In article ,
John Doty wrote:

John Byrns wrote:

And I am glad you caught the two outer leg windings on Dave's
transformer that I missed, with that input it all makes sense now.

Note that in this kind of magnetic amplifier, the fluxes from the
reactance windings must cancel through the control winding. The reason
is that the control winding needs a lot of turns to make enough flux to
saturate the core with a small amount of current. On the other hand, the
reactance windings carry a lot of current, so they must have fewer
turns. Consider that this is a recipe for a transformer that puts high
voltage AC on the control winding unless the fluxes cancel there...

Yes, I understand that, in my first post on the subject I had proposed
that the S-W control reactor might have the two "secondary" windings
arranged on the two outer legs of the core so that it would operate as
you describe. Somehow I got the mistaken impression that Randy thought
all three windings were on the central leg of the core, which lead to me
thinking that all the windings were on the central leg when I first saw
the photograph, which doesn't clearly show the windings on the outer
legs because of the angle of the view. With the knowledge that the
secondaries are indeed wound on the outer legs, as I had originally
proposed, the mystery of its operation disappears, and Neil has even
provided a possible explanation for the usefulness of having the lamp
dim as the signal gets stronger.


Regards,

John Byrns

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