Basics of Magnetic Amplifiers 

"Like with any Circuit there is a big difference between the proof of concept and the useful high performance implementation" yeah tell that my boss

I graduated in 1979 with an Electrical Engineering degree. We had exactly 1 hour of vacuum tube review, lol. I was fairly well prepared in basics to work on Mag Amp controls in steel mills. I had to pick up control principles on the job unfortunately. I was privileged to see the evolution as mag amps were replaced by analog electronic drives, then digital drives and master computer controls were added as the overall system manager. And PLCs rapidly replaced the extensive relay panels. I think it was a great time to be an EE. As I worked in old mills there were many mixed mag amp/plc/digital drives/and master computers that were still in use to 2006. I got pretty good at digging up old vintage parts and figuring replacement parts. The upgrades we installed were over decades. It was challenging and satisfying. I even had cranes designed in 1890s lol! Mag Amp mfgrs like GE, Westinghouse, Allis Chalmers, Jocelyn Clark, and more. Your article is very interesting! PS, it wasn't just power, it was used for regulating dc motor speed, torque, and tension loops. I toured a WW2 submarine mueeum and the mag amps were clearly present.

Some forty years ago, I encountered a magnetic amplifier in an industrial CO2 laser used for metal sheet laser cutting. It was used to regulate a high voltage supply that powered the electrodes on both sides of the laser tube.

I hadnt seen nonlinear magnetic saturation used for amplification, but one of the coolest things Ive seen is M0BMU's electromechanical VLF receiver that uses magnetic saturation to make an rf mixer for listening to SAQ at ~17 kHz

I’ve seen these in schematics, not intended for power regulation or amplification, but rather as an electrically variable inductor for passive LC filtration. There’s no other (non-electromechanical) method of varying inductance with an electrical signal, and varactors don’t have as large a range and are probably more temperature sensitive. I can see this being especially useful for RF circuits, where the required coil size is much smaller, and you don’t have the ability to make active filters and virtual inductors without expensive high-end semiconductors. Not just for VCAs and VCFs, but for VCOs too. I don’t know how linear they are compared to JFETs for amplifiers and active filters, but you can always use an extra winding for feedback.

I have not come across a magnetic amplifier myself - as far as I can remember - but I first learned about them with regard to old radio transmitters from about 100 years ago. It seemed to be the only feasible way to control the amplitude modulation at kW power levels back then.

Industrial/Commercial welders used the magnetic amplifier into the 1980's - my personal experience was troubleshooting and repair of the Miller 330 AP-B/Goldstar and Aircrafter 330. The former controlled the DC bias current via a 200W rheostat, the latter through a triac. Heavy, reliable machines!

Only you to present such a span of topics without missing a beat, Tank you Fez!

woah man, I was looking for some understandable thorough explanation of mag-amps for weeks and best I could find was a 50s or even older thesis... thanks for the vid!!!!!!!

I finally understand 💡how this old PC-AT power supply was regulating the secondary voltage outputs. Thanks a lot !!

Great video and I hope there is a sequel on magnetic audio amplifiers, preferably sans crossover distortion. Magnetic amplifiers are preferred in cases where reliability, robustness, longevity and efficiency matter much more than cost of building, volume and weight of the device.

Magnetic amplifiers were used in the french nuclear submarines (called SNLE in France) for amplifying the current delivered by power nuclear sensors because of their reliabilty. There was a feedback scheme for improving the linearity.

The Fred A. Leuchter Associates electric chair design used a saturable reactor to regulate the output current to 5 amperes. The instruction manual described it as a magnetic amplifier. There was a 6A circuit breaker "to protect the load" which I always thought was a particularly eerie turn of phrase.

A mag amp is a “static variable inductance in series with a load”. This was the description in an instrumentation manual. I saw two basic uses for these. In instrumentation to amplify DC signals. When the instrumentation was designed the choice was tubes or mag amps. Tube type DC amplifiers are a challenge and much less reliable than mag amps. The other use was in static exciters to provide up to 50 amps to the field winding of a turbine generator. The alternative was an amplidyne In addition to the control and gate windings, most mag amps also have a feedback winding and a bias winding. Adjust feedback and bias to set zero and span

The U.S. Navy, in the mid 1950's, at least... used magnetic amplifiers to very successfully replace syncho systems that had previously used control transformers, and electronic amplifiers. There were many benefits over the purely 'electronic' systems of the day. Like being lighter, and more robust in harsh environments shipboard. It provided syncho isolation, and very fast, and stable, transient response. Remember, this was in the vacuum tube, zinc plated, world of the 50's

In Polish radars, in the 80s/90s, in modulator systems for controlling the magnetron, transformers with a so-called "rectangular hysteresis loop" were used. The core of the pulse transformer was "under-magnetized" by an additional winding with regulated current. This has nothing to do with signal amplification, but there is an analogous shift in the core hysteresis characteristic.

Круто! Так редко про магнитные усилители вспоминают))) Молодец что такой материал подготовил. Я к стати использую магнитный усилитель для управления двигателем вентиляции, тиристорный слишком шумный, магнитный работает достаточно мягко.

I built a magnetic amplifier using a pair of 1 amp Variac cores. Each was wound with half the number of turns that the 120V original winding had. Cores were stacked & 10,000 turn control winding was wound through both. I used this to control the current to 8 fluorescent lamps on wall of discotheque, which were modulated to the music. It is important that the 2 cores be matched & the number of turns on the power windings match to the turn, or AC will back up into the control circuit.

Mag amps were used extensively in Navy ships to control gun turrets. When they became unstable, the triple 9" or 12" guns could shake the whole ship and send the fire control tech running for the anti-hunt pots.

An informative video with follow-up reading , you are too kind . An interesting video as always , thank you .

Yes in a power supply for a backup battery charger! A very old design for an older aircraft.

people always seem amazed by these things... i find it more amazing how much technology has been left by the wayside... that our education system lacks in outlining the basics... the name "saturable reactor" is a far more... self explanatory name. you just apply a dc magnetisation current to "saturate" the core, at which point theres no lenz reactions or "inductive reaction" to an AC current. the coil acts like a plain wire with only DC resistance. another closely related device is the "peaking transformer"... using core materials of two different saturation curves, to produce pulses from a sinusoidal or other waveform. it pays to collect as many old books as possible... the ignitron, kenotron, thyratron, and pliotron may be obsolete, but often, those books that deal with them break down many otherwise complex subjects into simple and easily understood basics... which then makes it far easier to digest other seemingly unrelated topics... we got where we are by riding on the shoulders of extremely intelligent men. its a bit like opening an old desk fan the other day... oh my, it has an inductor. which were also common in ceiling mount speed controls. early on, it was cheaper and more reliable than any capacitor of the time. but now its always a capacitor used as they are so cheaply made, and the dielectrics so much better. ptfe and polyethylene versus waxed paper, etc...

Mag amps were popular in nuclear submarines for control because of the extreme reliability. Not sure if newer designs still use them.

12:27 I think it is still commonly used in cheaper and lower power ATX power supplies for PCs. It generally goes by the name of 'group regulation' although I could be mistaken, it is possible that in such cheap PSUs there is no form of regulation of all auxilary rails and reliant on tight enough coupling and low enough resistance of components to ensure stable enough voltage under most load conditions that the rails remain within tolerance.

MANY PC power supplies had a magnetic amplifier on the 3.3V rail, with a core made of a special material.

Magnetic Amplifiers were used in Aircraft instruments (Auto Pilots) Smiths SEP 2 , still flying in RAAF older aircraft in the late 80s when I worked as an Aircraft instrument maker. They were bullet proof. Pun intended.

That's how old telephones worked, isn't it? Thanks! Nice channel, btw!

I believe the term "magnetic amplifier" is somewhat ambiguous. Rather, a "saturable reactor" is more definitive, cheers.

PS All right I've seen your page and the other comments, now you put here the basics, it's ok and I realy like all.

You may be able to use Variable Inductor (VarInductor), much like Variable Capacitor (Varactor), to tune VCOs and filters. Specially for high power applications.

I have used equipment with saturable reactors (which I guess are magnetic amplifiers) , but this is for very high power (+500kW switching), used to vary inductance very quickly.

If you haven't seen a Mag Amp in action, take apart an ATX pc power supply, it's a 3v3 coil

I expected you show us an audio amplif working with only transformers and control windings in cc. So, when it wil be the next episode? Be engineer, not only teacher! ;) Good luck!

I think these were (at one time at-least) commonly used to dim airport runway lights.

Interesting work. Thank you.

Really excellent content. Keep up the good work OM. 73

An incredible book around this topic, if you want to see a lot of interesting topologies and design your own transformers suitable for magnetic amplifiers, is the book "Wzmacniacze Magnetyczne" written by Gabler, Haškovec, and Tománek!!! It can be found in most Warsaw-pact languages even, I have a Polish translation. It is from the time when active research was still done in the subject, so you'll find a lot of alternative information and topologies that may not have been published on the internet yet. I really recommend anyone to get it if you're interested diving into the material :-)

12:00 yes, it is still used in PC's power supply, aka cross regulators (is the big core inductor plenty of wires with almost all output voltages at the output side of the P.S.U.

I see this having a really nice use in a homemade variable power supply for vacuum tubes. The one you made is perfectly good as-is, but why not make it more efficient by using such a mag-amp instead of an ordinary linear regulator? I'll try this out sometime!

very interesting. i can imagine that old dimmer switches work that way but i am not old enought to know.

noob question: could crossover distortion be avoided by applying a low DC bias to the AC side of each transformer? Of course with bypass capacitors (could we still call them "coupling" here?) to block it from getting where we don't want it. Also an unrelated question: how to I check the saturation characteristics of a certain transformer? The datasheets I find online don't provide them. Should I look for the datasheets of inductors with the same cores like you suggested? For example I have some EI14 1:1 isolation transformer in transit and would love to try out a mag amp. I wanna build it for a unique kind of guitar distortion effect.

First [community] theater I worked in used saturable core realtors to control the stage lights. The console had an array of slider potentiometers hooked up to the dimmer cabinet, delivering a 0-10vDC voltage to each lighting channel. Buzzed like a hornets' nest when the lights were brought up. Cool retro'. Doubtless the waveform was ratty as h311.

Yes i've seen it in the seventies for a speed regulator for elevators.

Магнитные усилители широко применялись в системах Г-Д для управления электроприводами. В электрических экскаваторах. Там применялись двухтактные дифференциальные преобразоватетипа ПДД 1,5 на экскаваторах ЭКГ-4,6, ЭКГ-5. И ПДД 1,2 на экскаваторах Э - 25 серии Э-2503, Э-2505, Э-2508, Э-2508СА. И на металлообрабатывающих станках для управления электроприводами. Были еще и злектромашинные усилители типа ЭМУ которые выполняли те же функции.

Seasonic S12iii uses magamps to regulate its 5 and 3.3V rails. i havent seen any other PSUs using it for both minor rails

There are still magnetic voltage regulators (Magnetischer Spannungskonstanter) in the market, at least in Germany.

Excellent!

greate video. Thank you.

Excellent! ❤

Fascinating subject, and well presented, as always. I wonder could this principle be used to make a "voltage controlled" low pass filter? Changing the inductivity of the filter L component should give a different response. Also, could saturating that core from your example be done by a simple permanent magnet moved into proximity?

3:07 in this setup, how much of the inductance decrease is caused by the power supply circuit actually shorting out the secondary side as you decrease the series resistance? At 250mA, there is only ~12 ohms on the secondary.

Hi can you make a video about Parametric Amplifiers? (They are used as LNA at really higb frequencies). I think it would be interesting. Thanks

Nice explenation. Mr. Ben-Yaakov uploded the video about usage of this variable inductor idea to provide lower losses in power converters working with much higher input voltages (Buck)/smaller load. Probably variable frequency is still an easier solution.

Thank you.

Those poor poor waveforms. Lol Thanks for a great video!

heell yeahhh Some Sony devices had a magnetic amplifier for its feedback between the main and secondary of the switch mode power supply, with unusually shaped cores.

Haha turn on subtitles and watch the opening , he mentions saturation of the transformer and then talks of magnetic ampli fires as per subtitles haha I guess that’s the result with sustained saturation

Thanks and 👍

From what I understand.. under the right conditions inductors behave like transistors..

This shows that working with magnetic is just working in mine field of non linearity that noway but blow up something ....

Will an ML4818 (Fairchild) phase shift modulator provide accurate current control to such similar loads ...with proper f.b. loops and some additional circuitry from its outputs to generate a load frequency synced "ac controlled signal" ? ...instead of the normal "dc".....perhaps even core saturation may be tightly controlled.

In this episode: Speedy Gonzales invents the 'Mag Amp'.

Can I make a variac by this method?

Nice 😘

🌟

👍👍

was it used before BJT transistors were invented?

Seems a significant amount of people never heard of magnetic amplifiers. IME, either their engineering school sucked, or they did computer engineering and spent most of their time playing video games and drinking beer. IMO... if you don't understand D.C. currents, superimposed on A.C. currents, in inductors and transformers, you don't understand either.

Quantum computing modules.....

Magamps were used in many places in the navy. They are robust.