RadioBanter - SP-600 JX-17 problem

"wn6yqs" wrote in message
...
Have recently purchased a SP-600 JX-17 in "working/as is"
condition.
the good.....it works on the lower 3 band ranges. The bad,
it is "as
is" aka nothing (no signals, nouise, static, etc) at all
on the higher
3 band ranges. Am interested in any initial
troubleshooting ideas
folks may have. Thanks in advance for the assistance -
winter is
coming and I'll need the tube heat!

The problem is that the second conversion stage is not
working for some reason. The first thing to look at is the
position of the IFO switch on the front panel, this is the
left hand red knob. If its in EXT the set will not work on
the top three bands.
The JX-17 version of the SP-600 differs little from
other models but some of the differences are important. This
receiver was meant to operate in groups of two or three in
space diversity systems. This is simply a way of improving
radio circuit performance by combining the signals from two
or three spaced antennas since the signal variation due to
certain kinds of fading will be different for each.
Diversity combiners may need to have access to various
internal signals from the receivers connected to them. The
SP-600-JX was designed to fit these needs and obviate the
need to modify the standard models. To operate as a
stand-alone receiver the HFO switch must be set at VAR, and
the IFO and BFO/AVC switches set for internal.

There is a great deal of information available for the
SP-600 on the web. Complete handbooks and military repair
manuals can be found. See for instance:
http://www.jamminpower.com and of course the BAMA site:
http://bama.sbc.edu/ For the last use the alternative site
for downloading, its very much faster.
Also see: http://www.hammarlund.info/
The SP-600 is a very fine receiver. I have come to the
conclusion that there are a great many of them which "work"
but are really pretty sick. While they are fairly easy to
work on (other than being very heavy) one needs some special
knowledge to get them up to their capability.
A word of caution: NEVER BEND TUNING CAPACITOR PLATES
they should be straight and parallel. If the frequench
calibration is off it _can_ be from a misalignment of the
capacitor stators and rotors but this is NEVER cured by
plate bending.
Many SP-600s were made using the notorious Sprague Black
Beauty capacitors. While these were made and sold to be
extra-reliable high performance units they had manufacturing
problems and proved to be very unreliable. It is common
practice to replace _all_ of them (I think its 48) in the
receiver. Many military radios will have modified with
ceramic caps which are very reliable and long lived.
There are a lot of SP-600 fans here so I think you will
be able to get answers to most of your questions.

--
Richard Knoppow
Los Angeles
WB6KBL