[R-390] RE: HSR-2 vs 390a

[Cecil Acuff]

Those sound like some good ideas to check out...I had thought about the IF
deck mod to replace the Mechanicals with some LC filtering or ceramics.  I
know many new radio's now days can be ordered with the Collins mechanicals
or ceramic filters so there must be some level of interchangeability.

Good thoughts...

Cecil...
----- Original Message ----- 
From: "Drew Papanek" <drewmaster813@hotmail.com>
To: <r-390@mailman.qth.net>
Sent: Tuesday, January 27, 2004 5:13 PM
Subject: [R-390] RE: HSR-2 vs 390a


>
> On an Electric Radio article comparing the simple HSR-2 vs the R-390a, Dan
> Merz wrote:
>
>
> 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."
>
> (snipped)
>
> 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?
>
> The aforementioned statement regarding HASH level of the R-390A could have
> some basis even for a well-functioning R-390A.
>
> The R-390A's mechanical filter response has extremely sharp skirts;
> wonderful in crowded ham band conditions but not so good in impulse noise
> situations.
>
> Hash as we sometimes define it is a form of impulse noise. Those filters
> will ping and ring, "smearing" out the pulses and making interference
worse.
>   One listening to a high quality AM signal with the R-390A can hear a
> slight raspiness to the audio; the filters ring on transient modulation
> peaks.
>
> The R-390 non-A has LC filtering (the IF cans) which has a more gradual
> skirt characteristic largely devoid of ringing and hence does far better
in
> the presence of impulse noise.  That also accounts for the superior audio
> quality of the non-A.
>
> I have an el cheapo Hallicrafters S-120 which is a low entry level general
> coverage receiver.  Tube lineup is the All-American Five minus the 35W4
> (selenium instead).  Normally in side by side comparisons a signal that is
> not even detectable on the Halli will be armchair copy on my R-390A. But
> enter strong 60 Hz power line hash and on moderate strength signals the
> great '390A is humbled by the lowly Halli.
>
> Rolling your own R-725 by stuffing the non-A IF module into an R-390A has
> its merits.  However, that module can be hard to come by.
>
> Here are some ideas (possibly without merit) I've been pondering for
R-390A
> IF module modification.
>
> (Forum Tranquility Preservation Statement: Performing the following
> modifications would constitute heresy!  Shame upon he who would attempt
> them!)
>
> 1.Replace one or more of the "mechanism a philharmonic" (mechanical
filters)
> with a filter comprising cascaded LC sections. These could be modern
> miniature IF cans with added impedance matching in and out.  Modern
ceramic
> filters plus impedance matching schemes could also be used.
>
>
> 2.Bypass 16 KHz filter entirely, add attenuation to match losses in the
> remaining filters.  Change values of or  remove the Q spoiler resistors in
> the R-390A's IF cans.  Realign with less (or even no) frequency
staggering.
> Fiddle with cathode resistors to reduce the gain which was raised by can
> mods. The IF cans so adjusted would then define bandwidth in the switch
> position labeled "16 Kc".  That would be the high fidelity, impulse noise
> resistant mode.
>
> Using the narrower bandwidth positions would then provide mechanical
> filtration at the original bandwidths (provided the filter in use had a
> narrower bandwidth than newly defined by IF cans). Original function (and
> susceptibility to impulse noise) in the narrower positions would be
> preserved.
>
> These modifications might be attractive to one whose IF module has a
defunct
> 16 KHz filter, if not for the fact that the 4Khz filter fails most
> frequently.
>
> 3. Keep the Philharmonic Quartet (16, 8, 4 ,2 Khz) intact but add relay
> switching to put the Quartet on hold and swap in LC or ceramic filtration
as
> desired.
>
> 4. Add that panadaptor output jack you've been thinking about and use it
to
> feed an external IF/detector/audio unit.
>
> A better "modification" might be to acquire the R-390 non-A.
>
> Drew
>
> "Vicariously repairing and defiling R-390x via advice to others"
>
> _________________________________________________________________
> Rethink your business approach for the new year with the helpful tips
here.
> http://special.msn.com/bcentral/prep04.armx
>
> _______________________________________________
> R-390 mailing list
> R-390@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/r-390