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The magnetic amplifier colloquially known as a "mag amp" is an electromagnetic device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to vacuum tube amplifiers where robustness and high current capacity were required. The magnetic amplifier was most prominent in power control and low-frequency signal applications from to about , when the transistor began to supplant it. Combinations of transistor and mag-amp techniques are still used.

Visually a mag amp device may resemble a transformer , but the operating principle is quite different from a transformer — essentially the mag amp is a saturable reactor. It makes use of magnetic saturation of the core, a non-linear property of a certain class of transformer cores. For controlled saturation characteristics, the magnetic amplifier employs core materials that have been designed to have a specific B-H curve shape that is highly rectangular, in contrast to the slowly tapering B-H curve of softly saturating core materials that are often used in normal transformers.

The typical magnetic amplifier consists of two physically separate but similar transformer magnetic cores , each of which has two windings: a control winding and an AC winding. A small DC current from a low-impedance source is fed into the series-connected control windings.

The AC windings may be connected either in series or in parallel, the configurations resulting in different types of mag amps. The amount of control current fed into the control winding sets the point in the AC winding waveform at which either core will saturate. In saturation, the AC winding on the saturated core will go from a high-impedance state "off" into a very low-impedance state "on" — that is, the control current controls the point at which voltage the mag amp switches "on".

A relatively small DC current on the control winding is able to control or switch large AC currents on the AC windings. This results in current amplification. Two magnetic cores are used because the AC current will generate high voltage in the control windings. By connecting them in opposite phase, the two cancel each other, so that no current is induced in the control circuit.

The magnetic amplifier is a static device with no moving parts. It has no wear-out mechanism and has a good tolerance to mechanical shock and vibration. It requires no warm-up time. The windings of a magnetic amplifier have a higher tolerance to momentary overloads than comparable solid-state devices. The magnetic amplifier is also used as a transducer in applications such as current measurement and the flux gate compass. The reactor cores of magnetic amplifiers withstand neutron radiation extremely well.

The gain available from a single stage is limited and low compared to electronic amplifiers. Frequency response of a high-gain amplifier is limited to about one-tenth the excitation frequency, although this is often mitigated by exciting magnetic amplifiers with currents at higher than utility frequency. The bias and feedback windings are not unilateral and may couple energy back from the controlled circuit into the control circuit.

This complicates the design of multistage amplifiers when compared with electronic devices. Magnetic amplifiers were important as modulation and control amplifiers in the early development of voice transmission by radio. Magnetic amplifiers were also used to regulate the speed of Alexanderson alternators to maintain the accuracy of the transmitted radio frequency.

The alternator's frequency limits were rather low to where a frequency multiplier had to be utilized to generate higher radio frequencies than the alternator was capable of producing. Other core materials, such as ferrite cores and oil-filled transformers, would have to be developed to allow the amplifier to produce higher frequencies. The ability to control large currents with small control power made magnetic amplifiers useful for control of lighting circuits, for stage lighting and for advertising signs.

Saturable reactor amplifiers were used for control of power to industrial furnaces. Small magnetic amplifiers were used for radio tuning indicators, control of small motor and cooling fan speed, control of battery chargers. Magnetic amplifiers were used extensively as the switching element in early switched-mode SMPS power supplies, [5] as well as in lighting control.

Semiconductor -based solid-state switches have largely superseded them, though recently there has been some regained interest in using mag amps in compact and reliable switching power supplies. PC ATX power supplies often use mag amps for secondary side voltage regulation.

Cores designed specifically for switch mode power supplies are currently manufactured by several large electromagnetics companies, including Metglas and Mag-Inc. Magnetic amplifiers were used by locomotives to detect wheel slip, until replaced by Hall Effect current transducers. The cables from two traction motors passed through the core of the device. During normal operation the resultant flux was zero as both currents were the same and in opposite directions.

The currents would differ during wheel slip, producing a resultant flux that acted as the Control winding, developing a voltage across a resistor in series with the AC winding which was sent to the wheel slip correction circuits. Magnetic amplifiers can be used for measuring high DC-voltages without direct connection to the high voltage and are therefore still used in the HVDC -technique.

The current to be measured is passed through the two cores, possibly by a solid bus bar. There is almost no voltage drop in this bus bar.

The output signal, proportional to the ampere turns in the control current bus bar, is derived from the alternating excitation voltage of the magnetic amplifier, there is no voltage created or induced on the bus bar. The output signal has only a magnetic connection with the bus bar so the bus may be, quite safely, at any EHT voltage with respect to the instrumentation.

Instrumentation magnetic amplifiers are commonly found on space craft where a clean electromagnetic environment is highly desirable. The German Kriegsmarine made extensive use of the magnetic amplifiers. They were used for the master stable element systems, for slow moving transmission for controlling guns, directors and rangefinders and train and elevation controls.

Magnetic amplifiers were used in aircraft systems avionics before the advent of high reliability semiconductors. They were important in implementing early autoland systems and Concorde made use of the technology for the control of its engine air intakes before development of a system using digital electronics. Magnetic amplifiers were used in stabilizer controls of V2 rockets.

Magnetic amplifiers were widely studied during the s as a potential switching element for mainframe computers. Mag amps could be used to sum several inputs in a single core, which was useful in the arithmetic logic unit ALU. Custom tubes could do the same, but transistors could not, so the mag amp was able to combine the advantages of tubes and transistors in an era when the latter were expensive and unreliable.

The principles of magnetic amplifiers were applied non linearly to create magnetic digital logic gates. That era was short, lasting from the mids to about , when new fabrication techniques produced great improvements in transistors and dramatically lowered their cost.

A voltage source and a series connected variable resistor may be regarded as a direct current signal source for a low resistance load such as the control coil of a saturable reactor which amplifies the signal. Thus, in principle, a saturable reactor is already an amplifier , although before 20th century they were used for simple tasks, such as controlling lighting and electrical machinery as early as In radio pioneer Reginald Fessenden placed an order for a high frequency rotary mechanical alternator from the General Electric Company capable of generate AC at a frequency of kHz to be used for continuous wave radio transmission over great distances.

By Alexanderson added a magnetic amplifier to control the transmission of these rotary alternators for transoceanic radio communication. The experimental telegraphy and telephony demonstrations made during attracted the attention of the US Government, especially in light of partial failures in the transoceanic cable across the Atlantic Ocean.

Magnetic amplifiers were extensively used in electricity power generation from the early s onwards. They proved durable and reliable. Many are recorded in service through the mids and some are still in use at older generating stations, notably in hydroelectric plants operating in northern California. In the s, Robert Carver designed and produced several high quality high-powered audio amplifiers, calling them magnetic amplifiers.

In fact, they were in most respects conventional audio amplifier designs with unusual power supply circuits. They were not magnetic amplifiers as defined in this article. They should not be confused with real magnetic audio amplifiers, which also exist.

From Wikipedia, the free encyclopedia. Sams and Co. Self-saturating Magnetic Amplifiers. New York: McGraw-Hill. The nature of ferromagnetic materials results in far less damage from nuclear radiation than is done to semiconductor materials. This study was made at a total integrated neutron flux of 2. Popular Electronics. Retrieved The electronic watchdogs that keep the Triton's powerful nuclear plant operating without a hitch are magnetic amplifiers — almost hundred of them are used for this critical job.

Pressman Switching Power Supply Design. May []. The magnetic amplifier is not new — the principles of the saturable core control were used in electrical machinery as early as although they were not identified as such.

Magnetic Amplifiers — Principles and Applications. New York: John F. Rider Publisher. Library of Congress Catalog Number Magnetic amplifiers were developed as early as in the United States. At that time they were known as saturable reactors and were used primarily in electrical machinery and in theater lighting.

Fundamentals of Magnetic Amplifiers. Indianapolis, Indiana: Howard W. Library of Congress Catalog Card Number: The use of magnetic forces for amplification is not new; a survey of its history shows that although the device was not known as a magnetic amplifier at the time, it was used in electrical machinery as early as Alexanderson, The accomplishments and life of E. The Evolution of Power Electronics.

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INTER-M PA60 MIXER AMPLIFIER 60W/4-8, 100V

A budget range of units with a wide range of applications in industrial, commercial and recreational installations. All units carry a 5 year parts guarantee. The amp has 6 inputs including 5x balanced mic dBu or line level dBu , and 1x twin phono RCA , dBu 2kohm input. A telephone system input paging output from phone system not BT line , 0dBu 10kohm.

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The magnetic amplifier colloquially known as a "mag amp" is an electromagnetic device for amplifying electrical signals. The magnetic amplifier was invented early in the 20th century, and was used as an alternative to vacuum tube amplifiers where robustness and high current capacity were required. The magnetic amplifier was most prominent in power control and low-frequency signal applications from to about , when the transistor began to supplant it. Combinations of transistor and mag-amp techniques are still used. Visually a mag amp device may resemble a transformer , but the operating principle is quite different from a transformer — essentially the mag amp is a saturable reactor. It makes use of magnetic saturation of the core, a non-linear property of a certain class of transformer cores. For controlled saturation characteristics, the magnetic amplifier employs core materials that have been designed to have a specific B-H curve shape that is highly rectangular, in contrast to the slowly tapering B-H curve of softly saturating core materials that are often used in normal transformers.

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Magnetic amplifier

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