[R-390] HSR-2 vs 390a

Wed, 28 Jan 2004 19:48:28 -0600

Greetings all,

        Again I am a little late checking my mail today and this may have
already been addressed....

The issue in question here is the proper setting of the I.F. gain pot
internal to the radio.  Lots of folks believe that if there is a gain knob
higher has got to be better.  In actuality there is a setting for the I.F.
gain that is lower than the manufacturer published setting that results in
much improved overall sensitivity.

I have found the same to be true of other radio's...such as the R-1051
series.  I have found while experimenting with the alignment settings that a
decrease in I.F. gain in that radio would make the difference between a .5uv
10db over noise sensitivity and a better than 1.0uv 10db over noise
measurement.  The problem with the R-1051 was it's lack of audio
power...reducing the I.F. gain also reduced the resulting audio level but
greatly perked up the radio's sensitivity.  I have thought about finding out
how low results in a point of diminishing gains and just using an external
amp on the line out....I'll have to try that one day.

Best I remember from the old days ( a year or so ago) many of the guys were
running their R-390A's through one channel of their stereos by interfacing
to the diode load connections anyway....Sounds much much better...

This IF gain decrease also resulted in a lower internal noise level with the
RF gain full up.

I don't know about most of you guys but I run my RF gain full up most all
the time...of course with the AGC ON....

Hope that helps a little.

Cecil..
----- Original Message ----- 
From: "Dan Merz" <[email protected]>
To: "R-390 List" <[email protected]>
Sent: Wednesday, January 28, 2004 12:05 PM
Subject: Re: [R-390] HSR-2 vs 390a

> Hi again,  thanks for all the attention to my question regarding this
> homebrew receiver vs the 390a.  I have corresponded with the author a few
> times and see that his appreciation of the 390a is extensive and that he
> would never say his homebrew "runs circles"  around the 390a.  But on the
> other hand he has raised another question in my mind regarding the proper
> operation of a 390a.
>
> Keep in mind that I have a 390 i.f. chassis in my own set so my remarks
> concerning its operation are for that configuration at this point.
Putting
> the original chassis back in may be relatively simple but it's not
something
> I do casually or want to do very often,  even for comparison purposes.
But
> as I recall,  the other i.f. chassis did not operate much differently with
> respect to what I discuss below.
>
> So... the matter of hiss ,  as we call it,  came up.  This is the noise
that
> occurs when the r.f gain is turned up all the way with the antenna
> disconnected.  On my receiver (and the author's 390a which he no longer
> owns),  with the rf gain up all the way with the antenna disconnected,
> there is a noticeable hiss,  or background noise. The hiss is greater with
> the bfo on and increases in magnitude as the bandwith is switched to wider
> settings.  The hiss doen't move the S meter.  I took this as normal and
> typical of most radios.  It's not so loud that I considered it a problem
but
> maybe it is.   The author thought this was the thing about the 390a that
> interfered with reception of weak signals.  My question this time:  is
this
> a normal adjustment of the 390a and does this exist in your well-adjusted
> receiver?  I typically do not run the rf gain wide open because of this
and
> usually operate on ssb between 12  and 3 o'clock on the rf control.  I
think
> on strong AM stations,  the set works well with the rf gain wide open and
I
> never notice the hiss.    I performed the standard alignment procedures on
> my set awhile back but if this hiss is unusual I may start looking for a
> fix.     Dan.
>
>
>
> Dan Merz wrote:
>
> > Hi,  now I'm a relatively new guy on this reflector but I've gotten a
> > lot of good information out of the questions I've put on here - and I've
> > seen a lot of good information in the archives.  And I find the R390a I
> > have is the receiver I use most often,  pretty much standard except for
> > an audio improvement and substituting the 390 (non-a)  i.f. chassis.
> > So I'm putting a somewhat general query out based on a recent article I
> > read in Electric Radio,  Jan 2004 issue having to do with performance of
> > an apparently pretty simple homebrew receiver vs. R-390a.  Just for
> > information here,  the receiver consisted of 6be6 mxr, followed by 3
> > i.f.  6ba6 stages and 6bj6 det.  etc. with no rf tube in front of the
> > mxr,  just a couple of tuned circuits.  The full circuit is to come in a
> > future article.   What caught my attention was the statement -
> > "Comparison to my very well working 390a was dramatic,  I could CLEARLY
> > hear signals that were well under the hash level of the 390a, but very
> > comfortable copy on the homebrew receiver."  As best as I can tell,  the
> > radio is being used on 40 meters and frequencies below that and
> > primarily on AM.  I have in the past been made aware that rf stages in
> > front of the first mixer are not so necessary below 20 meters,  probably
> > first brought to my attention by the Squires-Sanders receivers and then
> > later by advanced transistor receivers in QST.  But what I'm wondering
> > about,  are there other factors that would make the 390a inferior in
> > certain cases to a simple receiver as expounded in this article?   Dan.
> >
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