[Hammarlund] VXO for JX-14 Diversity receiver

[James A. (Andy) Moorer]

Dear Hammarlund enthusiasts:

I just got my first two SP-600JX-14 "Diversity" model receivers. I was a bit
startled at the differences. First off, the 3.5 mHz oscillator is a
Colpits-type rather than a tuned-grid oscillator. It has a low-pass filter
connected to a beverage-type connector on the back marked IFO. There is a
switch on front that controls power to the 6C4 (as well as S4 switching that
same power) that is labeled "IFO EXT/INT". I assume what is going on is that
you can switch off the local 3.5 mHz oscillator and pick up some external
3.5 mHz feed. I guess the idea is that if you have several receivers, you
might want to synchronize all the 3.5 mHz oscillators. Using the Colpits
oscillator lets you take the signal off the plate, which is presumably a
much lower impedance.

The other big difference is in the VXO. It is LOTS more complicated! I took
a couple of pictures of this fancy VXO and posted them on the hammarlund
history site. They are not public, but are available to peruse at the
following URLs:

http://www.hammarlund.info/gif/vxo1.gif
http://www.hammarlund.info/gif/vxo2.gif

Note that it has two bakelite parts shelves. You can't see under the top
one, but there is a transformer underneath it.

I will try to trace out the connections, but It is a bit hard to figure out
what values the inductors have. I suppose I could take them out and measure
them someday.

Anybody ever see any schematics of these? I sure would like a definitive
schematic and parts list for these changes.


-- 
James A. (Andy) Moorer
Adobe Systems