[R-390] R390/URR Gear train

Sat Jun 8 17:49:05 EDT 2019

Ahhhh!  Now I see.  That big preload gear (the brass one) preloads that gear
connection through the gear with the four holes.  Wacky.  "Pretty sneaky
sis!"

Thanks for the pic Don!  I've got it all back together and am synchronizing
the Genva drive.  Running into some small issues in that the TM calls out
"figure 76" for verification of the switch contact positions and there is
not figure 76 in the TM.  Arrgggh.  I have two versions, they both refer to
figure 76 and neither has it.

Thank you kind sir!
John

-----Original Message-----
From: Don Heywood <wc4g at knology.net> 
Sent: Saturday, June 8, 2019 5:28 PM
To: jgedde at optonline.net
Subject: Re: [R-390] R390/URR Gear train

OK, John, I turned one of my receivers up on end and can see that those
gears with the four holes will mesh with the small gear on the PTO shaft
when you reinstall the RF deck and mate it with the KC knob mechanism. I
took a picture and attached it.

-----Original Message-----
From: jgedde at optonline.net
Sent: Saturday, June 08, 2019 4:12 PM
To: 'Don Heywood'
Subject: RE: [R-390] R390/URR Gear train

Hiya Don,

I get the preload thing there are about a half dozen other ones I already
did in putting it back together.  This one is different as it doesn't seem
to be able to lock itself.  What I mean is this...  All of the other split
gears get preloaded then the preloaded gear engages itself in another gear -
a single one so as to be able to spring open within the gear profile of the
regular gear and eliminate backlash...  The key thing with this is that the
split gear spreads between teeth on a single gear.  Easy.

Now, the one I'm asking about preloads but engages in to*two* separate
gears.  One preload gear for each of the two normal gears.   In other words,
the preloaded gear engages to another split gear except that gear doesn't
have springs nor is the split laying on top of each other.  There's a spacer
between the two gears.  It's very strange.  If you look at the bottom of my
picture you'll see a steel gear with four big holes in it.  Directly behind
that gear is another just like it.  There's a spacer between them.  One of
those two gears is connected to the shaft and the other can freely rotate on
the shaft.  Above that gear to the left is the split gear.  It's much bigger
than all of the other split gears and is made of brass.  It has no holes in
it apart from where the springs are located.  See it?  That gear can be
preloaded but each of the sprung pair engages to a separate gear and the
preload just unwinds!  That's what's throwing me.

John

-----Original Message-----
From: Don Heywood <wc4g at knology.net>
Sent: Saturday, June 8, 2019 2:59 PM
To: jgedde at optonline.net
Subject: Re: [R-390] R390/URR Gear train

John, I know the section of Pearls I referred you to is for the "A" model
but the preload information still applies, in fact a lot of the pearls also
affect the older model we work on. There has been a section added just for
this older radio the R-390/URR!
I can't see any number 79 in your picture, but if the gears have a set of
springs between them then they need to be preloaded.
This preloading procedure takes practice, slide one gear carefully to
disengage from the gear it meshes with leaving its mate engaged, then using
your thumb and forefinger slide the gears to overlap a tooth or two and
while holding this relationship slide the first gear back onto the mating
gear. If the springs come loose reinsert them with fine needle nose pliers
of forceps.

I am only trying to help. I had to learn all this the hard way.

Don

-----Original Message-----
From: jgedde at optonline.net
Sent: Saturday, June 08, 2019 2:30 PM
To: 'Don Heywood'
Subject: RE: [R-390] R390/URR Gear train

Hi Don and thanks,

You pointed me to the R390A pearls and I'm working on a R390.  The R390A
from what I can see, doesn't even have the gear I'm talking about.  There
are a bunch of preloaded gears, but it's the one in particular I'm referring
to.  It doesn't seem to have any way of holding preload.  Is it some kind of
sprung thingamabob to prevent excess force on some part of the mechanism?  I
understand the purpose of the split gears to eliminate backlash, but this
gear has nothing to lock to since the gears it meshes with are both freely
rotatable.  It's hard to explain.  In my photo, the two spaced gears on the
part marked 79 can both rotate independently.  It wasn't preloaded to start
with either yet everything seemed to work...

John

-----Original Message-----
From: Don Heywood <wc4g at knology.net>
Sent: Saturday, June 8, 2019 2:07 PM
To: jgedde at optonline.net
Subject: Re: [R-390] R390/URR Gear train

Hi John, please go to: <http://www.r-390a.net/Pearls/> and look under the RF
deck mechanical section and then do a work search (cont. f) for "preload"
and see all the data. This preloading is to keep tension on the teeth to
preclude any backlash when tuning back and forth, hence - no slop - have fun
, 73, Don WC4G

-----Original Message-----
From: jgedde at optonline.net
Sent: Saturday, June 08, 2019 1:39 PM
To: r-390 at mailman.qth.net
Subject: [R-390] R390/URR Gear train

I took apart my geartrain for cleaning this morning on the 390.  No end to
solidified lubricant.  Now I'm putting it back together.  I noticed before I
took it apart that the big brass split gear (part 73) wasn't preloaded.
Nowhere in the manual does it say how this should be done or what it's
supposed to preload.  What is this for?  It meshes with another gear
assembly (79) that has two gears separated by a spacer.

I've attached a photo of what I'm asking about.

John

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