"Avery W3AVE" wrote in message
ups.com...

Richard Knoppow wrote:
I've never seen an SP-400-SX, there certainly was an
SP-200 with this coverage. It differed from the others in
having shunt-fed RF plate coils rather than series fed.
This
resulted in somewhat sharper tuning of the RF stages and
lower image response. I am not sure if the same
arrangement
was used for either SP-400 models. These are still very
respectable receivers.
---
Richard Knoppow
Los Angeles, CA, USA


There's a 400-SX on ebay right now. As a major Hammarlund
fan, I'm
tempted, but only mildly. It's been considerably modified,
and by the
time packing fees and shipping are added to the BIN figure
or something
close to it, we're in SP-600 territory. It's at
http://cgi.ebay.com/ws/eBayISAPI.dll...MEWA%3AIT&rd=1.


I am also skeptical about home made modifications. Its
easy to get the AVC unbalanced and create other problems.
My BC-779, bought surplus some 40 years ago, was heavily
modified to follow circuits published in CQ magazine. After
experimenting with these and my own modifications I restored
the original circuits and found they performed just about as
well, plus I eliminated some circuit loading of the RF tuned
circuits. The original uses what today would be considered
quite noisy tubes but one must take into account the
naturally occuring noise in the HF communication bands. Its
quite high so often a front end which is very quiet does not
buy much. Better to have one which can take overload. The
one worthwhile modification I've found for the SP-200 series
is the use of regulated voltage on the local oscillator and
mixer screen. This eliminates the frequency variation when
the RF gain changes.


--
---
Richard Knoppow
Los Angeles, CA, USA