-cathode tubes. M-O VALVE CO., Ltd., and DUTT, T. L. Dec. 14, 1951 [Dec. 21, 1950; June 14, 1951], Nos. 31192/50 and 14165/51. Class 39(1) [Also in Group XL(b)] A method of manufacturing a gas filled electric discharge device comprising a tubular glass envelope filled with gas and an electrode assembly including a pair of main electrodes disposed substantially coaxially inside the glass envelope includes the steps of disposing the electrode assembly in the glass envelope approximately in its desired final position, inserting the envelope into a waveguide of predetermined dimensions in association with an inductive element of predetermined dimensions disposed across the waveguide so that the electrode assembly together with the inductive element forms a low Q resonent system, adjusting at least one member forming part of the electrode assembly until said resonent system is resonent at a predetermined frequency and fixing the electrode assembly in the position reached by this adjustment. The discharge device, Fig. 1, comprises main electrodes 1 and 2 formed on the ends of brass rods 3 and 4 which are screwed through copper bushes 8 and 9 seated in copper members 6 and 7 sealed to the glass envelope 5. Nuts 12 and 13 screwed onto the rods 3 and 4 abut against metal plates 10 and 11 soldered respectively to the members 6 and 7. An externally threaded brass tube 14 is soldered to the member 6 and a brass member 15 provided with external threads and a flange 16 is soldered to the member 7. A copper member 17 is soldered to the plate 10 and has sealed to it a glass dome 18. A brass tube 19 is soldered to the plate 11 and has soldered to it a copper member 20 to which is sealed a glass dome 21. A priming electrode 22 is sealed through the dome 21 and is insulated from the rod 4 by a glass sheath 23. A discharge device as shown in Fig. 1 and a second similar device having no priming electrode 22, the tube 19, member 20 and dome 21 being replaced by a brass cap, are inserted into a length of waveguide [see Group XL(b)], each in association with a respective inductive iris, to form a T.R. switch. In manufacturing the device the members 6 and 7 are sealed respectively to two short glass tubes having equal diameters and the bushes 8 and 9 inserted in the respective tubes. The free ends of the glass tubes are then joined together to form the envelope 5. The tube 14 and the plate 10 are then soldered to the member 6, and the member 15 and plate 11 soldered to the member 7. The rods 3 and 4 are then screwed through the bushes 8 and 9 and held in position by the nuts 12 and 13. The part of the device thus far assembled is then inserted in a rectangular waveguide in association with an inductive iris, the arrangement being exactly the same as will be the case when the discharge device forms part of the T.R. switch. The spacing of the electrodes 1 and 2 is then adjusted until resonance with the iris occurs at the desired mean operating frequency of the T.R. switch, and the electrodes 1 and 2 are then fixed in their final positions by means of the nuts 12 and 13. The assembly is then removed from the waveguide and manufacture of the discharge device completed in the normal manner. The device may be filled with argon or with argon and water vapour, the pumping and filling being facilitated by a duct 25 provided through the rod 3. A modified discharge device, Fig. 4, comprises a main electrode 35 formed on the end of a rod 38 which is screwed into a metal bush 39 soldered inside one end of a metal tube 40 which fits closely inside the glass envelope 37. Inside the other end of the tube 40 is soldered a metal bush 41 in which is soldered a metal tube 42 which is sealed through the envelope 37. A metal rod 43 is soldered to the rod 38 and passes through the tube 42. The second main electrode 36 forms part of a metal block 44 which is soldered inside one end of a metal tube 45, in the other end of which is soldered a metal block 46 to which is soldered a metal rod 47 which passes through a metal tube 48 sealed through the envelope 37 and is soldered to the tube 48 at its outer end. The device is inserted into waveguide [see Group XL(b)] in association with an inductive iris to form an A.T.R. switch, and is supported in two tubular metal members soldered to opposite faces of the waveguide. The tubular members form the outer conductors of two coaxial lines whose inner conductors are respectively formed by the tubes 40 and 42 and the tube 45, rod 47 and tube 48. The length of the coaxial line is,made equal to one and a half times the mean operating wavelength of the A.T.R. switch and the tubes 40 and 45 are each made half a wavelength long to provide effective short circuits between the inner ends of the tubes 40 and 45 and the adjacent faces of the waveguide to prevent loss of energy from the waveguide. During manufacture, the discharge device is inserted in a waveguide in association with an inductive iris in the same way as will be the case when the device forms part of the A.T.R. switch. The spacing of the electrodes 35 and 36 is then adjusted by turning the rod 43 until resonance is obtained at the desired mean operating frequency of the A.T.R. switch, and the electrode 35 then fixed in its final position by soldering the rod 43 to the tube 42 at its outer end. The Second Provisional Specification describes also an alternative form of discharge device comprising two main electrodes of conical shape mounted on the bases of two circular cylindrical metal cups. One cup is mounted on two wires secured to two metal pins sealed through a pressed glass base of a tubular glass envelope, and an axial priming electrode may be provided in the form of a thin metal rod secured to a third pin. The second cup is secured to a wire sealed through the opposite end of the envelope. When used in a T.R. or A.T.R. switch, the device is mounted in a valve holder disposed on one side of the waveguide. In manufacturing the device the first cup is mounted on a glass base which is sealed to a length of glass tubing. The part of the device so far assembled is then inserted in a waveguide in association with an inductive iris and the second cup inserted in the open end of the glass tubing and moved forward until the correct spacing between the main electrodes is achieved, whereupon the open end of glass tubing is sealed around the wire connected to the second cup to secure the second main electrode in its final position.