[Hammarlund] SP-600

[Richard Knoppow]

    I believe the original poster's complaint was that the dial 
calibration was accurate of the three lowest bands but not on the 
higher bands. The receiver is single conversion up to the 40 
meter band, that is on the three lower frequency bands. It is 
double conversion on the three higher bands. It makes sense to 
check the the second conversion oscillator for correct frequency.
    I suggested that the main tuning capacitor might be damaged 
because I have encountered two but, in fact, think its much more 
likely something has happened to the second conversion 
oscillator. Its easy enough to check.
    Each first conversion oscillator section is individual as you 
say. Actually, that is the case in most multi-band receivers. I 
have had to replace a bad silver-mica cap a couple of times 
because the frequency tracking was not good but that affected 
only one band.
    FWIW, a spec for dial accuracy is buried in the military 
manuals, it is +/- 0.25% I think the actual accuracy is probably 
better than this.
     I will also say that I have not found the SP-600 difficult 
to work on. There is mostly lots of room under the chassis. If 
one has to disassemble the tuning unit I think it would fall into 
the difficult category but I think that is extremely rare.
    As a last word, make sure that the dial pointer mechanism is 
set up correctly. The pointer should be centered on all bands, 
not tilted. I've used a strip of Scotch Magic tape to draw a line 
from the start mark to the beginning of the logging scale. Then 
move the pointer up and down and set both the dial and the 
pointer so it runs exactly vertically and straight along the 
dial. The end of the "gunsight" pointer should come just at or 
slightly above the calibration lines. The idea is that the thick 
pointer eliminates parallax and points exactly to a calibration 
mark which appears to be an extension of the pointer.
    For some reason Hammarlund never mentions this anywhere.

On 11/12/2019 8:54 AM, Stanley Adams wrote:
> Each band has its own osc section in the rotary turret.  My thoughts are
> that you are either doing something wrong or that the silver mica cap on the
> osc coil needs replacing.  I had to do that on one of the bands on my
> SP-600.  The unit acts as a double conversion on the low band or two but
> then goes to a triple (or double if the low band is single) but again each
> osc section is independent.
> 
> I suggest you download the military manual for the version you have and read
> the theory section well and understand it,  the SP-600 restoration is for a
> a seasoned restorer, not real simple in other words.
> 
> Stan Adams
> W4SBA
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL