[R-390] 390 non-a i.f. in R390a
Tom M.
[email protected]
Mon, 20 Jan 2003 14:31:42 -0800 (PST)
Scott,
The R-725/URR is a modified variant of the R-390A. It has a special IF deck
(95% like the R-390 IF deck except it runs on 6V instead of 24V)called the
Series 500 deck, which enables the 390A frame to be used in DF applications as
with the TRD-15. The R-725 also has a PTO mod to prevent hum.
Motorola, Arvin and Servo were engaged in making the new IF decks for dropping
into existing R-390A's, pressing them into DF service. The new IF decks were
not entirely new; some parts were salvaged from the (now junker) R-390A IF
decks that were removed.
The R-725 has the nice sound provided by the tuned circuit IF, arguably better
than that of the 390A with mechanical filters.
Why not use the 390? Because I don't have one. The objective of the project
was to get better sound out of the R-390A, keeping the R-390A IF deck availble
for hard core DX. There are no permanent mods to the 390A, which was another
objective.
73!
Tom N5OFF
--- Scott Seickel <[email protected]> wrote:
>
>
> Hi Dan,
> I do not receive Electric Radio and have no idea what a R-725 is.
> Would you be so kind as to clue me in?
> Did you do it for the fun of the project or is there some performance
> advantage that I am missing? I would imagine that it would make the
> radio better for SWL'ing but why not just use a 390?
>
> Thanks,
> Scott
>
>
>
>
>
>
> ----- Original Message -----
> From: "Dan Merz" <[email protected]>
> To: "R-390 List" <[email protected]>
> Sent: Monday, January 20, 2003 9:59 AM
> Subject: [R-390] 390 non-a i.f. in R390a
>
>
> > Hi, I completed the conversion of a 390 non-a i.f. chassis to go in a
> > R390a radio. This follows the article of Tom Marcotte in Electric Radio
> > Dec 2000 describing the conversion. I found his article flawless in the
> > detail given for point-by-point wiring changes and thank Tom for writing
> > the article and providing me a readable schematic for the 390 non-a
> > chassis and some other information on the R-725. I deviated slightly in
> > a couple of cases to utilize some of the existing wiring but this was
> > just a preference on my part and amounted to the same connections. Most
> > of the wiring mod's involve converting the series connections for 25 v
> > filament supply used in the 390 non-a to the 6.3 volt connections
> > required in the 390a, plus dropping the B+ voltage a bit. This is all
> > explained clearly in his article, along with the background for the
> > R-725 radio which the final set emulates. No modification of other
> > parts of the 390a radio are required other than taking the 390a i.f.
> > chassis out. The conversion was done on a junker 390 non-a i.f.
> > chassis sold on eBay and it worked immediately upon putting it into the
> > EAC 390a set, which brought a feeling of relief since I had no idea
> > what might be wrong with the junker chassis and I didn't have a 390
> > non-a radio to test it in. One of the bigger tasks was to make a cable
> > adapter for BNC to mini-BNC, or MB, connectors for the two inputs from
> > the 390a r.f. chassis. Tom used two of the 390a i.f. output adapters of
> > the type on the rear panel of a 390a. I had trouble finding these, and
> > I'd like to thank Roy Morgan for his assistance in trying to get the
> > relevant connectors from The RF Connection - I opted not to use their
> > MB female to BNC female adapter because the two critical parts would
> > have cost $20 each plus shipping and I would have to make up two short
> > BNC to BNC cables as well. Instead I used some chassis mount MB
> > connectors from Fair and made a small aluminum box with the MB
> > connectors on one side with RG 58 entering on the opposite side, with a
> > BNC connector on the outside end of the RG 58. I can't say cheaper is
> > better but it was a bit of fun and turned out well. If there is any
> > interest, I'll post the details of how I did that but it's not too
> > complicated. I'd recommend buying the RF Connection adapters unless you
> > enjoy cutting and bending metal like I do. I'm assuming the adapters
> > from RF C look more or less like the 390a back panel i.f. adapter.
> >
> > I was quite impressed with the appearance of the 390 i.f chassis,
> > though it's much more crowded than the 390a i.f. chassis and not the
> > easiest thing to reach into with a soldering iron, even a small one. My
> > first reaction on looking at what had to be done was "ughh." As Tom
> > advised, use any trick you can think of to do the soldering. So when I
> > finished the soldering, I felt I had done something challenging and had
> > not destroyed the beauty and function of the unit in the process. I
> > hope the next guy looking at it will find equal enjoyment with the
> > unit. This project took about 2 years to complete, most of that time
> > looking for the i.f. chassis after I read Tom's article. I got this
> > chassis Dec 27 so it took about 3 weeks to round up the connector stuff
> > and make the conversion after that.
> >
> > I'll post my impressions once I test the set a bit more; I'm going to
> > add the two diodes ala Lankford and increase the bfo coupling cap.
> > Thanks to all for earlier comments regarding the connectors, Dan
> >
> >
> > _______________________________________________
> > R-390 mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/r-390
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