"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.


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

Richard Knoppow wrote:
"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.


Truth told, you're about right..... The SP-600 does have virtually the
same features. I'd forgotten that the '600 does have a filter phasing
control. I guess the only feature might be the antenna tune control but
one could argue the efficacy of that! The only other thing might be the
physical compression/calibration of the amateur bands. The
Hallicrafters has a bit more spread than the SP-600 on most ham bands.
Beyond that, your comment is appropriate.

The other comment might be that re-capping an early SP-600 can be
laborious, especially when replacing the caps on the turret modules and
inside the RF side channel. Not difficult, just laborious. Later
models don't have that issue, of course.

Of course, removing the complete turret assy from the SX-73 is no
picnic, either.......I should have added!!!!

If I could have said it all in one message...................

The contract info on mine says:

ORDER No. 25557-PHILA-49-7C.

Looks like it would be 1949 for this one.......

"k3hvg" wrote in message
...
If I could have said it all in one
message...................

The contract info on mine says:

ORDER No. 25557-PHILA-49-7C.

Looks like it would be 1949 for this one.......

There is a list on one of the Hammarlund sites with a
list of military contracts for the R-274 on it. I don't know
when the earliest order for the Hammarlund version was put
made.
About the crystal filter: Hammarlund owned the patent
for the version of the filter used on its receivers and,
later, by Collins and others. The original Lamb filter had
problems with broadening it out, it tended to shift center
frequency, and the notch was not symmetrical. Hammarlund's
version allowed broadening out enough to use on phone and
had pretty constant gain. Also, the use of a double phasing
capacitor allowed keeping the peak centered when varying the
notch frequency. In general T-notch filters work better but
the crystal was the best available at the time.
The Hallicrafters S-73 looks well worked out. I think
they simplified the turret contact arrangement quite a bit
but I don't know how well it works in practice.
Hammarlund made the mistake of taking Sprague at their
word about _Black Beauty_ caps. These were _supposed_ to be
deluxe, low leakage caps with a wide temperature tollerance.
The dielectric as a combination of paper impregnated with
plastic. They _should_ have been very long lived and of
good performance. Unfortunately, something went badly wrong.
My own suspicion is that the casing material had some
serious problem. Many of these caps are found split and not
just at the mold seams. The caps inside are distorted in
shape. Of course, I don't know that they were wound round
originally but the bad ones are flattened in various ways, I
suspect distorted by the shrinkage of the case. Sprague also
made a similar cap with radial leads called an "Orange
Drop". These were dipped in epoxy rather than being molded
in whatever was used for the BB caps. I've never heard that
these were particularly trouble prone. BB caps were used in
some very deluxe equipment such as instruments made by
General Radio and Hewlett-Packard. I first heard that they
were bad guys when I was a teen ager so the problems must
have shown up pretty quickly. I don't think all BBs are bad
becuause Sprague continued to advertise them after the time
the military issued the MWO for chaning out all of them in
the SP-600. There are probably people who know first hand
what happened.
There sure are a lot of questions about old equipment
which were probably answered in the manufacturing data but I
doubt if much, if any, of that exists because most
businesses see keeping historical records as unprofitable
and return on investment is what makes the world go 'round.


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