GB142474A - Improvements in the use of thermionic devices for producing frequency harmonics of electric oscillations - Google Patents

Abstract

142,474. Western Electric Co., (Assignees of Vennes, H. J.). April 28, 1919, [Convention date]. Frequency, changing.-By inserting a high impedance, such as an ohmic resistance, in the plate circuit of a thermionic valve, the characteristic is changed from the type of curve shown at 1, Fig. 1. to that shown at 2, which gives greater distortion of an impressed sinusoidal wave when the valve is overloaded, with a consequent freer production of harmonics. The distortion is most marked in alternate half-cycles, and both odd and even harmonics are produced. The ohmic impedance also serves to stabilize the action of the valve. In the arrangement shown in Fig. 3, alternating current from a generator 6 is impressed through a transformer 8, 9 on an amplifying valve 10, the output circuit of which is connected to the grid circuit of a distorting-valve 20. The potential of the grid of this valve can be adjusted by a switch 20<1>. The circuit between the valves 10, 20 is bridged by a capacity-inductance loop 26, tuned to the base frequency of the generator 6, and having therefore a practically infinite impedance to this frequency but a small impedance to other frequencies, so that a substantially pure sinusoidal wave is impressed on the valve 20. The plate circuit of this valve includes an ohmic impedance 25 large compared with the internal impedance of the valve. The output circuit of the valve 20 is connected to the grid circuit of an amplifying valve 30, the connexion being bridged by an inductance 34 which has a higher impedance for the harmonics than for the base frequency, so that the former are impressed preponderatingly on the valve 30. The output circuit of this valve is connected to the work circuit through a transformer 36, 37. The filaments of the valves 10, 20, 30 are heated by a common battery 15, and their plate circuits are supplied by a common battery 17 through inductances 18, 24, 33. Blocking-condensers 19, 27, 35 prevent the passage of direct current in undesired paths.