Hallicrafters SX-42 Alignment
 

I am having some problems aligning my SX-42. I replaced all the paper
caps and a number the aged resistors that are usually found to be way
out of spec.

I find that I am having problems obtaining proper dial calibration. I
can generally set the high end of the band using the trimmer cap. But
after I set the low end by adjusting the coil, the high end is off
again. Repeated efforts don't significantly narrow the gap.

On the highest band, the problem is most pronounced. The 60 MHz low
point was dead on to start with. However the high end is 1 to 2 MHz off
and there is not enough adjustment in the trimmer cap to fix this.

I wonder whether anyone else has had this type of problem and found a
solution? I am considering doing some further re-capping, but it is my
understanding that generally this is not necessary.

The one other factor, which I have yet to fully explore, is the B+.
Apparently, at one point the power transformer was replaced and the B+
is about 30 volts higher than spec. I am going to try putting a
dropping resistor in to bring it down to the 250 volts indicated in the
manual and attempt one more alignment, starting with the IF's. I wonder
whether anyone has encountered this and whether this 10+% voltage
overage is a problem to worry about?

Many thanks in advance.

Irv,

I have the Sams, Rider and Hallicrafters manual and I am following those. The
procedures seem to be the same, except the numbering scheme for the various
adjustment points. They don't mention anything about using the logging scale and I am
not familar with that process.

I am using my Cushman 5110 service monitor, checking the freq with an HP counter
which has been compared to a GPS 10 MHz. standard, so I know that the signal I am
feeding it is good.

Thanks

Irv Finkleman wrote:

Frederick Bray wrote:

I am having some problems aligning my SX-42. I replaced all the paper
caps and a number the aged resistors that are usually found to be way
out of spec.

I find that I am having problems obtaining proper dial calibration. I
can generally set the high end of the band using the trimmer cap. But
after I set the low end by adjusting the coil, the high end is off
again. Repeated efforts don't significantly narrow the gap.

On the highest band, the problem is most pronounced. The 60 MHz low
point was dead on to start with. However the high end is 1 to 2 MHz off
and there is not enough adjustment in the trimmer cap to fix this.

I wonder whether anyone else has had this type of problem and found a
solution? I am considering doing some further re-capping, but it is my
understanding that generally this is not necessary.

The one other factor, which I have yet to fully explore, is the B+.
Apparently, at one point the power transformer was replaced and the B+
is about 30 volts higher than spec. I am going to try putting a
dropping resistor in to bring it down to the 250 volts indicated in the
manual and attempt one more alignment, starting with the IF's. I wonder
whether anyone has encountered this and whether this 10+% voltage
overage is a problem to worry about?

Many thanks in advance.

Are you following a specified alignment procedure or just going
by the old 'hi end cap, lo end coil' concept? I ask because some
alignment procedures dont go right to the high end or the low end
but to a point just inside the range, for example assume a logging
scale of zero (low end) to 100 (high end). The high end alignment
would be carried out at about 80 on the scale, the low end at 20.
If all else fails you might try something like that. Hope this helps.
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--------------------
Irv Finkleman,
Grampa/Ex-Navy/Old Fart/Ham Radio VE6BP
Calgary, Alberta, Canada

I find that I am having problems obtaining proper dial calibration. I
can generally set the high end of the band using the trimmer cap. But
after I set the low end by adjusting the coil, the high end is off
again. Repeated efforts don't significantly narrow the gap.

========================

It is possible to get the local oscillator (LO) set on the wrong side
of the signal frequency when aligning the higher frequency bands. If
you get the LO on the high side of the signal frequency on one end of
the band and on the low side on the other end, the calibration and
sensitivity will never be good. Continued re-adjustment with the LO
on the wrong side of the signal will result in the problems you are
having. One of those hand-held frequency counters can "sniff out" the
LO and tell you exactly where it is. Lacking that, another receiver
with good calibration can be used to identify the LO and determine if
it it is on the high side of the signal frequency where it belongs.

My SX-42 dial calibration is quite accurate, so bad calibration is not
to be expected with that receiver.

Best Regards,

Ed Engelken
Canyon Lake, TX

In article ,
(Ed Engelken) writes:

It is possible to get the local oscillator (LO) set on the wrong side
of the signal frequency when aligning the higher frequency bands. If
you get the LO on the high side of the signal frequency on one end of
the band and on the low side on the other end, the calibration and
sensitivity will never be good.

Very good advice, and a common cause of trouble with single-conversion rx.
Such cross-alignment can also cause self-oscillations and/or totally dead spots
somewhere on the dial.

Another way to check for this error is to flip the signal generator (or the
radio) to the expected image frequency, and verify that the image is on the
same side of the "real" frequency at both ends of the dial. Many receiver
manuals mention this check.

I have the SX-42 docs but not real handy. Something to look forward to when I
try to get my '42 up to snuff (it is almost deaf now, but works on all bands
and modes).

Are there still any commercial mobiles on the 30-50 MC FM band?
73, Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

Thanks to all who replied.

It turns out that the problem with this radio was with the bandspread. When
I got it, the bandspread dial was loose and I set it to what I thought was
the correct zero position. Turns out that this was about 90 degrees off.
By experimenting, I found the zero point where all bands track correctly.
Now it can be set properly on all bands.

Eventually, I will have to tweak the crystal phasing, but that is a project
for another time.

Ed Engelken wrote:

I find that I am having problems obtaining proper dial calibration. I
can generally set the high end of the band using the trimmer cap. But
after I set the low end by adjusting the coil, the high end is off
again. Repeated efforts don't significantly narrow the gap.

========================

It is possible to get the local oscillator (LO) set on the wrong side
of the signal frequency when aligning the higher frequency bands. If
you get the LO on the high side of the signal frequency on one end of
the band and on the low side on the other end, the calibration and
sensitivity will never be good. Continued re-adjustment with the LO
on the wrong side of the signal will result in the problems you are
having. One of those hand-held frequency counters can "sniff out" the
LO and tell you exactly where it is. Lacking that, another receiver
with good calibration can be used to identify the LO and determine if
it it is on the high side of the signal frequency where it belongs.

My SX-42 dial calibration is quite accurate, so bad calibration is not
to be expected with that receiver.

Best Regards,

Ed Engelken
Canyon Lake, TX