Fw: [R-390]

[Michael Murphy]

The values in the text of article will give you a little more than a Watt on
the internal R390A iron or with a small All american 5 transformer.

The actual "final" schematic shown is for the larger transformer from AES. I
did not get data on this to ER in time for publication.  Note that the
cathode resistor is 220 Ohms (lower that the value in the article); anyway I
got 2.4 Watts out with the larger transformer. Also note that I threw in
some feedback around the transformer in addition to the primary side
feedback which was retained.

Mike WB2UID
----- Original Message -----
From: "Dan Merz" <djmerz at 3-cities.com>
To: "Lee Bahr" <pulsarxp at earthlink.net>; "R-390 List"
<r-390 at mailman.qth.net>
Sent: Sunday, June 20, 2004 11:18 PM
Subject: Re: Fw: [R-390]


> Lee,  I haven't tried the 6aq5 audio mod in the recent ER but it looks
> interesting and should be an improvement.  I completed the earlier mod
mentioned
> in the article which put a push-pull 6360 tube (twin tetrode)  as output
tube in
> place of one of the tubes,  also an ER article.  This was somewhat more
> complicated and works very well and is less likely to saturate the core of
the
> small audio transformer that can fit on the chassis.  I was a little
surprised
> the recent author didn't do some sort of comparison or even mention why he
> didn't go with the earlier 6360 mod,  but I'm guessing it was because his
mod is
> easier to do (doesn't require changing a tube socket).  His article did
have the
> word SIMPLE in the title !!  And maybe he thought a 6aq5 should be used
because
> after all it's an audio tube whereas a 6360 is a vhf transmitter tube.   I
> bought a second audio chassis for the mod but I haven't put my original
chassis
> back in since - the audio is very good.  Maybe the next owner will want
the
> original so that is why I kept the chassis I got with the set in its
original
> state.  best regards,   Dan
>
> Lee Bahr wrote:
>
> > I went to the Arlington Ham Comm in Texas yesterday and bought my third
> > R-390A.  It was a Motorola, serial # 1587.  All meters are intact but
the
> > chap who sold it to me for $250 said it does not work on all bands and
he
> > didn't  know what was wrong with it. He said he found it in a
corporation's
> > disposable pile.  Now I have 3 of them to restore!  (The other two are
EAS
> > units).  The Motorola unit looks clean and the front panel is nice but
not
> > perfect.  All the covers are there.
> >
> > What would be the most logical reason for some bands not working?  I
guess
> > crystals would be suspect and maybe switch contacts, if nobody was
screwing
> > slugs around in the unit.  (I'll check to see if rack coil slugs are
> > moving).
> >
> > Also, what do you guys think of the latest Electric Radio's article
(June,
> > 2004) on improving R-390A audio?  I'm thinking of trying this if I
ever/when
> > get my radios up and running,
> >
> > I just ordered the two sets of Hi-Res videos on the R-390A as well as
the
> > set for the SP-600JX but they have not arrived from Hi-Res as yet.  My
two
> > cap kits for my first two R390As have been sitting on the work bench for
> > weeks now.  Maybe the videos will get me going!
> >
> > Lee, w0vt
> > Houston
> >
> > _______________________________________________
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> > http://mailman.qth.net/mailman/listinfo/r-390
>
>
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