[Hammarlund] Another SP-600-JX-17 lives!

[SP600historian@aol.com]

Russ and group,

First of all, congrats on getting it up and running! Secondly, here is the 
reason why your JX-17 is not acting as you would expect. This is a fault of 
"EVERY" JX-17 I have ever seen/operated. Andy Moorer has explained it in a 
very clear manner....this was taken from his 
webpage...http://www.jamminpower.com/main/sp600.jsp

Many people have asked me what is the difference between the "Diversity" 
receivers (The SP-600JX17) and all the other receivers. The diversity 
receivers look really cool because of the 3 red knobs on the front, but it is 
probably irrelevant for modern usage. In fact, the AGC structure, I feel, is 
not as good as the other receivers. Among other things, they inject the AGC 
voltage into the 6BE6 first mixer tube. The 6BE6 is not really designed for 
variable-mu operation. They run the first two RF stages at a relatively high 
gain all the time. I think this causes the AGC to do wierd things. I feel 
these receivers overload much more easily on strong signals. But if you like 
nifty red knobs, this is for you. It is also the most common single model of 
the SP-600 that was produced. It is a complex enough issue that I put 
together an entire page just on the diversity receivers: 

Hope this helps.




In a message dated 12/30/02 6:08:57 PM, wq3x@postoffice.ptd.net writes:

<< Hi all -

Just got this SP-600-JX-17 s/n 14266 beast recapped (un-black-beauty-ized)
with the help of the article by W2EC, Ray, and the wise words of advice from
Roy Morgan who said it MUST be done. There were 56 of the ugly critters. 25
of them were cracked and the best ones measured 250K on my 500V megger. Some
were down to 50K. I also replaced two cooked resistors which were likely due
to the caps breaking down. This makes a strong case for changing out the
black beauties in any SP-600 that still has them. I don't think it is a good
idea to even try out a receiver that still has the BBoDs.

I did try the receiver when I first got it and it did come on but the top
half of all bands was gone. (That's when Roy told me I had to change the
caps.) Now it works well and sounds good on all bands. I'm surprised at how
well it works even on SSB. The tuning is sooooo smooth. I also rebuilt the
filter cap can and probably will do the .05 and 5 10uF cans before I quit.

I found one quirk that I wonder if anyone else has seen.... When in the CW
mode, the S-meter moves up about 1/4 to 1/3 scale like it is responding to
the BFO injection signal. I see some of the other models had a 1K BFO
injection adjustment pot but the JX-17 has a fixed 100 Ohm resistor in the
cathode of V12. The AVC works fine on AM but the added signal from the BFO
buffer V12 when switched into the CW mode seems to be enough to make the AVC
diode conduct. Is this normal?

Thanks for all the recent posts about recapping that finally made me start
this project. It seems like a lot of work and it is! And a lot longer than 2
evenings! Their were all sorts of other things to fix that I found during
the recapping but as everyone says, it's worth it.

73, and Happy New Year,

Russ WQ3X

 >>



Les Locklear
Gulfport, Ms.
SP-600 Historian
http://www.hammarlund.info/