[R-390] 390() vs 390(A), R-391

[John KA1XC]

> Poll -- how many of you guys have R-391's with working autotuners?  How
many
> with non-working ones?  How many unknowns?  Actually, I think it was Paul
> who rebuilt his '391, right?
>
> Barry

Well Barry, I've got two of the 391 beasties, one has been given some
attention and is working well as a 390, the other is still waiting in line.
Both were missing the locking keys and the state of the autotune is TBD. On
the one I worked on I did remove and open up the autotune boxes in the
front - and yikes, talk about a box of complicated mechanical doodads. They
of course were smothered in old dried grease so I had some fun scrubbing the
mechanisms clean with WD-40 and oiling up the little oiler sponge inside.
That's about as far as I got, after that I re-installed them and told myself
I wouldn't attempt any further until I learned a lot more about how they
work.

I also thought the MC detent in the 391 was very well done; it is a much
better engineered mechanism than the little spring steel weenie that wears
out in the 390 and 390A . Too bad they didn't use that design in all the
radios.

Without a functioning autotune I would say a R-391 is definitely second to a
R-390 in desirability due to the fact that the autotune mechanisms add a lot
of extra drag to the KC tuning. It gives you about 1/4 turn of easy turning
before it kicks in, and then the drag is much more noticeable.

Another item lacking here is a good 28 VDC power supply with enough oomph to
drive the motor. Ideally what I'd like to get or build is a fully metered
regulated supply with adjustable current limiting, that way I'd set the
current limit to just above what the motor normally draws and the power
supply would go into current limit if something went wrong with the autotune
control and the motor hit a stop. It'd probably need at least 10,000 uF on
the supply output to take care of the motor start-up surge current too.

Since I needed locking keys I bought a set from Hank Arney and they look
real sweet. I tried inserting them into the knobs and into the innards of
the autotune and they thread in nice and smooth to a point but then appear
to bind up before the locking handle makes it down to flush with the knob
face. Is this normal or do they really need to be screwed in very hard all
the way down? Since I don't have any experience with using the autotune
section I'm taking it real cautious here, don't want to beak anything! I'd
appreciate some advice on this.

thanks,
John