[ARC5] Using SCR-274N (Very brief comment from Les)

Sun Mar 31 17:38:46 EDT 2013

  Adding nothing, I find these "Saturday night thoughts" very
  interesting.

73 de Les Smith
  vk2bcu at operamail.com

On Mon, Apr 1, 2013, at 1:23, Bill Cromwell wrote:
> On Sat, 2013-03-30 at 20:11 -0700, Mike Everette wrote:
> > Perhaps the point has already been made, perhaps done to death... but,
> >  to my way of thinking, the ultimate SCR-274N/ARC-5 receiver setup is
> >  the "ARC-5 Triple Superhet" idea published in QST in the late 50s. 
> >  This yields a triple conversion receiver, by combining one of the HF
> >  receivers which has been stripped down and its BFO made into a second
> >  conversion oscillator to take the IF of the high freq receiver down to
> >  455 kc to feed into a BC-453 or R-23/ARC-5.
> 
> Hi Mike,
> 
> I thought about doing something like that, too. To do it will require
> some expense in cash (probably not a lot) and quite a bit of effort (but
> it's a hobby). Better performance is had with *ANY* receiver if the main
> selectivity is closer to the antenna as opposed to being at the end of
> the last IF or even at the end of the audio output. That makes less
> difference for casual operation. It also is less of a problem if the
> front end is less susceptible to overload. Using "ARC-5" command
> receivers *as-is* it's easy enough to avoid overload due to the way the
> gain control controls. You just have to be a radio operator - not an
> unpleasant proposition. I think the effort should be put into something
> a little more productive and a little less destructive.
> 
> > 
> > This yields an excellent receiver.  I built one once (then, like an
> >  idiot, sold it at a hamfest), and can testify to its many merits.  It
> >  runs rings around Ikensu junk of today, and would give many
> >  sophisticated vintage receivers a run for the money.
> 
> I have read testimony from a couple of hams who let those go and
> regretted it.
> 
> > 
> > Such an approach avoids miscegenating an SCR-274N or ARC-5 receiver
> >  with solid state thingies (I would say JUNK, but some might not like
> >  that... hmm, I don't think I care....)
> 
> If you don't mind the extra drain on the power budget a lot of outboard
> accessories can be used to help sort signals built around tubes. You
> could even use a passive audio filter in the low level audio stages
> (ahead of that single ARC-5 audio tube) for some help. No active devices
> at all. The RAK/RAL do that quite effectively (but they do have some
> loss). And there are quite a few ways to use something like a
> "Select-O-Ject" and other vacuum tube processing to reduce otherwise
> unmanageable QRM. I'm not sure if a SCAF filter would be practical in
> hollow state. It's somewhat more sophisticated than the select-o-ject
> (but duplicates it) and not as complicated as a full blown DSP unit.
> Adding a xtal filter at the original IF frequency seems a lot more
> desirable than making virtually irreversible mods to a receiver that
> already does a pretty good job "as-is". With those bathtub caps gone
> (replaced with new caps) there is room for an xtal filter module under
> the chassis.
> 
> > 
> > But as for "Using SCR-274N," even AS THEY COME, they are VERY usable.  
> > 
> > I'd like to point out that back in the day, a lot of us used what we
> >  could get our hands on CHEAP.  Many Novices cut their teeth on Command
> >  Set receivers which they got for anywhere from free to $5 or $10, with
> >  no added IF filtering or other stuff.  And, the darn things will hear
> >  any signal on the air, be it emanating from Outer Mongolia, B-F-E, or
> >  wherever.
> 
> I remember 'back in the day'. $5 or $10 was about what I earned working
> in people's yards or shoveling snow for two or even three weeks. And
> um... how many kilowatt stations were transmitting in the novice band to
> overload those receivers? My 40 meter receiver arrived already recapped
> and ready to rock n roll. It has the widest IF channel of all of my
> receivers even my regens! I applied an antenna and power before I even
> picked up the spilled foam peanuts from the floor. No problem copying
> any one of a dozen signals that were present in the passband. It just
> sounded different than my Ten Tec or Kenwood with the wide filters
> selected. The scaf filter plugged in where the cans plug into the radio
> turned it right into Cadillac! Maybe it would be back to Ford Pinto
> status in the sweeps...maybe not. They really are "very usable".
> 
> >   
> > 
> > Granted, you may hear a lot of other signals in the passband; but
> >  that's where SKILL comes into play.  The human brain is by far a
> >  better selective filter than anything else, if properly trained.  It
> >  may come as a surprise to many in today's plug-n-play, computer
> >  (de)generated world that this is still a basic truth. 
> 
> Each of us have a completely unique hearing response (as with all of our
> other responses). Most of us can do that to one degree or other. Many of
> us could do it quite well. For me it's like being in a busy, popular
> restaurant surrounded by many conversations. We listen to one of
> interest (probably our lady friend or XYL) and ignore the rest. However,
> if a loud fight breaks out at the other end of the place or the music is
> too *LOUD* it gets more difficult and we throw in the towel. Most of the
> time band conditions on 80 and 40 meters are just not that crowded. I
> think back in the day more transmitters had there own "character' and
> that helped too. In that crowded restaurant your lady's voice has it's
> own sound and that helps. Today most of the rigs on the air sound
> exactly the same and when computers send the CW there isn't even an
> accent from the fist!
> 
> >  
> > 
> > Even a barn-door, four-track-railroad-wide Command Set receiver still
> >  beats stuff like the Hallicrafters S-38 from back in the day.
> > 
> > But that ARC-5 Triple Superhet will slice signals thinner than Pringles
> >  potato chips.... ga-ron-teed.
> > 
> 
> The measured specs tell us the R-23/BC-453 can be choked down to about 1
> kc wide at the peak and 2 or 3 kc further down the slope where more
> doesn't matter as much. That's a whole lot better than 15kc!! or the
> entire novice band at once (grin).
> 
> 
> > If I have time to get it going I may just build up one of these
> >  receivers and take it on Field Day this year.  Gaaa-aaaaAAAAAAh-LEEE!
> > 
> > For whatever these late-Saturday-night thoughts may be worth....
> > 
> 
> They're worth a lot. It pays to review the basics from time to time and
> those radios will force us to do that.
> 
> 
> > 73
> > 
> > Mike
> > W4DSE
> 
> 
> 73,
> 
> Bill  KU8H
> 
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