GB631393A - Improvements in and relating to thermionic valve oscillators - Google Patents

Abstract

631,393. Valve generating circuits. CLIFFORD, F. G. Jan. 9, 1947, No. 722. [Class 40 (vi)] A wide range oscillator with low harmonic content has a combined feedback and output transformer which comprises two coupled inductors L<1>, L<2>, one tuned by a parallel capacitor C<1> and the other by a series capacitor C<2> in accordance with the equations where k is the coefficient of coupling between L<1> and L<2> and Wo is the oscillatory frequency, the resistive load into which the oscillator works being placed in series with the series-tuned circuit. The Figure shows an oscillator in which the primary of the output transformer is tuned by capacitor C<1> and the secondary by capacitor C<2>, the oscillator working into the resistive load R<2>. The frequency of oscillation may be adjusted by ganging the tuning capacitors C', C<2>. The tuned transformer operates as a frequency-selective device and discriminates against harmonics of the fundamental oscillatory frequency, thus lessening the harmonic content of the output waveform. The output impedance and voltage level may be made more constant over a wide frequency range by shunting the inductor L<1> by a resistor R<1> as shown in the Figure. In a modification, Fig. 2 (not shown) the voltage across the resistive load is fed back into the cathode circuit of the valve the connections to one of the inductors being reversed so that the conditions for oscillation are still maintained.