[R-390] Squirrely PTO

[Tim Shoppa]

OK, you guys may remember my dissected PTO. It's mostly back together,
but now I notice something else:

If I tune continuously in one direction, then the frequency is nice
and smooth.

If I reverse and tune continuously in the other direction, then
the frequency is nice and smooth after a small fraction of a turn.

But... for a small fraction of a turn (say a few hundred Hz which
would be like a degree or so) if I wiggle it back and forth it sounds
"squirrely". Seeing how this only happens when I reverse direction,
I'm guessing this is some form of backlash.

"Squirrely" means that if I'm tuning through a carrier it does
not smoothly go up and down, but jumps around by like 100 Hz
or so from smooth. In the "reversing zone" I can turn the knob a bit
with no noticable frequency change, and then it jumps a lot (maybe
100 Hz).  After the reversing zone it seems to be nice and smooth.

Pulling the covers off and looking inside I see no obvious anti-
backlash spring. There is a ring holding tight the PTO slug to
the threaded shaft, and maybe that's supposed be under tension
to make the assembly be anti-backlash?

What is the "official" anti-backlash mechanism for this PTO? It's
a Raytheon-refurbed Cosmos by my best reckoning.

If I go to my other 390A (also a Cosmos PTO) the behavior is not
nearly so squirrely. There may be a very small amount but it's
possibly my wrist :-).

Or is it not anti-backlash, but something that the right grease
cures? I've rebuilt Ten-Tec PTO's and the usual cure for everything
there is a few new plastic parts and magic grease. I didn't really
understand what I was doing but I was just following Ten-Tec's
directions. My feeling is that plastic pieces and grease is not
the answer for my 390A's PTO, but I will appreciate corrections!

Oh, as to overall PTO alignment, after I "jumped a turn" the range
was correct and with a little tweaking of the endpoint and a couple
of the setscrews it's nice and linear, to within a few hundred Hz
end-to-end. I do seem to be at the very very end of the endpoint
adjustment range: if I need more range, is the endpoint inductor
the inductor that folks remove a turn from? I remember hearing about
the procedure but didn't really relate to it, having never torn into
the PTO when I was reading!

Tim.