[Hallicrafters] SX-42 alignment - msg. to Al Parker

[Al Parker]

Hi Skip et al,
    Ed brings up a good point, I had asked earlier abt the tuning cap &
dial, but where is the bandspread cap when you're aligning?   The SX-42's
has 2 sets of plates & is "half meshed" at the "rest" position.  After I
digest my supper I'll go down & look at mine so I can tell you which way it
oughta be.  I know I agonized a while before I decided mine was right.
    We'll get this thing licked eventually.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info

----- Original Message -----
From: <k6uuz at juno.com>
> I guess that you are ready to grasp at straws. Let me offer a few. I
> hesitated to jump in sooner as there are those smarter than me on the
> reflector and what I have to offer is pretty basic, but then, that is
> what gets us sometimes. I have aligned hundreds of radios and in so doing
> have come across some pretty weird things. Just recently I had one that
> would not calibrate, similar to your situation. The low end would come in
> but not the high end. What tipped me off was that 600 kc came in two
> places on the low end. Checking it physically found that the tuning cap
> was off about 30 degrees. so when tuning down it would close then start
> to open again. Setting it correctly corrected the problem and it aligned
> beautify.  Another case was where the kit builder set the tuning cap 180
> degrees off and crossed the dial cord to compensate. when applying a 600
> kc signal it appeared to come in at 600 kc as shown on the dial but was
> really the second harmonic of 1200 kc, as the tuning cap was nearly open.
> Setting it correctly cured that one too. If you have not already, check
> for physical problems. i.e. Tuning cap fully closed for the low end and
> opens correctly as you tune up. Some tuning caps are not symmetrical;
> that is the plates are not a true 1/2 circle but are cam shaped to try to
> make the dial more linear. Normally the low frequencies are stretched out
> and the high frequencies are crowded together. Most caps open from the
> bottom. Check that the dial cord is installed correctly. Check that the
> oscillator is on the correct side of the carrier. Probably higher than
> the carrier. You should find the carrier at two places on the dial; 2 X
> the I.F. frequency apart. For a 455 kc I.F. this is 910 kc. If you have
> high side injection, the lower one is correct. If low side injection, the
> upper one is correct. Select the correct one and tune the antenna, RF and
> mixer adjustments to peak on this one. The other one (the image) should
> be much weaker. All tuning adjustments should be near their center of
> range, that is in the middle 1/3 rd. The fact that your high end
> adjustments have small effect makes it suspicious that you have excess
> capacity, like the tuning cap nearly closed when it should be open. Good
> luck.
>
> Ed Richards K6UUZ
>
> On Sun, 27 Jul 2003 17:00:34 -0700 Waldo Magnuson <magnuson at mac.com>
> writes:
> > Hi Al,
> >     I'm rapidly getting totally frustrated with the SX-42 alignment.
> >     I first replaced C48 with a new silver mica of the same value
> > (470
> > pf).  No changes to speak of.  Both the old and new caps measured
> > about
> > the same value (I have a PACO and a Heathkit cap. tester and check
> > one
> > against the other).  I couldn't measure any leakage.
> >     I next substituted a 330 pf in place for C48.  I could still not
> >
> > tune to 1500 kc., 600 kc still tunes with the slug about 1 turn in.
> >
> > With the dial set at 1500 kc it takes an osc. setting of from 1200
> > to
> > 1380 kc to get any modulation output at the speaker terminals.  It's
> >
> > like C48 and C47 are being swamped by some other capacitance.  I
> > monitor osc. freq. with a HP freq. meter so I am confident of the
> > frequencies.
> >     I removed and inspected the slug of S-36 and it looks perfect.
> >     However someone (in the past) has replaced the cathode bypass
> > cap.
> > C38 with a 510 pf instead of a .01 uf.  It's tied to pin 4 of 7F8
> > mixer.  I don't see how this could change the tuning of T23 but I'll
> >
> > change it - very tough to get at.
> >     Al, I really appreciate your thinking about my 42 and the help.
> >
> > Thanks.
> > Skip Magnuson
> >
> > _______________________________________________
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> > dfischer at usol.com
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>
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