[Hammarlund] sp-600 align

[Richard Knoppow]

    The crystal frequency is 3.5 Mhz. 3.955 is the second IF 
frequency, i.e. 455 Khz plus 3.5 mhz = 3955 Khz.
    The crystal frequency is NOT adjustable. It can be measured 
by removing the shield from the second oscillator, also called 
the IFO, and wrapping a few turns of wire around it. The other 
end going to a second receiver.
    If the crystal is way off (unlikely) it must be replaced.
    If the receiver works at all you can align the IF using a 
signal generator at any frequency in the single conversion range. 
Tune in the signal generator and peak it using the crystal 
filter. That will establish the IF frequency. It will be at the 
exact IF crystal filter frequency. Then, set the IF bandwidth at 
3 Khz and peak all the 455 Khz IF adjustments for maximum. Those 
are L-32, L-36, L-38, L-41, L-42, leave the crystal filter 
adjustment for later. Now, switch to band 4 and set the signal 
generator for a frequency on that band. Tune it in and center it 
using the crystal filter, now switch back to 3 Khz bandwidth. Now 
peak L-31, L-33, L-34 for maximum output.
    If the receiver works this is a bit easier than connecting 
the signal generator to the grid of the first converter tube 
which needs a socket adapter to do.
    I will go over the crystal filter adjustment separately.
    You should be able to peak both IFs as above, or if you have 
an adapter by the book method.
    I have mentioned the pointer before, have you looked to see 
if it runs straight up and down. Sometimes they are not mounted 
correctly and run at an angle. I should not. Also, the main dial 
should be set so that the reference mark at the low end of the 
dial is exatly on the pointer at the stop. When it is the pointer 
should move up along a line to the first mark of the logging 
scale at the top. It is important that the dial be correctly 
mounted on its shaft. The bandspread dial also should be centered 
but is not critical to the calibration accuracy. Adjusting the 
dials and pointer require removing the front panel. This is not 
difficult but is a lot of work. When its removed you can also 
make sure the dial gears are clean and lubricated.
    The dial mechanism of the SP-600 is the smoothest I have ever 
encountered. If yours is not smooth, free of drag and backlash, 
there is something wrong, probably dirt.
     Keep in mind that when working correctly the SP-600 is an 
outstanding receiver. It may not be ideal for ham use but it was 
never intended for that.
     FWIW, the SP-600-JX 17, the one with the red knobs, was over 
$2000 in the late Hammarlund catalogs and the standard model was 
nearly as much. The 17 was intended for use in dual diversity 
systems for fixed-point-to-point commercial communication 
services. The modifications were similar to those worked out by 
Northern Radio for receivers it supplied for its dual diversity 
systems. Dual diversity used two spaced antennas, each with a 
separate receiver and a combiner such that the output was always 
the result of the strongest signal. It eliminated the 
preponderance of fading. Depending on who's numbers you read the 
power advantage was on the order of 10db.

On 11/13/2019 9:43 AM, wb3fau55 at neo.rr.com wrote:
> Next question is the 3.50 mc 2nd osc xtal. Referring to the paperwork
> it says 3.50mc, but also says 3.955 for precision alignment. So if
> this is out of range, will that affect the tracking spread?
> 
> 	I will test now...Russ.
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL