ORIGINAL MESSAGE: (may be snipped)
On Tue, 28 May 2013 17:15:33 -0700, you wrote:
Thanks. I'm not the best metalworker, and I'm no kind of an engineer, so
my work doesn't
compare with that of some of the guys who regularly post here. But
hopefully it will be of
interest.
REPLY:
Hi Vic: I have three comments on the 4CX1000A amplifier which might be of
use to you.
1. The load cap appears to be a standard broadcast band variable. If that
is
so, it's voltage rating is right on the edge. As long as your SWR is 1:1
it
will probably work, but much above that and you can expect some arcing at
that power lever. Once an air variable arcs, small blisters form at the
point of the arc and it becomes even more prone to arc. If you ever
accidentally transmit into the wrong antenna, bye-bye load cap.
2. The plate choke is much too close to the tube's anode, IMO. I made this
mistake once and eventually the choke burned. Even though there is only a
few pF between the anode and the windings, at the extreme voltages
present,
a lot of current can flow especially on the higher frequencies. You might
get lucky and not have a problem, but watch for burned insulation on the
turns nearest the anode. Not only that, but you are inadvertently setting
up
a second parallel resonant circuit with that same capacitance and a
portion
of the plate choke. Again, you might get lucky, but beware.
2. The band switch looks awfully small for a legal limit amp. A REAL legal
limit bandswitch should be about four inches across and cost several
hundred
dollars. One should not skimp here. Ask Carl how many undersized band
switches he has replaced over the years. :-)
Otherwise, looks good. Having fun?
73, Bill W6WRT