[Hallicrafters] SX-28 Alignment instructions?

[Bill Feldmann]

Hi David,
That was a big mistake in step 5, C55 was a mistake. C65 will work fine
however I really measured across C66 where there was more voltage but C65
will work fine.  Also something was wrong in the formatting of the document,
a page break was added putting step 5 on a separate page.

Remove the page break after step 4 and change C55 to C66 in step 5.

Sorry I wrote it late at night and was a little punchy.

Bill

----- Original Message ----- 
From: "David Woodhead" <km5tz at san.rr.com>
To: "Bill Feldmann" <n6py at qnet.com>
Sent: Wednesday, October 27, 2004 7:02 PM
Subject: Re: [Hallicrafters] SX-28 Alignment instructions?


> Bill,
>
> I did some work on my SX-28 last night. Your instructions were great!
Check
> C55 on page 4 - I think it should be C65.
>
> I used a sweep generator to tune the IF - makes it easy.
>
> My crystal 452.5KHz.
>
> A little over 2 dB difference between IF broad and medium/narrow sttings.
>
> The difference between med and narrow bandwidths is a bit dissapointing -
> without your notes I would have susspected something was wrong!
>
> I could not get the AVC tansformer to peak so need to look into that...
>
> David.
>
> ----- Original Message ----- 
> From: "Bill Feldmann" <n6py at qnet.com>
> To: "David Woodhead" <km5tz at san.rr.com>
> Sent: Tuesday, October 26, 2004 7:28 AM
> Subject: Re: [Hallicrafters] SX-28 Alignment instructions?
>
>
> > Very slight difference, about 2db after it's properly aligned.
> >
> > Bill
> >
> > ----- Original Message ----- 
> > From: "David Woodhead" <km5tz at san.rr.com>
> > To: "Bill Feldmann" <n6py at qnet.com>
> > Sent: Monday, October 25, 2004 10:01 PM
> > Subject: Re: [Hallicrafters] SX-28 Alignment instructions?
> >
> >
> > > Quick question Bill - Do you see a significant difference in signal
> level
> > > between the 3 broad selectivity settings?
> > >
> > > What amplitude is you sig gen for the given AVC readings? This might
> help
> > > others quickly determine if they have a problem.
> > >
> > > David.
> > > ----- Original Message ----- 
> > > From: "Bill Feldmann" <n6py at qnet.com>
> > > To: "Brian NI6Q/F5VQ" <NI6Q at aol.com>; "David Woodhead"
> <km5tz at san.rr.com>
> > > Sent: Monday, October 25, 2004 9:30 PM
> > > Subject: Re: [Hallicrafters] SX-28 Alignment instructions?
> > >
> > >
> > > > Hi David and Brian,
> > > >
> > > > You question David came at the right time because I was having a fit
> > > trying
> > > > to align my second SX-28.  I thought I had a problem with the second
> IF
> > > > transformer, T2, because of the wide bandpass having a big hump on
its
> > low
> > > > end after following their procedure in the manual.
> > > >
> > > > After a day of troubleshooting today I found the problem.  Evidently
> the
> > > > first AVC transformer, T6, and the AVC amp were resonating around
> 448kc
> > if
> > > I
> > > > tuned T6 to 452kc, the same frequency as my crystal filter.  When I
> > tuned
> > > it
> > > > to exactly 455kc the problem went away.  I didn't have this problem
> with
> > > my
> > > > first and earlier design SX-28 so it was a little hard to
understand.
> > > This
> > > > resonance or feed through is most likely a problem with poor
shielding
> > of
> > > > the IF from the AVC circuit.
> > > >
> > > > I wrote up the attached procedure as a Word document to document the
> > best
> > > > way I found for alignment of the SX-28 IF.  I also found the
procedure
> > in
> > > > the manual very confusing, especially how to align the top slug of
T2
> > for
> > > > best filter notch.  But I think I figured out what they wanted to
say,
> > get
> > > a
> > > > good dip between two peaks while adjusting the top slug or secondary
> of
> > > T2.
> > > > Also by writing it down I have it to use in the future or any ER
> article
> > I
> > > > write on my experience with the SX-28.
> > > >
> > > > I find it's best to do a rough alignment at 455kc with the first AVC
> > > detuned
> > > > to prevent any interaction with the IF alignment, then find the
> crystal
> > > > frequency, and then re-align the IF to that frequency.  Finally to
> align
> > > the
> > > > crystal filter followed by peaking T6 for the first AVC at a little
> > above
> > > > the crystal frequency which seemed to stop the feed through or
> resonance
> > > > problem in my second SX-28.
> > > >
> > > > In the attached procedure I mention the band widths I came up with
> after
> > > > alignment of my SX-28's.  The later one is a little wider in the mid
> and
> > > > sharp non-crystal settings than the early one.  It may be a design
> > change
> > > > since the transformers look a little different between the two.
> > > >
> > > > I also sent this to you Brian because you are most likely trying to
> > figure
> > > > out this confusing procedure and my run into this T6 resonance
> problem.
> > > >
> > > > Bill N6PY
> > > >
> > > > ----- Original Message ----- 
> > > > From: "David Woodhead" <km5tz at san.rr.com>
> > > > To: <Hallicrafters at mailman.qth.net>
> > > > Sent: Sunday, October 24, 2004 4:06 PM
> > > > Subject: [Hallicrafters] SX-28 Alignment instructions?
> > > >
> > > >
> > > > > Does anyone have any decent alignment instructions for the SX-28
IF
> > > stages
> > > > (especially the crystal filter + IF BW adjustments)? The manual
> > > instructions
> > > > seem very poor to me.
> > > > >
> > > > > When switching between the 3 broad bandwidth settings (no xtal),
how
> > > much
> > > > variation do you see in signal level?
> > > > >
> > > > > Thanks!
> > > > > David
> > > > > KM5TZ
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> >