[Hammarlund] Hammarlund drift

[Glen Zook]

Unfortunately, it has been my experience with many
Hammarlund receivers that I have worked on over the
years that most models tend to drift, especially on
the 14 MHz band and higher in frequency.

The series that started with the HQ-120 (HQ-120,
HQ-129X, HQ-140X, HQ-150X, and the HQ-145 series) are
a "pleasant" exception to this rule.  That series of
receivers are basically the same design, just tube
type changes and different cabinets, tend to be very
stable after about 30 to 60 minutes "warm up".  The
other Hammarlund receivers tend to still drift even
after several hours of operation.

I have found that the HQ-110 and HQ-170 series usually
drift so bad on 6 meters (and on 2 meters in the "VHF"
versions) as to make SSB operation a bit difficult
(you have to keep your hand on the tuning dial).  They
work "OK" on AM since you don't have to keep that
close in frequency, but most of them tend to drift
more than I like to keep SSB tuned in.

The SP-600 series is just as bad on the higher
frequencies as well.  Hammarlund did come up with
crystal control for the SP-600 series as the "JX"
option which basically "cures" the stability problem. 
Other than drift, the receivers do a pretty good job
(sensitivity, overload, etc.).

Back when I was a senior in college (like 1966 time
frame!), I owned my first HQ-140X receiver.  At the
time I had a Model 15 teletype machine.  Reuters had a
New York - Havana news link that ran basically 24
hours a day.  At the time they were using 750 Hz shift
and 66 wpm.  Although the Model 15 was set up for 60
wpm, it would copy the 66 wpm without any trouble.  I
found that after about an hour's warm-up for the
HQ-140X that I could tune in this link, turn on the
Model 15, and come back hours later to "perfect" copy.
 The receiver seemed to hold within about 100 Hz of
the desired frequency.  This was as good as anything
else that was available at the time and better than at
least 90 percent of the receivers.

Anyway, below 14 MHz, and often even on the 14 MHz
band (20 meters), the Hammarlund receivers usually
work fine.  But, the higher you go in frequency the
more that they seem to drift.

Of course, Hammarlund isn't the only brand that does
this.  Most of the Hallicrafters receivers and many of
the National receivers are in the same "boat",
especially the "general coverage" versions.  Those
receivers, like the Hallicrafters SX-115 that use
basically crystal controlled converters into a lower
frequency receiver (like Collins, Heath SB-Line, etc.)
are pretty stable as well.  It is those receivers that
use a different oscillator for each band that have the
most problems.

Glen, K9STH


--- Mike Taylor <reel2reel@hotmail.com> wrote:

These rigs were designed to be stable, so if yours is
drifting all the time something is wrong.

=====
Glen, K9STH

Web sites

http://home.comcast.net/~k9sth
http://home.comcast.net/~zcomco

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