[R-390] added the IEC line filter

[Tim Shoppa]

> Can not emphasize the importance of everything
> properly grounded in a crowded shack!

Yeah, I remember when I was a kid and my heathkit
transceivers always gave me a pretty hefty tingle whenever
I touched the chassis :-).

I've got a more serious ground system than a skinny wire
to a water pipe now!

If I look at my non-R390A rigs (mostly dating from the 50's and
60's) I see they often have symmetrical line filters (and a few
have symmetrical fusing, that is fusing both "hot" AND "neutral",
that was popular for a couple of decades it seems.)  But generally
the AC hot-to-ground current through the filter cap
is circa 1 or 2 mA so they do not
trip the GFCI by themselves... but in concert they do!

Tim.