[R-390] For the r-390 wishlist -- Things for the R-390/URR
Cecil Acuff
chacuff at cableone.net
Fri Dec 16 10:27:53 EST 2005
Hey Folks,
I've done a few in the last year and to tell you the truth they are much
easier to work on than the "A". (MHO) Mainly because they don't require so
much concern about the capacitors used when manufactured. I have spot
checked in the few I have done and found maybe one or two I have replaced
due to leakage. One was the top hat looking tantalum that is often found in
the "A" all corroded up. It was strange because I had not seen one of that
type in an R-390 before..only in the "A". There are 4ea. 47 ohm resistors
that need to be replaced usually. I upgrade those from 2 watt to 5 watt.
And that's about it. I have never found the filter caps to be out of spec
but it's because they used high quality oil bath caps for filters. (I'm not
saying they don't go bad...just I haven't come across that yet) It's a good
thing I haven't found them bad because I don't know what you would ever do
to replace them and not make the radio looked hacked.
As far as the gear train....the fabled "GREEN GEAR"....is of no real use!
You don't need it to keep the world from coming apart. The only purpose it
serves as far as I am able to tell is to keep the Veeder-Root counter in
sync with the gear train if removing the RF deck for a simple repair and
dropping the deck back into the chassis. If you are doing a restoration you
will probably remove the counter anyway.
I sat for hours one night on the bench pondering the purpose of the green
gear with the RF deck out and the green gear in place. I studied and
studied and finally through caution to the wind and pulled the "GREEN GEAR"
off and went to work. I figured if I had overlooked some obscure function
of the gear it would become obvious upon reassembly. It never did and all
worked fine. The biggest "Gotcha" if there is one is to mark the band
switch in some way to get it back to a known position upon reassembly and
sync of the RF deck.
I start by setting the radio at the prescribed 2.000 Mc and begin
disassembly. I take a spring loaded hand punch and put a dot on the two
brass gears that mesh on the band switch. Kind of a timing mark of sorts
for you old car buffs. Now you have 90% of the battle under control...the
other 10% is the PTO position. I do my best not to disturb the PTO shaft
but if you do that is pretty easy to fix too with a frequency counter. The
PTO tracks from 3.455 Mc to 2.455 on each band. It is inverse to the tuning
so it starts out on the high end and tracks to the low. So if you set up
the gear train after cleaning to the marks, reassemble the counter to the
front and set it to 2.000 Mc, have the timing marks on the band switch gears
back to their original position and the Xtal osc coupling adjusted to
indicate 2 Mc in it's window you can reinstall the RF deck. It's a little
tricky to hold everything in place as you remesh some of the chassis gearing
to the RF deck gearing but it can be done...without the "GREEN GEAR". If
you have it you can screw it in place after you set the gear train to the
marks and sync the counter to 2.000 Mc just to hold everything in place
while you set the RF deck back in place. A dab of heavy synthetic grease
will hold the Xtal switch Oldham coupler insert in place as you reassemble
the RF deck to the chassis. Leave the Oldham coupler insert out of the PTO
shaft coupling allowing easy adjustment of the PTO shaft position with your
fingers. At 2.000 Mc the output from the PTO should be near 3.455 Mc. Just
get it close so the couplers will align and reassemble the Oldham coupler.
Helps to have the screws on the PTO loose to do that.
With that your gear train is resync'ed.
At this point you go through the alignment which will include the fine
tuning of the PTO. The book covers all the rest!
Not a hard radio to work on. The IF is straight tuned...as opposed to the
stager tuning in the "A". The adjustment of the trimmers on the rear panel
can be a little tricky and if you get out of whack there the radio behaves
strangely but the procedure in the book works.
That's my experience with the R-390....in a nut shell.
I'd love to own an R-390 someday....all the ones that have passed through my
fingers have belonged to others. I really hated to see the last one go...it
was in such nice shape. Maybe someday....would be a nice companion to the
"A" and the SP-600 I think.
On another subject....I am in the process of finishing up the replacement of
the small coaxial cables on an R-390A RF deck...what a pain!
Cecil....
----- Original Message -----
From: "Barry Hauser" <barry at hausernet.com>
To: "Tom Norris" <r390radio at gmail.com>; <r-390 at mailman.qth.net>
Sent: Friday, December 16, 2005 8:15 AM
Subject: Re: [R-390] For the r-390 wishlist -- Things for the R-390/URR
> Hi Tom & Gang
>
> I have a few R-390's and R-391's. They all work - mostly. The only
> repair experience I've had was with one of the last R-390's out of Fair
> Radio. Dave, who used to work there back then and the R-390 resident
> expert, had kept it on his bench, tweaking it here and there and burning
> it in for a few weeks before shipping it. When I got it, it was DOA.
>
> The problem was an oddball one -- not dissimilar from your function switch
> experience on the R-390A. Someone mentioned some other situation that was
> similar - wire pinched by the IF deck or something like that.
>
> The R-390 has a big cable bundle running across the bottom of the
> mainframe. Where it crosses part of it is a cutout where there should be a
> small retainer clip. Sometimes they're missing. That cable bundle runs
> into a big connector that plugs into the audio deck. It's like the R-390A
> setup, only the R-390 has heavier coax. I'm not sure what made me do it,
> but I opened up that connector -- backed off the shell.
>
> Inside, the shield/braids of something like 12 or 13 cables are connected
> to a terminal in the connector by means of a piece of solid hookup wire.
> I seem to remember it was #13. May have some significance :-). The
> hookup wire and solder glob around it was cracked through from stress.
> Even with the shell off, it wasn't obvious.
>
> With or without that clip on the frame bottom, the cable bundle tends to
> sag and gets jostled when the receiver is set down or moved around. A
> bottom cover would minimize the movement, but still allow some jostling.
> While the bundle can shift, it's fairly stiff and puts quite a bit of
> stress on the connections inside the plug. Yes, there is a strain relief
> on it, but these are often not tight enough as the rubber wrap tends to
> shrink. Ground point for a lot of connections, so, if it fails it renders
> the rig inoperative. Short piece of hookup wire, soldering with a high
> wattage iron, shore up the strain relief and she's good to go. It's also
> a good idea to replace that clip and make things tight with some
> electrical tape or whatever.
>
> The only other things I know come from Dave Medley's notes -- like
> replacing the 47 ohm resistors, etc. -- and how to solid state the voltage
> regulator to eliminate the heat from the 6082's, though a muffin fan is
> another solution.
>
> I suspect many R-390's haven't needed the kind of intensive repair and
> pre-emptive PM applied to R-390A's, as they were of an earlier, more
> expensive, more proven design, and, as Les Locklear likes to quote, "a
> man's radio". That said, perhaps the most important tips are to 1. wear
> the correct (not politically correct) after shave, 2. but don't shave for
> a few days and work up a good sweat (so as to exude some manliness), 3.
> consume compatible beverages (like regular, like Southern Comfort, Jim
> Beam, etc., but not light beer or Tanqueray and so on. (If you go with 180
> proof rum, or vodka, you can also use it to clean the gear train -- and if
> you want to truly prove your manliness and bond with the radio, you can
> imbibe some of the gear train drippings). An ailing R-390 will generally
> perk up and work, purely out of mutual respect, even with a couple of weak
> tubes and crispened resistors.
>
> Don't know if all that really works, but does improve one's general
> orientation and attitude before approaching the project.
>
> Barry
>
>
> Tom wrote:
> Since Dave Medley retired, we've only see a few bits here and there on
> the R-390 vs the 390A. Anyone able to add any 390 experience?
>
> I've only recently dug into any R-390's. The 390A I can almost tear
> down and put together blindfolded* - though I'm not sure I can add
> anything that hasn't been covered in "Pearls"
> Other than the one odd troubleshooting incident written about earlier,
> I've not ran into many things that weren't simple by-the-book fixes.
>
> Reason I ask about the R-390 is I have 2 here that don't seem to have
> simple by-the-book problems. (they'll get back up on the bench
> eventually)
>
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