[R-390] R390A to R725 conversion question

[Tom M.]

There was a guy who told me used the ovens power to run a R390 if deck and kept the ovens off. I have not verified that it’s plausible but he said he did it. Might be worth a look. 


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On Thursday, October 31, 2024, 3:32 AM, Larry Haney <larry41gm2 at gmail.com> wrote:

Hi All,  Tom Marcotte made a nice post on this subject on  Sun, 21 Aug 2005 16:14:25 -0700 (PDT).  It's in the Pearls 'IF_Deck' section and titled 'R-725, How To Make Your Own'.  This would  be a good place to start and there are many other posts in there on this subject, also.
Perhaps a document on this subject would be beneficial to put on our website, if someone would put one together.
Tom, 
You had a number of links in your R-725 posts referencing 'geocities,com', but those seem to be gone now.  Do you still have them somewhere?  Thanks.
Regards, Larry



On Wed, Oct 30, 2024 at 5:38 PM Tom M. via R-390 <r-390 at mailman.qth.net> wrote:

 Perry,
The added transformer in the R-725 was for PTO hum bucking, not filaments. sk Wally Chambers informed me of that fact.

The R-725 had the rewired R-390 filaments.  I've done this myself and wrote a procedure how to do it. I agree with you it was a bit of a PITA.
I use the converted IF deck in my daily driver R-390A to this day.
Tom




    On Wednesday, October 30, 2024 at 04:31:35 PM CDT, Perry Sandeen via R-390 <r-390 at mailman.qth.net> wrote:  

 List,
IIRC I've seen 3 published articles for r390a to r725 conversion all using the re-wiring of the R390 IF to 6 volt filaments.  This seems to be a big PITA.
When the military did the original they just added another 26 volt filament xformer. This seems a much easier approach especially when we have small SRPS's available.

If anyone would have the schematics or TM addendum I would appreciate it if they would contact me off list.
TIA
Perry
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