[ARC5] Spinner knobs - tuning gear

[Mike Morrow]

> The spline shaft is not so easy. The ID would probably have to be EDM'd
> unless it were made in two pieces. You could probably broach the spline
> into the ID of a short length of thick walled tube, then brase that to a
> piece of shaft.

For the typical ham-type requirements, it was once common to use a short
piece of 1/4-inch OD soft copper tubing that could be tapped onto and over
the spline on one end, and some common control knob secured on the other
end.

The A.R.C. 6743 (a.k.a. MC-137) seems to be a lot more common than it should
be, since few of these sets made use of the tuning knob anywhere in the system.
Yet it is not rare to find these for about $30 on ebay, which is much cheaper
than anyone could make an equivalent.

The communication receivers R-25, -26, and -27/ARC-5 were supplied with the
A.R.C. 9554 tuning key attached under the tube cover, along with the small
control box tuning dial (ID-27, -28, -29/ARC-5).  This key was used to set
receiver tuning pre-flight, after which it would be reversed to provide
a cover over the spline port for common lock-tuned receiver installations.
The navigation receivers R-23* and R-24/ARC-5 (and all ARA and SCR-274-N
units) were not supplied with the A.R.C. 9554 since they were never lock-tuned.
The A.R.C. 9554 does not fasten very tightly nor securely to the spline.
and it has a small knob diameter.  Thus it is an unsatisfactory substitute
for the A.R.C. 6743.  The now typically empty threaded circular base found
under all non-VHF AN/ARC-5 receiver tube covers is the storage base for
that receiver's A.R.C. 9554, not the A.R.C. 6743 as some suppose.

What I have never come across in four decades of looking is the A.R.C. 7491
LOCAL ANT-LOOP CONTROL for the R-23* and R-24/ARC-5 receivers.  The
A.R.C. 6743 will work there, but it's just NOT what was intended! :-)

Mike / KK5F