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Search for magnetic amplifier circuit

  1. Nov 24, 2012 #1
    I had the pleasure of using and seeing the schematic of a two stage magnetic amplifier that was used to control the magnetic field of a large electromagnet, during my graduate work in superconductivity at the University of New Orleans. It had a large DC gain and with a resistor for feedback produced a gain of near 1000. The DC input, I presume was from a spinning gauss meter coil in the magnetic field, some few millivolts and the output of the amplifier was some volts, used to control the magnet (3 phase AC input)power supply.
    As I remember the AC power source for the magnetic amplifier was a few volts at an audio frequency and there were two sets of reactors (maybe two toroids). The output from the first set was fed as input to the second set to produce the large power gain. The intermediate connection did not to my knowledge involve any nonlinear parts such as transistors or diodes and the output was a voltage source proportional to the input voltage similar to a DC op-amp circuit. Unfortunately I did not copy the page and it is likely lost from the University of New Orleans Physics Department. I am trying to figure out how this worked and possibly recreate a crude replica. The final output of my (school's) amplifier was DC. The device was a commercial bought circuit about the size of a book.

    Supposedly the Germans used amplifiers of this type on their naval guns during WWII.

    Memory is a drawing of what I remember of the schematic that I saw in college. DCAmp1a is almost at the level I am building at home. Navserva is part of a navy device which is three stages and more sophisticated than I can understand or reproduce. My school's device had a minimum of non-magnetic parts, and, I believe no diodes.
    If you can find anything on this or even advise on experiments please help.

    Attached Files:

  2. jcsd
  3. Nov 24, 2012 #2
    About 40 years ago went through tests and finding information on saturable reactors and magnetic amplifiers. Would hesitate to use either one now. This is what I remember.

    Saturable reactors do not use rectifiers.
    Magnetic amplifiers use rectifiers.
    Saturable reactors are constant current devices. My interpretation.
    Magnetic amplifiers are constant voltages devices. My interpretation.

    Signal transformer brand transformers make good saturable reactors or magnetic amplifiers. Most other brand transformers use different core steel and do not make good saturable reactors or magnetic amplifiers.

    The book Reference Data for Radio Engineers, fifth edition by ITT has a section on magnetic amplifiers. It's a great book and I recommend that every engineer should have one.

    Following are some articles on magnetic amplifiers. The articles are ancient and may not be available.

    Mag Amps, PCIM July 1998.

    Magnetic Amplifier Control for Simple Low-Cost, Secondary Regulation, Unitrode Corporation.

    Magnetic Modulators, by Sidney L. Silver, Electronics World, June 1964

    Magnetic-Amplifier Design, Communications and Electronics, May 1958 issue

    Design of High Frequency Saturable Reactor Output Regulators, by Charles Mullett, P.E., Mullett Associates, Inc., High Frequency Power Conversion, session 9, 1986 tutorial.
  4. Nov 25, 2012 #3

    jim hardy

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    Magamps are coming back as feedback elements in switching power supplies.

    They were the reliable alternate to vacuum tubes for important equipment until theintegrated circuit op-amp came along

    http://www.themeasuringsystemofthegods.com/magnetic%20amplifiers.pdf [Broken]
    was linked on tnhis forum a year or two ago..

    Search on magnetic amplifier combined with

    Voltage Regulator
    Westinghouse Magastat

    and see what turns up

    Magnetics Inc makes cores..

    old jim
    Last edited by a moderator: May 6, 2017
  5. Nov 25, 2012 #4
  6. Nov 25, 2012 #5

    jim hardy

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    A fun link, that SparkBangBuzz..

    He observed that the addition of rectifiers makes it self-saturating, which is the key to good gain.

    Also one wants a good core, like strip wound or toroid of hi mu metal.
    Those little c-core power transformers shouldn't have worked very well
    but are a great demonstration of principle.
  7. Nov 26, 2012 #6
    I want to know exactly how to demonstrate the improvement obtained with rectifiers. I have two hi mu toroids but must wind the wire by hand. I would like to use 6 or 12 VAC 60 Hz. I have a scope and lots of parts.
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