Tricks for aligning Hallicrafters SX-28?
 

I was tearing out my hair trying to align my SX-28's IFs at 455 kc when I
remembered this note in my old SX-28 notebook from about six years ago:

"Be aware that the crystal filter alignment instructions are wholly
incomprehensible. Bottom line is you do a rough IF alignment to 455 Khz
(bandpass set to IF narrow). Then you center the phasing cap and switch to
crystal sharp. Crank up your generator and try to find the center of the
crystal frequency. It's not easy, VERY twitchy, since the bandpass is about
100 Hz. Once you have the generator centered dead bang on the crystal, don't
touch it and go back and tweak the IF alignment on that frequency (at IF
narrow bandwidth). A counter helps."

I believe the note came from A.B. Bonds. In any case, once I followed this
advice, my squealing monster aligned on the IF just fine. According to my
frequency counter, the magic number for my set is 456.9, not 455.0.

Any other useful tricks to know? I tried aligning the AVC by the book, but
didn't get good results. The AVC actually seems to work better when I set it
by ear, although I'm sure that sends a thrill of horror down the back of a
serious restorer.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

On 7-Mar-2005, "Phil Nelson" belted out:

I was tearing out my hair trying to align my SX-28's IFs at 455 kc when I
remembered this note in my old SX-28 notebook from about six years ago:

"Be aware that the crystal filter alignment instructions are wholly
incomprehensible. Bottom line is you do a rough IF alignment to 455 Khz
(bandpass set to IF narrow). Then you center the phasing cap and switch to

crystal sharp. Crank up your generator and try to find the center of the
crystal frequency. It's not easy, VERY twitchy, since the bandpass is
about
100 Hz. Once you have the generator centered dead bang on the crystal,
don't
touch it and go back and tweak the IF alignment on that frequency (at IF
narrow bandwidth). A counter helps."

Here is a classic example of "The Old Ways Are Sometimes Best." I have a
synthesized signal generator which I love dearly. If I had had it in 'Nam,
we would have won. Be that as it may, it is virtually useless for this
application because the exact crystal frequency always falls between two of
the steps. I don't have that problem with the URM-25.

Did you ever find a meter Phil?

Nope, still lookin'.

Phil

Thanks for reminding me why I sold off my SX-28A about two years ago.

Kenwoods and Icoms for me now.....and I don't need a toupee.



"Phil Nelson" wrote in message
ink.net...
I was tearing out my hair trying to align my SX-28's IFs at 455 kc when I
remembered this note in my old SX-28 notebook from about six years ago:

"Be aware that the crystal filter alignment instructions are wholly
incomprehensible. Bottom line is you do a rough IF alignment to 455 Khz
(bandpass set to IF narrow). Then you center the phasing cap and switch to
crystal sharp. Crank up your generator and try to find the center of the
crystal frequency. It's not easy, VERY twitchy, since the bandpass is
about 100 Hz. Once you have the generator centered dead bang on the
crystal, don't touch it and go back and tweak the IF alignment on that
frequency (at IF narrow bandwidth). A counter helps."

I believe the note came from A.B. Bonds. In any case, once I followed this
advice, my squealing monster aligned on the IF just fine. According to my
frequency counter, the magic number for my set is 456.9, not 455.0.

Any other useful tricks to know? I tried aligning the AVC by the book, but
didn't get good results. The AVC actually seems to work better when I set
it by ear, although I'm sure that sends a thrill of horror down the back
of a serious restorer.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

"Phil Nelson" wrote in message
ink.net...
I was tearing out my hair trying to align my SX-28's IFs at 455 kc when I
remembered this note in my old SX-28 notebook from about six years ago:

"Be aware that the crystal filter alignment instructions are wholly
incomprehensible. Bottom line is you do a rough IF alignment to 455 Khz
(bandpass set to IF narrow). Then you center the phasing cap and switch to
crystal sharp. Crank up your generator and try to find the center of the
crystal frequency. It's not easy, VERY twitchy, since the bandpass is
about
100 Hz. Once you have the generator centered dead bang on the crystal,
don't
touch it and go back and tweak the IF alignment on that frequency (at IF
narrow bandwidth). A counter helps."

I believe the note came from A.B. Bonds. In any case, once I followed this
advice, my squealing monster aligned on the IF just fine. According to my
frequency counter, the magic number for my set is 456.9, not 455.0.

Any other useful tricks to know? I tried aligning the AVC by the book, but
didn't get good results. The AVC actually seems to work better when I set
it
by ear, although I'm sure that sends a thrill of horror down the back of a
serious restorer.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Reminds me of trying to align to the crystal on an AR-88 I had years ago.
Had to use one of those looong handled pliers on the fine tuning of the Sig
Gennie for leverage and brace my arm to steady it and gradually move it
just........ SO.
I'm still not sure I got it right on.
Nelson

"Nelson Gietz" wrote

Reminds me of trying to align to the crystal on an AR-88 I had years ago.
Had to use one of those looong handled pliers on the fine tuning of the Sig
Gennie for leverage and brace my arm to steady it and gradually move it
just........ SO.
I'm still not sure I got it right on.


**** In that case you need an HP606B sig gen coupled to an HP 8708A
synchroniser,just purrrrrrfect!! :-)

Brian Goldsmith.

Brian Goldsmith wrote:

"Nelson Gietz" wrote

Reminds me of trying to align to the crystal on an AR-88 I had years ago.
Had to use one of those looong handled pliers on the fine tuning of the Sig
Gennie for leverage and brace my arm to steady it and gradually move it
just........ SO.
I'm still not sure I got it right on.

**** In that case you need an HP606B sig gen coupled to an HP 8708A
synchroniser,just purrrrrrfect!! :-)

Brian Goldsmith.


How about feeding a little RF from the detector circuit back into the
first mixer and align the IF transformers to match the crystal filter?
That way you have a crystal controlled signal generator that's exactly
on frequency.

--
Cyber stalking is a crime!

Michael A. Terrell
Central Florida

Ed Engelken pointed me to a great article in the February 2005 issue (#189)
of "Electric Radio." It is written by Bill Feldmann and includes a very
sensible explanation of how to align the SX-28 (esp. the crystal filter). In
discussing the SX-28's design, he also mentions a number of differences and
production changes.

Must-read material for any SX-28 owner!

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html