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Saturable Reactor realized with two transformers

This video shows a quick experiment I did while I was studying saturable reactors that were used for modulation during the early years of AM radio, before the advent of vacuum tubes. This is an ad-hoc magnetic amplifier; a type of saturable reactor. A typical magnetic amplifier, or mag-amp, has a complex magnetic circuit and has at least three windings. Nevertheless, it is possible to realize one using two power transformers. That is what I have done here. I used filament transformers (120V primary, 12.6V secondary.) I tried several configurations, and some definitely worked better than others. In this configuration, the input (control) circuit consists of the secondaries of the transformers wired out of phase and connected to a variable DC power supply. The output (load) circuit consists of the primaries wired in series, in phase, and in series with a 25W incandescent lamp and the mains (120VRMS.) With no current flowing in the secondaries of the transformers, the primaries simply behave like large inductors. This limits the current to the light bulb to a very low level. As the secondaries are wired out of phase, their respective induced voltages cancel out. This prevents the induced AC voltages from interfering with the DC power supply. As DC current from the power supply is ramped up through the secondaries, the current induces a magnetic field in the transformer cores. This increasingly saturates the core material. The saturation drops the inductive reactance of the primary windings and allows a much larger AC current to flow through the light bulb. This provides a means of controlling a large AC current with a smaller DC control current. The circuit yielded 6dB of power gain and 35dB of voltage gain. Much higher levels are possible with purpose-built magnetics. This circuit was thrown together with stuff laying around. This over 100 year old technology may seem archaic but is still used in extremely demanding applications. A mag-amp has no moving parts, can work at high temperatures, and is immune to vibration. More importantly, their function is unaffected by neutron radiation. This makes them very useful in nuclear applications.