Good point on installing a fan to cool the high heat bottom of the R-390/URR.
Heat is the enemy of reliability.
Has anyone else noticed that the only difference between the R-390 and R-390A
power transformers is in the heater windings? The high voltage winding has the
same spec in both transformers. One could replace the regulated power supply
components and add a few 6H inductors, filter capacitors and eliminate some 50
watts of heat in the R-390/URR. The end result is that you will have the same
B+ ripple spec but have a somewhat looser B+ tolerance in the R-390/URR but
have the same as in the R-390A. With the modern AC line spec of +/- 5%, the
swing choke is overkill, IMHO.
Jim
Logic: Method used to arrive at the wrong conclusion, with confidence. Murphy
On Tuesday, August 12, 2025 at 11:57:27 AM CDT, Alex Hopper
<ahopper0...@gmail.com> wrote:
Hi Adam,
I recently had a R-390 restored by someone who has restored several of my
communications receivers. The receiver LOOKED OK, but many problems were
identified along the way. I needed to source a new crystal oscillator
module as the bandswitch in mine was junk. Additionally, one of the audio
filters (FL602 if I remember correctly) needed to be replaced, as well as
Z503 which is a small inductor on the IF module used in the AGC circuit.
When this was found to be failed (open), and while sourcing a replacement
for the gentleman restoring my set, I came to find out that Z503 is a
common point of failure on the R-390 and 390A. Beyond that I several
tubes were replaced as is common.
The power supply in my example had been (very poorly!) converted to solid
state. This supply was completely rebuilt, the diodes were removed and the
original rectifier tubes installed in their place. The regulated B+ reads
just about 185V at this point off the regulator tubes. I would strongly
advise installing some fans to help cool your receiver when you have it up
and functioning well. I placed my set in a Hammond steel cabinet with an
open back. I brought the cabinet to a local welding shop and they cut
holes in the top above the area that the IF module sits under, and on the
lower left side next to the regulator tubes. These both draw air out of
the receiver, and help keep the components in the IF module from cooking.
The man who restored the set also got a 5V tap off the transformer and
installed a small fan next to the rectifier tubes to blow air over them.
Good luck - would love to see photos of your new set!
-Alex
On Tue, Aug 12, 2025 at 12:33 PM Adam Morehouse <morehous...@gmail.com>
wrote:
> Thanks guys! When I get home tonight I'll yank out the PS. I did buy one of
> Tom Frobase's SS regulators, so I'll put that in when it arrives.
> During my quick glance, I noticed the big 10uF cap behind the front panel
> has a lot of crud around the terminals, so that'll probably have to go.
>
> The previous owner also gave me a Treetop circuits product detector, never
> installed. Not sure if I'll hook that up in the A or the Non-A just yet. I
> also have one of Tom's SSB / Sync detectors for my first 'A'.
>
> Adam
>
> On Tue, Aug 12, 2025 at 12:27 PM Renee K6FSB <k6fs...@gmail.com> wrote:
>
> > Hi Adam-
> > for the R390, IMO biggest issue is in the power supply, if Rick went
> > through it in ' 04 most likely good to go.
> > although best to pull pwr sply and have a look, heat is the issue
> > especially 47 ohm resistors. 6080s do get hot!
> > most everything else is pretty good as caps are Vitamin Q , selenium
> > rectifier may have been replaced., most of the time ok.
> > of course - filter caps..the usual applies...check them.
> > Renée
> >
> >
> > On 8/12/25 8:11 AM, Adam Morehouse wrote:
> >
> > Hey guys,
> >
> > Long time lurker here. You fellas helped me through my R-390A restoration
> > (which just got back from Bill Riches for his finishing touches). This
> > weekend I purchased an R-390, and another R-390A. Both them are are
> pretty
> > pristine - faces are great, extremely clean inside. The R390A has some
> > weirds to the IF deck and Audio deck, which I haven't figured out....the
> > R390 looks untouched.
> >
> > I am not very smart with electronics - I'm a young man, and typically
> > restore old Philcos, Zeniths, etc as a hobby. Replacing caps and
> resistors
> > I can do. Everything else confuses me, but I am trying to learn,
> especially
> > since I've got a growing collection of communication receivers.
> >
> > Supposedly, the R390 went to Rick Mish around 2004 - I think the owner
> > might be confused with the R-390A, as it's cleaner than new inside. The
> > R390 looks untouched. I am sad that there doesn't seem to be as many
> > articles, etc for the non-A...I do some original TM's on the way.
> >
> > In order to test thing, what are the bare minimum caps/resistors to
> > replace? I haven't torn it down yet - I see a 10uF can behind the front
> > cover, and what looks like an oil filled cap near the P/S. Hopefully
> > nothing under the RF deck needs to be looked at, as that seems like a
> bear
> > compared to the R390A.
> >
> >
> > Thanks for any help, or advice. I really appreciate it!
> >
> > Adam K2AAM
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