[R-390] service of an R-725

[Tom M.]

R-725s were actually modified R-390As.
Prototyped by Motorola, and then modified by Servo and Arvin, they installed new purpose built IF decks (essentially R-390 IF decks) and a hum bucking transformer for the PTO, also a shield for the PTO.
One can actually rewire a R-390 IF deck and install it in a R-390A.  I did this and wrote a procedure for it.
The R-725 is a nice radio.  You can get the same sound from a R-390.
Tom N5OFF




      From: Bill Riches <bill.riches at verizon.net>
 To: wb3fau55 at neo.rr.com; r-390 at mailman.qth.net 
 Sent: Monday, December 5, 2016 7:25 PM
 Subject: Re: [R-390] service of an R-725
   
I have an R-725 - it is an R390a with an R390 if deck.  Seems that for
diversity DF work the R390a mech filters caused errors in readings.  Servo
company modified R390A by putting in R390 if decks and added a separate fil
transformer for the PTO which is different than the R390A one.  Great
receiver - I think only about a thousand of them were made as compared to
the gazillion of our R390a receivers.  Out of over a hundred R390a receivers
that I have restored, I have only done two of the R725s.  Only difference
you will probably notice is that the audio sounds cleaner.  Selectivity
shape is very close to the mechanical filter shape.  Maybe an Idea to hoard
some R390 if modules for when there are no more good mech filters!

73,

Bill, WA2DVU
Cape May

-----Original Message-----
From: R-390 [mailto:r-390-bounces at mailman.qth.net] On Behalf Of
wb3fau55 at neo.rr.com
Sent: Monday, December 5, 2016 7:08 PM
To: r-390 at mailman.qth.net
Subject: [R-390] service of an R-725

390A gurus-  a number of questions concerning the R-725.  So straighten me
on a number of points with  this item.  A 725 is a modified 390A,  not using
mech. filters,  for whatever reason?  
 I may get one of these for repair.  The problem- no receive below 8mc.
Fairly common problem in the 390A,  in the 1st xtal osc.  So my main
question is-  any difference in the RF deck of a 725 vs. a 390A?
 As alaways, thanks for your input-73s Russ.
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