[Hammarlund] SP 600 BANDSPREAD

[Richard Knoppow]

----- Original Message ----- 
From: "Pat & Rich McKinney" <pmcknney at bellsouth.net>
To: <hammarlund at mailman.qth.net>
Sent: Sunday, September 23, 2012 12:13 PM
Subject: [Hammarlund] SP 600 BANDSPREAD


> DE WB4VFN RICH
>    I'm working on a SP600 jx-1 for a friend.  I have a 
> question about the tuning.  Is it right for the bandspread 
> dial to not land on zero at each even mc on all bands.  I 
> don't see how it can.  If that is the case where is it 
> supposed to zero on an even mc?  The old thing is not very 
> sensitive at all and way off frequency.  So I guess an 
> alignment is in order.  Any help appreciated to get this 
> old boat anchor back in service.  73  Rich

     If the dials and pointers are aligned correctly the 
main pointer should rest on the reference index at the far 
low end of the dial, its just below the calibration.  The 
main dial logging scale should be at zero and the "band 
spread" dial should also be at zero.  The band spread dial 
should be a zero again at the beginning of each numbered 
segment on the main logging scale.  Check the pointer to see 
that it lines up with the index mark on the lowest band and 
the edge of the box for the logging scale on the highest 
band. If it does not (if its tilted) its necessary to remove 
the front panel and align the dials and pointers.  If you 
need to do this I will give you details, the procedure is 
not in the handbook. If its off you will not be able to get 
the calibration right on all bands.
     Before doing an alignment remove the top cover from the 
tuning unit and look at the main capacitor.  All of its 
sections should be centered and the stators should line up 
vertically with the rotor. The rotor plates should NOT be 
bent. If someone has indulged in plate bending its probably 
because the stators are not centered or the dials were 
mis-aligned. Unfortunately, its almost impossible to 
straighten out the plates.  The plates are slit on the sides 
which makes it look as though they are supposed to be bent 
but they are not.
    If the stators are off center its necessary to remove 
the entire capacitor assembly and align the stators.  Its 
not as difficult as it sounds. The stators are clamped in 
place with screws and fiber washers and can drift with time. 
Why Hammarlund chose this method of construction is beyond 
me. In any case they can be aligned with feeler blades to 
get them centered and a straight edge to get the stators 
aligned vertically with the rotor. If all are centered 
correctly the frequency calibration and RF tracking should 
be very good.  The centering also affects the stability, 
best stability is had when properly centered.
     In general the alignment procedure in the handbook 
works.  There was a special tool for alignment but its 
possible to work with an insulated screwdriver.  You may 
have to rock the turret to get the adjustments to align with 
the holes.
     Set the signal generator to the exact frequency of the 
crystal filter to do the rest of the IF alignment.  I use 
400 hz modulation for the IF.  the crystal filter has two 
adjustments: one is just peaked at the IF frequency, the 
other should be set up with the crystal in its widest 
bandwidth position using about a 2 khz modulation. Adjust 
for _maximum_ bandwidth.  When done this way the bandwidth 
should become progressively narrower as indicated by the 
bandwidth dial.  Hammarlund had a patent on this crystal 
filter which is excellent and was also used by Collins and 
TMC among others.
     If the sensitivity on some bands is poor it may be bad 
caps.  The earlier SP-600
s had paper caps, mostly Black Beauty types. If yours has 
paper caps, particularly BB;s they must _all_ be changed. 
This is a tedious job but the receiver is fairly easy to 
work on.  There is information on doing the recapping on the 
web. You will have to remove the RF strip from the tuning 
unit. Be extremely careful to cock the bandswitch in between 
two bands. If you do not you will destroy the contacts on 
the RF switch.
    There is a lot more.  These are very fine receivers, and 
I think at least some of the criticism of them comes from 
the fact that there are a lot of them around which are 
working but sick.  They are worth the effort to make right.


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