[R-390] HSR-2 vs 390a

[Dan Merz]

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.
>
> _______________________________________________
> R-390 mailing list
> R-390@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/r-390