Magnetic Amplifiers

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sr1200

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http://en.wikipedia.org/wiki/Magnetic_amplifier

Read through this article today and thought it kind of interesting.  Has anyone ever used a mag-amp and what kind of sonic characteristics does it have?  I'm assuming they aren't horribly favorable or they were just forgotten after advances in solid state amplifiers.  Could this be a kind of "effect" of some sort (novelty) if the sonics are poor?  Or, are they decent and just a relic of the second world war, long forgotten?
 
Back in the '60s on my first technician job, we were de-bugging a new SOTA dc to dc switching power supply. Old hat now, but back then cutting edge. IIRC the novel power supply circuit used a magnetic amp in the current limiting section of the supply. Something like when the current in one winding of the mag amp saturated the core, the impedance of the other winding was influenced and that was used to starve a drive stage and current limit the output (or something like that??). 

My recollection and description may be a little off, this was almost 50 years ago, and I was a junior electro-mechanical tech at the time. I wasn't even an electronic tech (yet). My job was mainly to unsolder and replace parts blown up by the project engineer, but i quickly learned my way around the circuit by troubleshooting and repairing the blown up parts.

Mag amps are hard to blow up, so I didn't have to pay much attention to them.  Transistors back then were very easy to blow up. The IC brain of the switching supply was a very early linear regulator IC (LM100) tricked to be bi-stable and switching.

I suspect magnetic amplifiers are an old school technology that made sense to use instead of active circuitry back when gain stages were very expensive. These days electronic circuitry is probably cheaper and easier to use.

JR
 
Mag amps are better suited for low-frequency applications. Achieving 20Hz-20kHz would be a major feat.
THD is enormous and NFB is almost impossible to implement. There have been very-high power very low frequency systems built for military purpose, where SPL was the main object but distortion not a concern. In the 60's, the army was evaluating them in comparison with pneumatic amplifiers. I believe the project was nicknamed Jericho.
To my knowledge, nothing came out of it. The Berlin wall has never been threatened by it.  ???
 
I have a vague recollection of a TV program many yeas ago about a French weapon project to generate high SPL 7Hz audio and project it at the enemy. Apparently 7Hz is the resonant frequency of the chest cavity and the weapon was intended to disrupt  the  major organs inside it. Charming people the French.

Cheers

Ian
 
I remember some protests of the U.S. Navy by Greenpeace  (or  similar) about low frequency  experiments that were disturbing  whale communication..  Probably 10 years ago or so.
 
http://www.americanradiohistory.com/Audio-Magazine.htm
September 1952 (14 MB PDF file)
page 42 (pg 44 in PDF)

  "ELECTRONIC ENGINEERS are beginning to accept the fact that competitors to the electron tube are not only a reality but are here to stay.
  "A considerable amount of material has been published on magnetic amplifiers, most of which pertained to servo and other electro-mechanical control applications. Very little data is available on high-speed applications, ...."
 
After enough wordage to fill many pages, he comes up against the need for a HIGH power HIGH frequency power source. (You can't make audio with 60Hz wiggles.) In 1952, this would be A TUBE, giving very little advantage over just throwing a couple 6L6 directly in the audio path.

Magnetic amplifiers need very special magnetic properties. Arnold's lab worked overtime turning out trial alloys and treatments. Nevertheless mag-amps remained a niche until they faded away.
 
Come to think of Lars Lundahl, the transformer manufacturers from Sweden.
He made a Magnetic Amplifier project many years ago.
Here's something to read about it.

http://www.auditorium-23.de/MagAmp/MagAmp_Prospekt.pdf

http://www.auditorium-23.de/MagAmp/MagAmp.html

--Bo
 
Well, now theres a point of discussion!  That's awesome.  I was thinking more of a colored alternative to a tube for use in a pre or something (low power) but that... I think I wanna hear that.  Great find!
 
sr1200 said:
Well, now theres a point of discussion!  That's awesome.  I was thinking more of a colored alternative to a tube for use in a pre or something (low power) but that... I think I wanna hear that.  Great find!

I would like to hear one too.. just wonder how and where without building it? It's interesting from the effect perspective.
 
I remember being most intrigued by the website of my local club / music venue back in the early 90s. They boasted an obscenely loud P.A. using "magnetic amplifiers". It didn't sound great - Bose speakers not much above ear level and horn bass bins either side of the stage. Frankly, too loud!

But it made me look up magnetic amps in the library. I didn't quite follow it despite being on the first year of my EE degree. Turns out they were Carver "Magnetic Field Power Amplifiers" - not actually mag amps at all. Don't you just love marketing words...
 
sr1200 said:
Well, now theres a point of discussion!  That's awesome.  I was thinking more of a colored alternative to a tube for use in a pre or something (low power) but that... I think I wanna hear that.  Great find!

My recent Gyraf G21 works like this in some sort of half-hearted way: Using rectified signal to generate DC enough to saturate a winding on transformer core, and thereby attenuate/clip AC signal. No gain though  ::)

Jakob E.
 
ruffrecords said:
I have a vague recollection of a TV program many yeas ago about a French weapon project to generate high SPL 7Hz audio and project it at the enemy. Apparently 7Hz is the resonant frequency of the chest cavity and the weapon was intended to disrupt  the  major organs inside it. Charming people the French.

Cheers

Ian

I saw that TV program too! Here's a clip from it:
https://www.youtube.com/watch?v=M9mB0OGWkYE




;D
 

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