Re: Loosely coupled transformer windings

"John Popelish" <jpopelish@xxxxxxxx> wrote in message
news:g-edncoX_6xheRHanZ2dnUVZ_hSdnZ2d@xxxxxxxxxxxxxx
Think E cores with center or one leg ground
off to make a gap.

My drawing probably wasn't too clear, but there was an air gap in the middle
leg. (It looks like a washer.) I figure that I can wind the 3 windings,
then increase the air gap to reduce the coupling to the secondary until,
under load, it drops from 1000V of "turns-ratio" voltage to about 100V-200V
of "loaded" voltage, while still keeping close coupling between primary and
feedback windings, (or two halves of a centre-tapped primary for push-pull
driving).

There are E core shapes made that have
all 3 legs the same cross sectional area for this purpose.

I don't quite follow what you mean here.

And, of course, you could add an external inductor in series
with a tightly coupled secondary and get a very similar effect.

Yep, I've also been thinking about that. It would make starting easier, too,
especially if I adopted a method of shorting across the second side of the
heater filaments to heat them, then open that circuit to dump the series
inductor's energy across the tube for ignition, similar to mains operated
fluoros.

Incidentally, in the end I'll also add heater windings, which should have
reasonably close coupling, but one thing at a time, I reckon.

.... Steve


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