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Most folks believe that first came the vacuum tube and right on its heels came its successor, the transistor. Not really. Another control technology, came in between. This is the technology of the magnetic amplifier.
The mag amp was developed by U.S. and German engineers in the 1940's and 50's. What is the relevance of the mag amp to experimenters and engineers today? For one thing, while the tube and transistor are of esoteric manufacture, a mag amp can be built by anyone. The mag amp is indestructable compared to the fragile transistor and vacuum tube.
In
the 1940's and 50's, the magnetic amplifier
was not just an experimental dream languishing in some inventor's
notebook. Nor was this ingenious technology sitting unexploited in
patent archives. By the 1950's, the magnetic amplifier was in
manufacture in a
number of versions in the U.S., and had a clique of
boosters, including many electronics engineers.
This document, unusually passionate and well written for a military tech manual, is their promotional brochure. Evident today only in some motor-control and power-supply regulator applications, the mag amp not only can regulate but can magnify, modulate, switch, pulse-generate, invert, convert, multivibrate, phase shift, and multiply. Mag amps require zero maintenance, can be made indestructible and EMP-proof, and can handle up to 200,000 amperes
Navel electronics engineers are beginning to accept the fact that a competitor to the electron tube, in the power and control field, has not only penetrated their domain but is here to stay. When first confronted with this device, they simply ignored it as being an impostor, too slow, cumbersome and inefficient to be taken seriously. Even when it started to strut in a new cloak of self-saturation and promoted itself to the rank of magnetic amplifier, it was still ignored by American electronic engineers. The device finally gave up in disgust and proceeded to Germany for physical reconditioning and a post-graduate course in social education.
The electrical-machinery people early visualized the advantages of the device as attested by the almost universal application of this static control for rotating equipment.
Electronics engineers are now forced to concede recognition of the magnetic amplifier, as it gas demonstrated its value beyond question in many fields previously dominated by electron tubes.
The significance of this development in relation to Naval engineering is better appreciated when it is realized that this component is applicable to almost everything that rotates or moves on a fighting ship: throttle controls on the main engines; speed, frequency, voltage, current and temperature controls on auxiliary equipment; fire-control, servo mechanisms and stabilizers for guns; radar and sonar equipment; pulse-forming, sweep multivibrator circuits for radar, loran, and transponder equipment; and computers, and course-and-speed plotters to verify the results.
The device is ideally suited to submarine and aircraft equipment because of the extreme voltage fluctuations of the prime power sources. Numerous countries have contributed to its evolution. ...
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History
The magnetic amplifier is not new; the principles of the saturable-core control were used in electrical machinery as early as 1885 although they were not identified as such.
Saturable-core devices have been used, principally in heavy electrical machinery, in the U.S. since 1900. The U.S. Navy has been using them to a limited extent mostly as static control instruments in rotating equipment during the past eight years. Development beyond this perimeter into the electronic field has been retarded in the U.S. primarily due to the reluctance of our engineers to experiment with a new device, especially in view of the excellent performance experienced with current electron tube equipment.
Many engineers are under the impression that the Germans invented the magnetic amplifier. Actually it is an American invention. The Germans simply took our comparatively crude device, improved the efficiency and response time, reduced weight and bulk, broadened its field of application, and handed it back to us.
It was mainly the improvement in processing magnetic material and the introduction of selenium rectifiers that led to the wide use of magnetic amplifiers by the Germans.
The German navy used the device in its master gun stabilizers. Their air force used it in automatic pilot and ground-approach systems. They also used it in servo and frequency-control systems for long-range rockets, blind landing aids, and to regulate the fuel flow in relation to atmospheric and ram pressure in some types of guided missiles. They also applied the device as cathode followers, replacing electron tubes in computer circuits. The German army had started to apply it to the V-2 rocket stabilizer and steering system. ...
From Magnetic Amplifiers, Another Lost Technology, by the US Navy, edited by Trinkaus, published in print 2000 to 2011 by High Voltage Press.
A Mag Amp Project
see the complete feature article
in Nuts & Volts, Feb. 2006
The
green coils are loading coils, wound
in opposite directions. The red coil is the control coil. A DC signal
on the control coil controls oscillating high energy in the loading
coils. The mag amp is a sort of variable choke controling a circuit
by varying the permeability of a magnetic core.
All three coils are wound on a core of 1/2" x 6" ferrite rod (#33), slipped inside acrylic tubing for insulation. Loading coils have 860 turns of #26 enamel in 13 layers, with turns of electrical tape between layers. Control coil wound with 400 feet of #30 enamel. Nylon fender washers complete the spools. The loading coils are frequency-specific and resonant at 180 kc. Diodes are 1N4008, 1-KV, 3-amp.
Schematic: See the basic circuit in Figure 4 in
Magnetic Amplifiers PDF