A new theory of the magnetic amplifier

The paper presents a completely new theory of the magnetic amplifier with a finite load resistance and a low-impedance signal circuit. The analysis assumes that the B/H curve for the core material has a constant initial slope, followed by abrupt transition to zero slope at the saturation level. From this basic assumption, flux waveforms are derived and equations are developed for the magnetomotive forces operating at every instant in the cycle for a transductor with any degree of self-excitation. Analytical expressions are thence derived for the output characteristics, and the particular conditions of zero self-excitation and full self-excitation are examined in detail. Further expressions, both in full and in simplified form, are obtained for the current amplification and time-constant of a transductor, since these quantities are of considerable importance in design work. Because of the idealized form assumed for the B/H curve, the theoretical characteristics are not completely realized in practice; but the theory provides a basis for improved methods of design, and explains certain important phenomena (such as the variation of the current amplification with change of the load resistance) which are not revealed by more elementary treatments of the subject.