[R-390] R-390 Digest, Vol 83, Issue 19

[Tisha Hayes]

> ---------- Forwarded message ----------
> From: "Todd, KA1KAQ" <ka1kaq at gmail.com>
> To: "Michael, W1RC" <subs at w1rc.net>
> Date: Tue, 8 Mar 2011 11:45:29 -0500
> Subject: Re: [R-390] R390/URR manuals
> On Tue, Mar 8, 2011 at 8:49 AM, Michael, W1RC <subs at w1rc.net> wrote:
>
> > As timing would have it right now I am working on an R-390 and need
> > to know if anyone has the Field Change Orders.  Specifically I need
> > some information contained in both C1 and C3.  There is a "Zero
> > Adjustment" caution that I would like to see.  I am just about to
> > remove the front panel and there is a handwritten notation in my
> > TM11-5820-357-35 that I should see these items.
> >
> > If anyone has C1 and/or C3 would you be so kind as to post these
> > cautions.  I haven't played much with these radios for about 13 years
> > and I don't want to damage anything by virtue of forgetfulness.
>
> " In receivers modified by MWO 11-5820-294-35/1, the wires connected
> to B+ 3/8A Fuse F102 are removed and tied together, and the ground
> connection on transformer T801 is removed. There is no
> connection between the DC 20A Fuse F103 and P118-15 (not applicable to
> Fig 53 of TM), and Terminal 6 of T801 is connected through the contacts of
> J818-15 and P118-15 and B+ 3/8A Fuse F102 to ground.
> The B+ 3/8A Fuse is called the HV 3/8A Fuse.
>
> Power Supplies PP-621/URR modified in accordance with MWO
> 11-5820-294-35/1 are NOT interchangeable with power supplies that are not
> so marked because of wiring changes in the B+ 3/8A Fuse F102 circuit.
>
> R-390/URR Receivers modified by MWO -35/1 above have the former B+
> 3/8A Fuse F102 in the ground lead of power transformer T801 and the name of
> the fuse is changed to HV 3/8A.
>
> *Always a nice idea to put a fuse on the B+ so a bad cap does not roast a
> choke or the power transformer. Good idea to go through and look at those
> can electrolytics on the audio deck as well.
> *

 --------------------------------------------------------

> URGENT
> MWO 11-5820-294-35/2
>
> DEPARTMENT OF THE ARMY MODIFICATION WORK ORDER
> MODIFICATION OF RADIO RECEIVERS R-390/URR AND R-390A/URR TO ELIMINATE
> SPURIOUS RADIATION.
>
> *Not a bad idea, someone must have looked closely at the spurious
radiation and did not end up being a target for a soviet version of an
AGM-88 HARM missile. Easy mod to do, might even help you if your shack has
multiple receivers running at the same time. *
----------------------------------------------

> Micro Dial on BFO for ASA
>

*Sounds like a cool mod... wish they had came up with a retrofit kit to add
crystal controlled LSB/ USB/ DSB selection in addition to the BFO... Have an
interesting schematic and the right crystals... gives me ideas for a mod.

Of course it would make the TMC SSB adapter sort of redundant. Too bad
Collins did not jump on the SSB bandwagon back in the early 50's.
 *----------------------------------------------

> Re-cabling the antenna relay to use the C connector
>

*Probably overlooked by many users. If you follow the schematic for the
balanced and unbalanced whip antenna connections you can see where a swap of
the BNC connections on the bottom of the antenna relay would be a good idea.
You do not even need to heat up a soldering iron for this mod.*
------------------------------------------------

> Diode mod to replace the 26Z5's.
>

*Just remember what happens to the B+ with a solid stated replacement of the
26Z5 tubes. You probably do not want to leave the radio in the standby mode
unless you like to stress test the B+ caps and a bunch of tubes with high B+
voltages.  Had an idea to use a MOV and load resistor to limit the B+
excursions with a shunt type regulator.*

Ms. Tisha Hayes/ AA4HA
----------------
"I'll be a diode, cathode, electrode
Overload, generator, oscillator
Make a circuit with me." -- The Polecats