Toroids and Magamps

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henry crun

Toroids and Magamps

#1 Post by henry crun » Sun Sep 06, 2015 9:51 am

Aircraft electrics run on 400Hz ac, rather faster than terrestrial ac mains, so that transformers are much lighter in weight. The transformers, rather than using E and I laminations, are toroidal. The core is a wound-up strip of magnetic material, and the windings are threaded around that by special windings machines. Ours were in a facility 'down the ditch', the local slang for Kingsditch Lane. The machines were operated by a gang of very coarse women. Woe betide any fresh-faced young apprentice who ventured into the winding shop, they would push his willie into a small-size glass milk bottle and tickle him until, aroused, he was unable to remove it.


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By using the right number of turns the toroids could be run very near to magnetic saturation. Applying additonal dc field would push them into saturation, resulting in greater current on one ac voltage peak. By using two in opposition, you get a dc in, ac out amplfier. Totally solid state, just two toroids. Of course the ac out was a weird shape, but no matter, it was sufficient to drive servo motors. The motors had an ac field and the variable ac input from the magamp, so reversal of the dc into the magamp would produce reverse rotation of the motor. Much of the Vulcan and Trident autopilots were constructed of magamps, dead reliable and free from parameter drift.

The magamps used on the Vulcan were about three inches cube. The case was plastic with connection tags attached, and the cores were suspended inside in foam rubber. Occasionally there were production faults and one of my apprentice tasks was to diagnose what had shorted and where, so I got adept at digging into foam rubber without severing the very fine wires.

Using four toroids and very few electronic components made a dc in dc out magamp. The Trident magamps consisted of four toroids less than two inches diameter potted into an aluminium 'bathtub' with a small tagstrip on top to hold the electronic bits.

Now a lost art, but then a remarkably effective way to do the job.

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Re: Toroids and Magamps

#2 Post by Wodrick » Sun Sep 06, 2015 10:10 pm

You is talking the dark language of Smiths, Henry. The Comet Autopilot was full of Mag Amps of course, all I remember is heavy and 'Plessey Plugs'

When doing my Autopilot and to a lesser extent Instrument licenses I dreaded a written or even an oral question on Mag Amps. They were in the syllabus, but the examiner just brushed over them, "nobody uses them any more do they ? " and I don't think you will ever work on Trident. Right on both counts.

Did come across one in quite a modern installation once, think it was a yaw damper but long forgotten which a/c

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Re: Toroids and Magamps

#3 Post by Blacksheep » Mon Sep 07, 2015 2:10 pm

The most phantasmagoric Magnetic Amplifer system I ever worked with was the computer that lay at the heart of the Gnome Engine Electrical Fuel Control System. It controlled the power transmitted to the Whirlwind and later the Wessex and Sea King main rotors by automatically adjusting the fuel delivery to the Gas Generator(s). It balanced gas generator speed, free-turbine speed, power turbine inlet temperature, selected rotor speed and collective pitch anticipator inputs to maintain a constant main rotor speed whatever collective and cyclic pitch inputs the pilot applied - obviously working very hard when hovering in extreme conditions.

I use the past tense relative to my own experience, Wodrick, for it is still operating in Westland Sea Kings to this very day - 58 years in service.

The world's first fully autonomous electronic engine control system it was a marvel of 1950s de Havilland electrickery.

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Re: Toroids and Magamps

#4 Post by Avtrician » Mon Oct 05, 2015 11:01 am

I used to work on similar stuff, the AC regulator for for the Mirage. I was one of the few guys in Malaysia who could understand how it worked..


The light dimmer in Movie theatres was a Magamp.

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