The possibility of using the anode current to excite additional coils on the electromagnet of a magnetron oscillator and thus control the magnetic field is discussed, and a description given of experiments made with such an arrangement. The direct connection, in which the anode current assists the main magnetizing current, is shown to be of doubtful value; but the differential connection, in which the anode current opposes the main magnetizing current, when used in conjunction with a series resistance in the anode circuit, is shown to possess advantages as a generator of resonance oscillations. The number of turns on the coils and the magnitude of the series resistance can be so adjusted that the quotient of anode voltage to field intensity is approximately constant over the range of oscillation, which improves the operational stability and is likely to improve the frequency stability. The danger of the anode becoming overheated if a sudden reduction of the load on the valve takes place is also removed.
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