S-36/RBK-13 Redux
 

Some time ago a wrote to this group asking about
replacement parts for the S-36 dial drive. The reason was
that the small spur gear which is on the main tuning shaft
split. The split was such as to lock up the whole mechanism.
No parts were available alghough one fellow suggested a
place that might make one. After investigating the dial
mechanism I decided to see if I could repair the gear in
place. It seemed worth a try since the receiver is
constructed in such a way that removing the dial drive
requires substantial disassembly. Well, I was successful! I
was able to move the spur gear on its shaft and get some
slow curing epoxy resin on the knurled part of the shaft
where the gear was originally press fitted. I used a long
nosed Vise-Grip plier to clamp the gear in place and also
compress it so as to close the split. The split occured
along one of the teeth. This all took some careful alignment
of the parts in order than the gear was in the right place
for the dial stop mechanism to operate properly. The gear
seems to be working fine and the RX is back in business.
Since I removed it from its case I've taken the opportunity
to do a careful cleaning and will make sure there are no bad
caps hiding away, etc. While these are not wonderful
receivers from a performance standpoint they are still
interesting and are decorative if not terribly useful:-)
Unfortunately, the neither the IF or FM detector bandwidth
is wide enough for modern FM broadcast stations although it
doesn't sound too bad.
I have somewhere the original manual for this thing but
its in a box somewhere and I can't find it. I was able to
find manuals on the web but I am curious as to how the
RBK-13 version differs from the RBK-12. There is also an
RBK-15 but that has an additional, RF stage, untuned, to
reduce oscillator leakage.
My main point in posting this is to show that sometimes
makeshift repairs do work and not to give up when you run
across some antique that _looks_ unrepairable, it may not
be.


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

S-36/RBK-13 Redux
 

Hello Richard:

Repair of a radio, using what is available and by a method not envisioned by
the designers grants you a free pass to call yourself a true ham for one
more year.

You get a special award of merit for applying that much effort to a radio
that is not good for much, other than to get it running as intended then
putting it back on the shelf.

I hope I can one day apply that much energy into my WERS transceiver, which
transceives on 112 mc, more or less.

Good work.

Colin K7FM

S-36/RBK-13 Redux
 

"COLIN LAMB" wrote in message
m...
Hello Richard:

Repair of a radio, using what is available and by a method
not envisioned by the designers grants you a free pass to
call yourself a true ham for one more year.

You get a special award of merit for applying that much
effort to a radio that is not good for much, other than to
get it running as intended then putting it back on the
shelf.

I hope I can one day apply that much energy into my WERS
transceiver, which transceives on 112 mc, more or less.

Good work.

Colin K7FM
Thanks for the complement :-)
I'm not really a collector and like things to work
rather than be just display items. It was also a challenge.
Hallicrafters stuff is always interesting. They were
good at meeting market needs, sometimes quite innovative but
mostly quite conventional in design, rarely best of class
but very often very good values. The one outstanding area is
styling: mostly quite sexy looking, maybe the reason one
sees H equipment so often as props in old movies.


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

S-36/RBK-13 Redux
 

I have always wondered if Hallicrafters was responsible for much more than
we give it credit for. Originally, SX meant that it was a Hallicrafters
with a crystal filter, which was the deluxe model.

I think Hallicrafters became the model for manufacturers in Japan, and some
of the early Japanese radio successes used X in their model number. Then,
when cars came out, many had X or SX in the name. Perhaps these model
numbers can be traced back to the success of the Hallicrafters line?

73, Colin K7FM Newberg, Oregon

S-36/RBK-13 Redux
 

"COLIN LAMB" wrote in message
...
I have always wondered if Hallicrafters was responsible for
much more than we give it credit for. Originally, SX meant
that it was a Hallicrafters with a crystal filter, which
was the deluxe model.

I think Hallicrafters became the model for manufacturers
in Japan, and some of the early Japanese radio successes
used X in their model number. Then, when cars came out,
many had X or SX in the name. Perhaps these model numbers
can be traced back to the success of the Hallicrafters
line?

73, Colin K7FM Newberg, Oregon
Well, Kodak also liked X in names, usually indicating
an improvement. An example is the developer Microdol-X.
Originally called just Microdol an anti silvering agent was
added to prevent a sort of fog common in very fine grain
developers and the X added to the name. RCA did rather the
same thing, examples are the 77-D and 44-B microphones
released in improved models with an X added.
I think Hallicrafters was a master of marketing. Bill
Halligan found a niche in making affordable equipment for
hams and SWLs. The stuff always looked well styled.
Originally he used names like Skyrider. That's what the S in
the model numbers means. The SX-28 was a Super-Skyrider with
crystal filter. Hallicrafters also used some advanced
technology in a couple of places like the Lamb noise blanker
in the SX-28. Unfortunately, it didn't work very well in
that embodyment although similar noise blankers with
separate noise antennas did work well in other applications,
for instance the blanker supplied for the Collins KWM-2
transceiver.
Hallicrafters was also one of the first companies to
produce single side band equipment for the amateur.
I think sometimes features got ahead of performance. I
have somewhere (I wish I could find it) a WW-2 vintage
military communications technical manual which has a survey
of some available receivers in it. There are charts showing
spurious responses of three or four receivers. Among them
are the SX-28 in its military guise and the SPX-200
Super-Pro. The Super Pro chart has perhaps two spurs, namely
the expected image responses while the SX-28 chart looks
like a cornfield. Of course the Super-Pro cost almost twice
as much as the SX-28. BTW, the X in SPX also means it had a
crystal filter, which was optional although I've never seen
a Super-Pro without one.
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.


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

S-36/RBK-13 Redux
 

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

S-36/RBK-13 Redux
 

"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

S-36/RBK-13 Redux
 

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.

S-36/RBK-13 Redux
 

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

S-36/RBK-13 Redux
 

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.......

S-36/RBK-13 Redux
 

"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