[Hallicrafters] SX-24 Questions

[Mike Everette]

The SX-24 schematic and alignment info from the Riders
manual is available on line at www.nostalgiaair.org

Click on "Resources" and then scroll down to
Hallicrafters.  The file is 2 or 3 pages in pdf
format.

The complete SX-24 manual is available at
http://bama.sbc.edu but it is a djvu file which
Internet Explorer does not like.  If you use Netscape
or Mozilla Firefox as a browser you can probably
download it with no problem.    You can also get it
from the e-debris web site, and there is a link to
this at the top of the BAMA home page.

The major differences between the SX-24 and SX-25 are
that the 24 has only one tuned RF stage, but the 25
has 2.  The 24 has single-ended audio output while the
25 is push-pull, and also has a phase inverter tube to
drive the push pull output.  The 24 uses a 76 tube as
the BFO, the 25 uses a 6J5.  Other than other minor
differences, they are very much alike.

If you are finding the resistors to be within 5% you
are very, very lucky; or as you say, someone may have
had a resistor-party years back.  The original ones
are not very high quality.  My normal policy is to
replace any that are much more than 10% off, even
though they were originally 20% tolerance.

Just about all the ones in my 25 were at least 40% off
and many were 80% to 100%.  It seems that the higher
the marked value, the morelikely they are to age
higher.  I even found one large 15K high wattage
carbon resistor in the power supply voltage divider
that had gone up to 23K.  The 25 is not the only
receiver in which I have encountered this; also two
S-20Rs, an S-22R, S-27 and SX-28 of this similar
vintage (the 28 gets ALL new resistors as it is too
much trouble to go back and change one!); I also have
a 24 awaiting a turn on the bench and fully expect it
to be like the others with regard to resistors.  I
have also encountered this in more recent Hallis such
as the S-40, S-76 and later, but not to such an
extent.

Be sure you're reading those color codes correctly...
if there is doubt, nostalgiaair also has a guide to
vintage color codes on the site.

Darryl, if you like, I can make a copy of the info I
have on the SX-24 and mail it to you, if you send me
your address off list.

The advice you got about aligning the IF to the exact
crystal filter peak frequency is quite correct of
course; but if you switch to any of the non-crystal
positions and just try peaking up the IF trimmers,
this will tell you if some whiz-bang's dirty hands and
tools have been where they shouldn't be.  You'll want
to do a complete re-alignment anyway, once the
recapping and re-resistoring are done.

73

Mike
WA4DLF



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