[R-390] R-391 help

[Barry Hauser]

Hi Paul & list

Yup keep those ovens off.

The '391 uses the same round connector as the R-390/URR (notice I went out 
of my way not to write "non-A").

I don't remember the pinout -- it's in the manual, but the 4 pins are 2 for 
AC, one for ground and one for 24 vdc.  The ground is common I think.

The autotune 24 vdc should be supplied with "amp-le" current -- at least 5A, 
maybe 7A due to the surge factor.

Also, you should pre-check the autotune mechanism as much as you can without 
powering it up.  If it looks as though it's gunked up with dried 
out/hardened lube -- don't bother, it won't work and could cause damage to 
apply power to it.  Also check under the lower part of the front panel -- as 
I recall, you can see without removing the panel.  In particular, look at 
the full length of the worm drive shaft which traverses about 2/3rd's the 
width of the receiver.  Look for bronze shavings or powder where the shaft 
passes through 4 or five bosses in the "spider" -- cast metal frame.  There 
are "oilite" bearings (sintered porous bronze "permanently lubricated" 
bushings" at each point.  The shaft should rotate when the mechanism is 
turned (locking keys tight on both KC and MC knobs), but there should be no 
lateral play.  If there is, that means the bearings are shot.  If the 
mechanism binds up when power is applied it may then grind up the bearings 
if they aren't already worn.

(Don't ask me how I know this ;-) ... or should I say ;-(

Be sure you go through the synchronization procedure in the manual that 
involves turning the worm drive with a bristol wrench through a hole on the 
right side (when you are facing the receiver, not "left" as it says in some 
manuals).  There are also two adjustments -- one on each autotune head. 
It's explained in the manual.

Also, to avoid a heart attack or close simulation thereof, when you apply 
the 24 vdc, first make sure the locking keys on the tuning knobs are loose 
and the channel selector is on the same channel as the number showing in the 
little window, otherwise it will immediately actuate.  (A difference or "not 
equal" condition is what triggers the sequence.)

If you're game, then tighten down the two keys -- not too tight, but snug --  
and change channels but brace yourself and be ready to cut DC power from the 
source -- e.g. switch on the DC supply.  Even when it works right, it makes 
a loud racket -- basically driven by geared down Hamilton Beach motor (and 
many have Hamilton Beach tag on the motors) -- basically same as the motor 
used in a blender or mixmaster on steroids.

Again, be ready to pull the plug on the DC.  Most of these need overhaul --  
complete disassembly, cleaning and relubing.  The two control units -- one 
on each of the MC and KC controls -- contain pawls -- stacks of metal pieces 
with hook ends which engage notches in disks which are also stacked on 
common shafts.  The metal pieces have to slide freely against each other for 
the whole thing to work.  That's easily defeated by hardened, sticky lube 
and unless someone has already overhauled the thing and operated it 
recently, it's a virtual certainty that it won't work.  However, it may well 
power up -- and try to self-destruct.

Common failure mode - starts up with a loud whine and a clatter (normal) and 
the knobs and counter start turning.  Comes to the end of the travel of one 
or both ranges (KC and/or MC) but tries to keep on going, banging up against 
the end of the 10-turn stops.  It is conceivable that it can do damage or 
partially de-synch an RF deck.

I have two of them.  First one - loaded with grease as if someone thought 
they were topping up the rear end of a half ton truck.  Second one -- bronze 
bearings shot.  I think the second one started to work, nearly doing two 
cycles, before the two bearings nearest the motor ground up and the gear at 
the end of the shaft that mates with the motor or nearest intermediate gear, 
kicked out of mesh and started grinding.  Would go in one direction, but not 
the other.

The general problem is that many of the autotuners on the '391's have not 
been in use in a long time.  Many previous owners just operated them as a 
"non-391" and let the autotune mechanics languish.  Or ran it once and 
didn't care for the noise and clatter.  The vibration also runs against the 
grain -- wear and tear on tubes (and 3TF7) as well as on fine mechanical and 
electronic alignment work.  Shakes everything up.  Interesting to watch 
though -- once or twice.

Paul Anderson overhauled one of these a couple of years ago and was writing 
an article for the Hollow State Newsletter.  We hope to pick it up again, 
finish it and publish on the HSN website.  He had the procedure all written 
up, but the stumbling block was the photos needed to get it across.  The web 
site venue should help with that.

Barry



> Folks,
>
> Just fired up a beautiful R-391 from a local friend who kept his radios in 
> immaculate condition.  I carefully brought it up with a variac power 
> supply that had a voltmeter and an ammeter.  I was wondering why the 
> ammeter kept bouncing from 1.4 to over 2A until I realized that the 
> crystal ovens switch was ON.  That's a bad thing... keep the ovens off 
> folks....
>
> Now the next challenge is to get the tuning mechanism operational. 
> Anybody out there have a connector for the 24V tuning side of this beast?
>
> Best regards,
>
> Paul W0AD
> Minneapolis
>
>
>
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