A symmetrical transistor oscillator with low second-harmonic distortion

Summary form only given, as follows. A transistor oscillator with good amplitude and frequency stability and a low second-harmonic output is desirable to supply the excitation power for a second-harmonic-type magnetic modulator. In the circuit presented here, the required stability is obtained by designing the circuit to be as independent as possible of the transistor characteristics. The grounded-base transistors operate to transfer a fixed current alternately from one side to the other of a tuned center-tapped transformer. The transistors act as switches, either essentially open circuit, or conducting at negligible collector voltage. Hence, the switched current can be determined by an external circuit. The special emitter switching circuit is designed to provide rapid switching and to deliver constant emitter driving current essentially independent of the emitter characteristics and the driving voltage. A low value of second harmonic, less than 0.01 per cent, is obtained by the balanced nature of the circuit and by adjustment of the emitter switching circuit to provide equal on-off periods in each transistor. Drifts in this on-off time caused by changes in emitter resistance are reduced by a large stabilizing resistance in series with the dc portion of the emitter switching circuit.