[Hammarlund] SP-600-JX14 and my -JX1

[Richard Knoppow]

    I am curious which instructions he had. The crystal alignment 
is very simple. The filter is a patented design by Donald Orem, 
CE of Hammarlund at the time and first used on the Hammarlund 
HQ-120-X (the X means it had the filter). Orem's filter, unlike 
most others, does not detune when the bandwidth is changed. The 
gain remains fairly constant. There are a couple of silver mica 
caps in the filter which can go bad or drift which will screw up 
performance. The crystal frequency is the frequency the 455Khz IF 
must be adjusted to. The correct aljustment procedure uses an AM 
signal of about 2Khz with the carrier set at the crystal 
resonance and the bandwidth at maximum. The loading coil is set 
for maximum bandwidth (greatest recovered modulation). This does 
not seem intuitive but makes sense if you understand the theory 
of the filter. A very similar design is used by Collins in 
several receivers and in the TMC GPR-90.

On 8/22/2020 12:27 PM, Kenneth G. Gordon wrote:
> All this discussion makes me want to dig into my -JX1 now.
>
> Never been turned on since I got it. Looks complete.
>
> And it is full of BBODs....
>
> I remember my best Elmer, Woody Davey W7CJB (SK), rebuilt an SP-600 (which he had
> gotten from MARS) some 60 years ago, and had difficulty getting the crystal filter aligned
> properly.
>
> Seems as though the instructions in the manual(s) on how to do this were not completely
> accurate.
>
> He told me that when one switched on the crystal filter and adjusted things correctly, the
> signal-to-noise ratio should improve, and this should be shown by a rise (or at least not a fall)
> in the signal strength meter reading.
>
> I also remember how pleased he was when he got it working correctly.
>
> Ken W7EKB
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL