■ FIGURE 1. Principle of Operation.
■ FIGURE 2. Saturable Reactor.
The mag amp is an American
invention and has been used in heavy
electrical machinery regulators since
1900. In the 1940s, the Germans took
the American’s relatively crude device,
assigned their best scientists, invested
millions, and developed it into a faster,
lighter electronic tool competitive with
the vacuum tube in performance but
more simple and dependable. It’s also
much more rugged. A mag amp can be
made to be nearly indestructible.
The Germans used the mag amp
in electric brakes for trucks, streetcars, and locomotives. They used it
for high-voltage utility-power controls
and even for early computers.
Appreciating its indestructibility,
the Nazi military used it in gun stabilizers, in automatic pilots, and in mis-sile-guidance, including the rocket stabilizer and steering systems of the V-2.
After the war — like German rocketry itself — the mag amp emigrated to
the US, where it got further development
by enthusiastic American engineers. By
1951, a Navy engineer could write,
“Electronics engineers are now forced to
concede recognition of the magnetic
amplifier, as it has demonstrated its
value beyond question in many fields
dominated by the electron tube.”
that’s the definition of an “amplifier.”
A mag amp can be put in series
with any circuit carrying an alternating current and control that flow. No
external power supply is required to
run the device. The simple mag amp
is just a core of iron or ferrite with
some coils of wire wound around it.
One other basic component is
the rectifier. Today, rectifying diodes
are compact, easily available, and
cheap. The old selenium rectifiers
used back in the 1950s were large,
cumbersome, and expensive.
A variety of ferrite core materials
are also available to today’s builders.
With some spools of wire, a ferrite
rod, and a couple of diodes, you can
throw together a little high-frequency
mag amp on a Sunday afternoon.
Compare the construction challenge of a vacuum tube or transistor.
And the mag amp can handle voltages
and currents that you would never put
into the average transistor or tube.
How it Works
core’s permeability (its receptivity to
magnetism) can be varied by degrees,
thus controlling a larger AC flow.
Fully energized, the control coil
can reduce the permeability of the
core to zero, in which case the core is
said to be saturated. Then it becomes
so magnetically unresponsive it’s like
the core has been removed.
Figure 1 is a way of showing the
principle. With the core completely within the coil, the impedance to the flow is
high, permitting perhaps only a fraction
of a volt to appear across the load.
Pulling the core out causes the load voltage to rise progressively to 115. Since it
took only a few watts of muscular energy
to move the iron core within the coil,
which may, in turn, control several
horsepower, the device is an amplifier.
Figure 2 is another demonstration.
This qualifies as a saturable reactor.
This circuit could be for a dimmer for
theater stage lighting. Add a diode, and
you have a basic mag amp (see Figure
3). The larger coil is the control coil.
The smaller is called the loading coil.
The diode rectifier makes the load
current unidirectional, which assists
the control winding in saturation.
Considerably less power is now required,
making it a more potent amplifier.
This mag amp, however, will
function as a step-up transformer,
which would be undesirable since it
The mag amp, like the vacuum
tube and transistor, is an electrical
control valve. When a smaller circuit
controls another circuit’s larger flow,
The mag amp is a sort of variable
choke. It controls the impedance
(opposition) to alternating current in
a coil by controlling the magnetic
condition of the core on which the coil
is wound. This is done by energizing
another winding on the core called a
Depending on the
energy in the
control coil, the
■ FIGURE 4. Functional Mag Amp.
■ FIGURE 3. Mag Amp.
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