"k3hvg" wrote in message
. ..

BTW, I wonder if anyone out there has had experience
with the Hallicrafters version of the SP-600? I am
curious how its performance compares with the original.


If my info infers what I believe it does, the R-274 (nee
SX-73) was the first of the line. The Hammarlund
SP-600/R-274( ) came later as they beat out Hallicrafters
for the follow-on contracts. I have both receivers but
prefer the Hallicrafters. Tuning is much smoother and the
SX-73 has all the normal features of a general coverage
receiver. I do not, however, have a clue as how they
stack up regarding responses. I have heard rumors that
there was a Hallicrafters R-274 "B" version of but the
contract number is the same as the "original" R-274. I
suspect this was merely a simple production change of a
couple of components (capacitors) rather that a
substantive design change.
de K3HVG


It would be interesting to see when the Hallicrafters
project began. The Hammarlund SP-600 was first announced in
1948 but the advertizing features a drawing of what was
probably either a mock-up or prototype. Also, the details in
the ads vary in important ways from the production receiver.
The first SP-600's came out about 1950. I think some of the
changes were due to Hammarlund's realizing that the main
customer would be the military. I am not sure of the date of
the SX-73. The SX-73 is not a clone of the SP-600. Its a
different design in many respects but meant to meet the same
purchasing specs.
As far as the dial etc., a properly working SP-600 has
one of the smoothest tuning mechanisms around. Hallicrafters
may be as good but the SP-600 is so good that its unlikely a
different design would be significantly better. I also don't
know what you mean by "normal features". Both receivers have
about the same features and there is nothing missing from
the SP-600.
One improvement Hallicrafters made was to have filiment
regulators. The SP-600 is quite sensitive to line voltage
because the filiments in the oscillator and first mixer
change the frequency when they vary. I run mine on a Sola
transformer to avoid this problem.
I think at least some of the problems the SP-600 has
come from its being a continuation of the older Super-Pro
line with some attempt to make it look similar. So, the band
switch and tuning controls and the two dials _look_ like the
old Super-Pro layout with a main tuning control and a
bandspread control. I think Hammarlund also ran into
difficulties in trying to get the entire receiver, including
power supply, onto one chassis. This may be the reason they
abandoned the push-pull audio which was a feature of the
older SP series. While communications receivers are not used
for Hi-Fi the lower distortion of a good audio amp reduce
the effect of noise by eliminating all the distortion
products resulting from it in a poor amplifier. The amp in
the Super-Pro and most other communications receivers leaves
a lot to be desired.
I suspect the SX-73 may have proved too expensive for
Hallicrafters to make profitably but have no definite
information. They seem to be quite rare, I've only ever seen
one in the flesh.
BTW, after many years experience with SP-600's I've
come to the conclusion that a great many of them are
"working" but are still broken in some ways. The performance
of the RX is very good and complaints like stiff tuning,
poor frequency calibration, poor RF tracking, etc., come
from "broken" components.


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Richard Knoppow
Los Angeles, CA, USA