[AMPS] Swinging Choke Theory

[Peter Chadwick]

Rich says:

>What does it take to convert a swinger to fixed L?

Depends. Some chokes, just undo the clamping screws, and if the E and I
laminations are not interleaved, put in a piece of card. The inductance goes
down, but changes less. If the E and I laminations are interleaved, a bit
more work to de-interleave them, and stack as E's and I's with a bit of card
or paper in there. If it's a hermetically sealed or potted in varnish choke,
tough. Take it to a hamfest and try unloading it there! Or try it in an
experimental PSU. After all, ham radio is supposed to be 'self training in
the art of wireless telegraphy'. The usual caveats about playing with HV
PSUs apply, though.

BTW, the capacitor is not just any old thing lying about. It can have high
AC voltages across it, and fairly high AC through it. Watch the VAR ratings.
I find that generally, large paper caps are OK. If it gets warm, change it
for something bigger. You're probably only looking for something around 0.1
to 0.2 microfarad in a 60Hz supply area. It's also worthwhile going for
negative lead filtering - that gives a bit less insulation strain on both
choke and capacitor insides to metal case.

If you can get a non-swinging choke, so much the better! 

My experience with tuned choke PSUs has been very good. Incidentally, if you
negative lead filter, you get enough volts across the choke that you can
rectify it for negative bias.

73

Peter G3RZP


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