State of the art of magnetic amplifiers in Japan

Self-saturating magnetic amplifiers are being built widely for all industries and for service equipment. Although the source frequency is generally 50 or 60 cps (cycles per second), occasionally 400 cps or 10 kc is used to improve the figure of merit. The maximum output is 3,000 kva (kilovoltamperes) in the saturable reactor, and the minimum input is 10−16watts in the magnetic-modulator type of amplifier; the former is used for the temperature control of an electric furnace, and the latter for the instrumental servomechanism. External feedback amplifiers are still used in variable amplification, and those of the fast-response type are appreciated in servo amplifier use. As core materials, oriented silicon-steel is suitable for magnetic amplifiers of large output capacity since oriented 50% nickel (Ni), 50% iron (Fe) alloy is expensive, and molybdenum-Permalloy is preferable for small input amplifiers. Magnetic amplifiers are used at present for noncontact relays, operational amplifiers in analog computers, magnetic-type oscillators, self-excited a-c generators, etc. They are expected to find application in digital computer elements, in special-configuration magnetic circuits, and in unique circuits in which magnetic devices are combined with semiconductor elements.