Patent GB-484004-A (GB)
Title: Improvements in electric vapour discharge tubes
IPC: H01J17/30
Filed: 1936-10-29
Abstract: 484,004. Metal - vapour apparatus. NOWAK, K. Oct. 29, 1936, No. 29431. [Class 39 (i)] [Also in Group XXXV] A discharge device comprises a solid cathode which is provided with separate heating means and is distanced or insulated from the auxiliary arc to a liquid cathode which is used for starting purposes. In one form, the arc between the indirectly-heated cathode 2, Fig. 1, and an anode 3 is started by an auxiliary arc formed, e.g. by tilting, between an anode 5, which is connected to the anode 3 through an impedance 6, and a mercury cathode 4. The heating current for the cathode may be switched on when the auxiliary arc is formed and may be reduced, e.g. when the auxiliary arc is extinguished, by means of an automatic switch actuated by a coil in the circuit of the main or auxiliary discharge. A glass or metal guard 11 screens the cathode 2 from the auxiliary arc and the electrodes are screened from mercury drips by a member 10. To protect the cathode from ionic bombardment, the main discharge circuit may be closed after the auxiliary discharge has been ignited. In another form, the mercury cathode 4, Fig. 2, and anode 5 are mounted in a separate vessel 7 which may surround, or be located within, the main vessel or may be formed by a partition in the main vessel. The pipe 8 may be arranged so that vapour is not directed on to the electrodes or screens may be provided for this purpose. Ignition may be effected by tilting, by the passage of current through a mercury thread or by the use of a high-resistance electrode which dips permanently into the liquid cathode. A number of anodes may be provided in arms which may be bent and fitted with control grids. In a further form, a metal vessel is provided with a liquid cathode 4, Fig. 3, six or twelve anodes 14 mounted in shields 16 and a hot cathode 2 arranged within a shield 18. The shields 16 are open at the bottom and on the sides facing the cathode 2. The electrode assembly is surrounded by a sleeve 19 which is secured to a ceramic member 20, is provided with drainage holes for the condensate, and has a sloping upper edge so that the length of the discharge paths are equal. Control grids are provided in, and connected to, the shields which may be supplied with a lead 21. The vessel may be connected permanently to a pump and the current in the auxiliary discharge may be kept small by grid control which is removed automatically when the load has been taken over by the solid cathode. A fuse or switch prevents the magnitude of the current in the auxiliary discharge from becoming equal to that in the main circuit. Minimum and maximum cut cuts may be arranged in one circuit and may be adapted to break both the main and auxiliary circuits. To maintain the current in the auxiliary discharge path constant, a rectifier is provided with a control grid 27, Fig. 5, which is connected to a tapping on a circuit which comprises a resistance 26, condenser 25 and rectifier 24 and is energized from the auxiliary circuit through a transformer 23. When the device supplies a smoothed rectified current, the control grid may be supplied from an alternator connected across a resistance in the auxiliary circuit. In another form, the rectified voltage across the resistance 28, Fig. 6 is fed, together with a negative bias from a battery 29 and an alternating voltage from a transformer 31, to a grid of a thermionic valve and the controlled anode voltage is supplied as shown to the control grid 27. The device may be used as a lamp.