[R-390] CU-714/SRA-22 ramblings

[AI2Q Alex]

Just a word of thanks for the many kind replies from R-390 listers on my
newly acquired CU-714/SRA-22 surplus antenna tuner, part of the old URC-32
radio set. I sholuld've recognized the nomenclature of this beastie from all
the work I did on the USS Albacore sub, but for some reason that thought
eluded me until this afternoon.

Anyway, after studying the wiring I can see that it's an L-network, with the
vacuum capacitor motor also driving a hefty switch, so it can be set up with
the cap in either series or parallel with the coil.

In the original usage, whether the cap is in series or parallel can be
indicated with a lamp or LED, as they bring out the switch extra contacts
for that purpose.

The unit's other two motors drive (a) the coil itself, and (b) the tap on
the coil. So, by using either motor I can set the inductance and where I
want to tap-down on the inductance.

Also, as I see it, if I put a manual switch on the RF leads, and re-wired
the RF feed and output, I could reverse them, which might add some
flexibility to its use in the shack, making it more adaptable to many more
kinds of end-fed antennas and verticals.

The motors are marked 115V 60 Hz, so I tested them out tonight using a
variac and isolation xfmr. The capacitor-drive motor works FB as-is, and can
be reversed by switching pole connections on the motor itself.  The coil
motor and coil-tap motor required a phase-shift capacitor to make them run.
I grabbed an old 1 uFd bathtub cap, rated at 600-V, and that worked just
fine. They can be reversed with switches to reverse the phase of the applied
115 V (swap the leads with a toggle switch).

With a few switches, I should be able to make this puppy work in any config
needed. Also, I haven't tested them yet, but the coil and coil-tap motor
geartrains have pots hooked up to them, so with a DC power source of a few
volts I should be able to drive a meter or two so that I can see how far the
coil and coil tap has moved. Sort of like on some Yagi rotator boxes.

I'm thinking that this would be a good thing to tune my present top-loaded
phased 80-meter vertical array. All I need is one more CU-714/SRA-22 (if I'm
lucky), one for each vertical. Then I'd be able to QSY from the fone to CW
portion of the band, right from the shack, without having to go outside on
cold winter nights or during storms. Gotta feed the R-390, R-390A, and R-392
properly.

I hope present-day equipment is built this good, so that it works well
against those SOBs Bin Laden and Saddam (Madass spelled backwards) Hussein.

Vy 73, AI2Q, Alex in Maine, where the wind is howling tonight with 45 MPH
gusts

.-.-.