[Hammarlund] SP-600 setting up dials

[Richard Knoppow]

    In order for the dial calibration to be correct the dial 
and pointer must be properly aligned. While it would be 
simple to get both right with a combination square it turns 
out that there is really no way to get it against the dial 
in the right place so an indirect method must be used. I 
will describe that method.
    The first step is to remove the front panel so that you 
have access to the dial mechanism.
    Its important that the pointer be placed so that it runs 
straight up and down the dial and is not at an angle.
The pointer is on an arm which is attached to a slider which 
moves up and down with the band switch. The pointer is held 
to the arm by two screws in its side. These screws allow the 
vertical position of the pointer to be adjusted. It should 
be set so that the tip of the pointer comes just to the 
reference line for the band in use or perhaps a tiny bit 
above it. It should not be as high as the minor calibration 
marks. The pointer is made like a gunsight in order to 
eliminate parallax even though its at some distance from the 
dial. When its at the right height and the eye aligned with 
it the calibration lines will appear to be extensions of the 
pointer.
    The arm is held to the slider by two screws which face 
front. The attachment of the arm allows the pointer to be 
adjusted for position. It must run exactly parallel with the 
dial markings.
    The main dial has a reference mark just below the lowest 
frequency band at the counterclockwise (low frequency) end. 
This line is in line with the end of the box with the 
logging scale in it. I put a length of transparent tape on 
the dial over the two marks and extend a line between them. 
This gives a reference line across the entire face of the 
dial.
    Now, both dials are held in place by clamps. The clamps 
each have four screws. To align the main dial loosen the 
screws just enough to allow slipping the dial. set the 
bandswitch at the low range and adjust the dial so the 
pointer is on the line. Now, either push the pointer up by 
hand or move the bandswitch to the high range and see where 
the pointer is. It should be right on the line at the top. 
If not juggle the dial position and pointer position a 
little and try again. Between the dial slipping and pointer 
tilting you will get to a point where the pointer runs 
exactly on the line at all bandswitch positions. This is the 
correct setting. Make sure the pointer height is correct as 
noted above. Tighten everything. Make sure the dial clamp 
screws are really tight and that the dial can't slip. If it 
slips at all you will have to take the front panel off again 
to tighten it.
    Set the pointer for the logging dial at the  reference 
line with the dial at the low end stop and make sure its 
vertical. That completes the main dial. Remove the tape with 
the reference mark. Now set the logging dial and pointer by 
setting the tuning at the low end. Loosen the clamps on the 
logging dial and center it, again juggle the pointer and 
dial to get the pointer vertical and on the reference mark 
at the end of the dial. You may be able to use a small 
square on this pointer. Since both logging pointers are 
fixed they are much less difficult to adjust. Again make 
sure the clamps on both dials and the pointer screws are 
tight. Replace the front panel and align the receiver.
    Once done this will probably never have to be touched 
again.
    Another note since we are talking about the dial: the 
SP-600 is a notorious dial lamp eater. This can be fixed by 
installing a dropping resistor in the line to the lamps. 
There is a service note in the Hammarlund literature 
collection on installing an IF gain control in diversity 
receivers. Included in this note are instructions for adding 
the dropping resistor. Its well worth the effort since it 
will at least double the life of the lamps.
    Note that a 5% reduction in voltage will double the 
life, a 15% reduction will extend the life by ten times! A 
15% reduction dims the lamps only a little.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com