[R-390] VFO endpoint adjustment - stumped!

[Tim Shoppa]

OK, I'm stumped.

I'm putting my yellow striper back together. Right now the VFO covers
a range of 2.500MHz to 3.6MHz. At the low end it hits some sort of
apparent mechanical stop. Didn't hit anything at the high end because
I don't need to turn it that far :-). It is supposed to cover 2.455
to 3.455 MHz (and with 25kHz of under-run it ought to go to 2.430 MHz)
just as a reminder.

Even though it doesn't span the right range, the linearity is pretty
good, and in the first ten turns it is always within 0.5kHz of being
on the money.

I look in the Y2K manual, but the endpoint adjustment screw illustrated
there does not match my unit physically. There is a plug-screw in mine,
but it's on the left hand side, outside the triangle frame as seen from
the front. The one in the Y2K manual is shown as being inside the
triangle frame and a bit on the other side.

Inside the plug-screw, I find some sort of slug that can be turned
with a 3/8" screwdriver bit. The slug seems to be hollow and probably
brass. Turning it does nothing, doesn't budge the frequency at all.

There is another access hole, inside the triangle frame, that has a bunch
of little set screws in it that slowly scroll past as I turn the dial.
I think these are obviously the linearization screws. I do not want to
screw up the linearization of this PTO, I am very happy with it as is.

Oh, and I pulled the metal rectangular cover from the box, and found
some resistors.  Hmm, that 2.2k resistor looks a little suspiciously
brown, better check it out.... actually 8K!!! This makes the score on
this radio for a total of seven 2.2K resistors that were too high
in value by hundreds of percent! (Almost all of them in the plate lines).
So I fixed that.

So how do I adjust the endpoint on this PTO? No maker's label on the outside,
but there is a refurb sticker from Raytheon, indicating a service date
of Feb 7, 1976. At one point I brought it up and I think the suggestion
was that it was a Motorola? I could be recalling that incorrectly.

Tim KA0BTD