Improvements in or relating to thermionic valves and thermionic valve circuits

摘要

359,041. Capacitance measurements. CROWTHER, H. L., Royal Aircraft Establishment, South Farnborough, Hampshire, and SMITH, C. H., 29, Mount Park, Carshalton, Surrey. July 18, 1930, No. 21759. [Class 37.] The arrangement shown in Fig. 2 provides means for measuring the anode-grid capacity of a screengrid valve, the screen grid 1 being connected to the filament circuit through a variable inductance 3 in parallel or series with a variable resistance 11. The screen grid is also connected through condenser 9 and switch 10 either to the anode or control grid circuit, the latter being coupled at 14 to an amplifier comprising a heterodyne detector and telephones. The anode circuit is coupled to a source 13 of radiofrequency. Inductance 3 is adjusted to give zero signal in the telephones and the anode-grid capacity is given by the expression:- where L1, L2, L3 are the required inductance values with the switch 10 in each position and C is the capacity of condenser 9. Fig. 3 shows a practical embodiment of the method exemplified by Fig. 2, the screen grid 1 being connected through circuit 3, 11 to the earthed screening system 15. By means of two switches 16, 18 and two condensers 17, 19, the screen grid may be connected either to the anode or control grid circuit. The same effect may be obtained with four-electrode valves other than the screen-grid type.