[R-390] 390 non-a i.f. in R390a

[Scott Seickel]

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" <djmerz@3-cities.com>
To: "R-390 List" <r-390@mailman.qth.net>
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
> 
> 
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