GB475530A - Improvements in or relating to thermionic oscillation generator circuits - Google Patents

Abstract

475,530. Valve circuits for generating oscillations. STANDARD TELEPHONES & CABLES, Ltd., JACOBSEN, B. B., and TERRY, V. J. May 22, 1936, No. 14549. [Class 40 (v)] Variations in the frequency of currents generated by a thermionic oscillator circuit with variations in the supply current are prevented with the circuit shown in which the primary of the feed-back transformer 7 is tuned and directly connected to the grid of an amplifier valve 4 and is coupled to the anode circuit of the valve 3 through a condenser 9 and resistance 8 by arranging that the ratio of the transformer is such that the amplitude of the oscillations generated is limited by the flow of grid current in 4 which takes place at a lower amplitude than that at which grid current would flow in 3, and providing a small variable condenser 15, settings of which can be found experimentally which make the frequency generated independent of variations in the sources of supply 2, 1. Usually, these settings are different, but if the transformer 7 includes a core of a material such as soft iron dust, the permeability of which varies with frequency, circuit settings can be found that give frequency stability with variations in both sources of supply. A further advantage of such a core is that its temperature coefficient may compensate that of the main condenser 10. In a modified circuit, Fig. 2, in which the oscillator valve 3 is biassed by a grid leak instead of by a resistance in the heating circuit, an adjustable condenser 17 for giving stability is provided in shunt to resistance 8 and optionally a resistance 25 is included in series with 15. Where it is found that negative values of capacity are required for the condensers 15, 17 to give the desired result, they are connected instead at 17a and 15a. The Specification indicates the relative values of some of the circuit elements.