Hallicrafters SX-28 tuning gearbox restoration
 

Hallicrafters SX-28 owners may be interested in this article about restoring
the SX-28 tuning gearbox:

http://antiqueradio.org/SX-28Gearbox.htm

Thanks to Doug Moore for writing this detailed saga, and to Hallicrafters
Collectors International for giving permission to mirror it on my website.

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

"Phil Nelson" wrote in message
nk.net...
Hallicrafters SX-28 owners may be interested in this article about
restoring
the SX-28 tuning gearbox:



Awwwwk! NOW I understand why you painted the front-panel!
You saved a parts set from oblivion! My hero!

Pete

Awwwwk! NOW I understand why you painted the front-panel!
You saved a parts set from oblivion! My hero!

All credit goes to Doug Moore, the author of this article. (I'm just the
messenger :-)

Regards,

Phil Nelson

Phil Nelson wrote:
Hallicrafters SX-28 owners may be interested in this article about restoring
the SX-28 tuning gearbox:

http://antiqueradio.org/SX-28Gearbox.htm

Thanks to Doug Moore for writing this detailed saga, and to Hallicrafters
Collectors International for giving permission to mirror it on my website.


Excellent article......I hope I never have to actually do this!

Incidentally, I've discovered a pretty good way to remove those C rings.
There are several of them on the gear train of a direlict Hammarlund
SP-600 I'm restoring now. Description follows:

Get two pairs of small needlenose pliers. Ideally, these should be the
kind that are somewhat flat on the ends rather than pointy.

Orient the C ring so that each end of the "C" is pointed towards the
bottom (like an inverted U)

Position the first pair of needlenose so that one tip is resting on the
end of the shaft, toward the top, and the other tip is resting on the
left end of the C ring.

Position the second pair of needlenose so that one tip is resting on the
end of the shaft, toward the top, and the other tip is resting on the
right end of the C ring.

Now, carefully apply a gentle squeezing to the handles of both pairs of
needlenose pliers simultaneously, and the C ring will begin to spread.
When it is about halfway off, you can then insert a small screwdriver
and gently pry the C ring the rest of the way off. Be careful not to
score the shaft.

To re-install a C ring you have removed, simply place the spread-open C
ring back on the shaft, and then take a pair of long nose pliers and
squeeze the edges of the ring until it closes as much as it can on the
shaft. Voila!

-Scott




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Need a schematic? check out the Schematic Bank at:
http://techpreservation.dyndns.org/schematics/

Archive of alt.binaries.pictures.radio binary postings:
http://techpreservation.dyndns.org/abpr/

Did you read the part about restringing and the dial directions? That
gets me wondering about the direction issue again...

I think the consensus was that SX-28s seem to have come working both ways
from the factory. My personal preference would be to have the dial move in
the same direction as the knob, but some folks (including me) swear they
have an original-looking SX-28 that moves the opposite way.

I still haven't decided whether that preference is strong enough to make me
cut off the perfectly-functional new bandstring and install a new one that
works the other way. Guess I'll have to decide by the time I finish
repainting/relettering the front panel. Once the panel is in place, it's
trickier, although not impossible, to replace that string.

Regards,

Phil Nelson

C-clips

It sure helps if you have 3 hands when using this method ;-)

Al, W8UT

Incidentally, I've discovered a pretty good way to remove those C rings.
There are several of them on the gear train of a direlict Hammarlund
SP-600 I'm restoring now. Description follows:

Get two pairs of small needlenose pliers. Ideally, these should be the
kind that are somewhat flat on the ends rather than pointy.

Orient the C ring so that each end of the "C" is pointed towards the
bottom (like an inverted U)

Position the first pair of needlenose so that one tip is resting on the
end of the shaft, toward the top, and the other tip is resting on the
left end of the C ring.

Position the second pair of needlenose so that one tip is resting on the
end of the shaft, toward the top, and the other tip is resting on the
right end of the C ring.

Now, carefully apply a gentle squeezing to the handles of both pairs of
needlenose pliers simultaneously, and the C ring will begin to spread.
When it is about halfway off, you can then insert a small screwdriver
and gently pry the C ring the rest of the way off. Be careful not to
score the shaft.

To re-install a C ring you have removed, simply place the spread-open C
ring back on the shaft, and then take a pair of long nose pliers and
squeeze the edges of the ring until it closes as much as it can on the
shaft. Voila!

-Scott

Al Parker wrote:
C-clips

It sure helps if you have 3 hands when using this method ;-)

Al, W8UT

Three hands not required. I can get one of these rings off in about two
seconds using the described method, with two hands, no problem.

I have seen the "official" tool that was originally used to
attach/remove these rings, and it is a fairly complicated
gizmo....Probably unobtainable unless special-ordered. With that tool,
it's a one-handed job.

-Scott




--
DO NOT REPLY TO THIS MESSAGE AT THE EMAIL ADDRESS ABOVE!
Instead, go to the following web page to get my real email address:
http://member.newsguy.com/~polezi/scottsaddy.htm
(This has been done because I am sick of SPAMMERS making my email unusable)

Need a schematic? check out the Schematic Bank at:
http://techpreservation.dyndns.org/schematics/

Archive of alt.binaries.pictures.radio binary postings:
http://techpreservation.dyndns.org/abpr/

"Scott W. Harvey" wrote in message
...
Al Parker wrote:
C-clips

It sure helps if you have 3 hands when using this method ;-)

Al, W8UT

Three hands not required. I can get one of these rings off in about two
seconds using the described method, with two hands, no problem.

I have seen the "official" tool that was originally used to
attach/remove these rings, and it is a fairly complicated
gizmo....Probably unobtainable unless special-ordered. With that tool,
it's a one-handed job.

-Scott

It's sorta like those plastic Heyco cord strain reliefs that pinch down on
the cable, and then you push it thru a double D hole in the chassis. They
are a b@@ch to put in with pliers, but with the heyco tool, it's a simple
one handed job.
Regards,
Tom/

Phil Nelson wrote:
Did you read the part about restringing and the dial directions? That
gets me wondering about the direction issue again...

I think the consensus was that SX-28s seem to have come working both
ways from the factory. My personal preference would be to have the
dial move in the same direction as the knob, but some folks
(including me) swear they have an original-looking SX-28 that moves
the opposite way.
I still haven't decided whether that preference is strong enough to
make me cut off the perfectly-functional new bandstring and install a
new one that works the other way. Guess I'll have to decide by the
time I finish repainting/relettering the front panel. Once the panel
is in place, it's trickier, although not impossible, to replace that
string.
Regards,

Phil Nelson

Phil:
Is there supposed to be a mechanical stop to keep one from turning the band
change dial too far and screwing it up, or from turning it the wrong way??

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

Is there supposed to be a mechanical stop to keep one from turning the
band change dial too far and screwing it up, or from turning it the wrong
way??

Yah, there definitely is a stop at both ends. That is, if you try to go
below the lowest band, or above the highest one, you hit a stop. My second
set is in pieces right now, so I can't investigate.

There is a detent mechanism at the rear end of the bandshaft which might
have a hard stop. Again, this thing is all over the workbench, so I can't
say for sure. But that's where I would put a stop if I were designing a
multi-band radio.

Below is a diagram for stringing the tuners. It mentions a blocking washer,
and also says that you may break the cord if tension and knot position in
the tuning is not correct.

http://antiqueradio.org/art/temp/SX28DialStringing.jpg

I can't testify that this information will be identical for SX-28 and
SX-28A. Your mileage may vary :-)

From using my first SX-28, I have to say that the stop feels more mechanical
(i.e., look at your detent assembly), not like hitting the end of a string.
If your bandswitch turns smoothly from one band to the next, is it possible
that somebody disassembled the bandshaft and left out some pieces, or forgot
to tighten things down?

Regards,

Phil Nelson

Phil Nelson wrote:
Is there supposed to be a mechanical stop to keep one from turning the
band change dial too far and screwing it up, or from turning it the wrong
way??


I'm not an SX-28 owner or expert but it looks to me like it's a six
position bandswitch with 60 deg indexing. Why would it need a stop?
It seems it would be a lot better to just allow continous rotation
so you wouldnt have to go back through all the positions when going
from a high band to a low band.

73, Roger

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Remember the USS Liberty (AGTR-5)
http://ussliberty.org/

It seems it would be a lot better to just allow continous rotation
so you wouldnt have to go back through all the positions when going
from a high band to a low band.

Yes, on a simpler radio that doesn't have a moving band pilot lamp or shadow
indicator, you certainly could let the bandswitch rotate 360 degrees in
either direction.

This stop is needed because the SX-28 has two string-driven shadow band
indicators, behind the main tuning and bandspread dials, respectively. The
indicators run on little elevators that can go up in one direction, and down
in the other. When an elevator hits the top floor, there's only one
direction to go, and vice versa :-)

The diagram at http://antiqueradio.org/art/temp/SX28DialStringing.jpg
doesn't show all of the parts and pieces, but it does show the strings,
springs, and major doohickeys that make it work. The crossbar carrying the
main tuner shadow indicator is shown where an arrow points to C. The shadow
indicators are simply bent pieces of flat metal with arrow shapes on the
end, which create shadows by sitting between the pilot lamps and the tuning
dials.

Looking at the diagram, find the main tuner bandshaft, where it says
"connected to main tuning knob." If you turn the main tuning knob
counterclockwise, to move you from a lower band to the next higher band,
that will tighten the two sets of strings and lift the two shadow indicators
upward on their elevators. Turn it clockwise, and it will lower the
elevators one floor. But beyond the top and bottom floor, you can't go any
farther without breaking the strings.

Lest you think this is over-complicated, my Midwest DD-18 (
http://antiqueradio.org/MidwestDD-18.htm ) has gizmos that move a pilot lamp
up and down behind a red/green colored screen to illuminate the chosen bands
on the tuning dial. A "Tunalite" circuit is fed off the AVC line and
darkens/brightens the pilot lamp as you tune into a station. A lamp mask on
the bottom half of the dial changes to illuminate the Wavelength markings
accordingly. The good news is that the whole thing is gear-driven -- no
strings to replace!

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Phil Nelson wrote:


From using my first SX-28, I have to say that the stop feels more
mechanical (i.e., look at your detent assembly), not like hitting the
end of a string. If your bandswitch turns smoothly from one band to
the next, is it possible that somebody disassembled the bandshaft and
left out some pieces, or forgot to tighten things down?

Regards,

Phil Nelson

Phil:
Yeah, it feels like you can turn it past the lower (or upper band) and go
around again and break something. It feels like it's just the cord strength
preventing you from continuing. I don't remember seeing those blocking
washers but I will go inside again and look.

Thanks again Phil, your website has been a huge inspiration and source of
information for work I have done on my 28. Now if I could just get that AVC
working right......

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

In article , "Scott W. Harvey"
writes:

I have seen the "official" tool that was originally used to
attach/remove these rings, and it is a fairly complicated
gizmo....Probably unobtainable unless special-ordered. With that tool,
it's a one-handed job.

If the end tabs of the C-ring each have a hole, then the official tool is
pretty simple. I have a couple of those tools. Unforch, they are "Hong Kong
Hardware" quality tools, and so it's a one-handed job, but very hard on the
throat from the constant profanity needed to "cheer the team" to success.

Maybe you are talking about a larger version of the simple rings, with no tabs,
that hold pot shafts into a pot, for example. Those would require two pliers.
73, Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

In article t, "Phil Nelson"
writes:

This stop is needed because the SX-28 has two string-driven shadow band
indicators, behind the main tuning and bandspread dials, respectively. The
indicators run on little elevators that can go up in one direction, and down
in the other. When an elevator hits the top floor, there's only one
direction to go, and vice versa :-)

The Hammarlund SP-600 has an "elevator" pointer, but it seems to be cam-driven,
so it goes all the way up or donw in a hurry when you roll over the band
selector. Of course, it almost takes two hands to turn the mechanism :-)

BTW, I would want the limit stop detents place up front by the knob, not in the
rear of the bandswitch, so a real gorilla type wouldn't over-torque the switch
shaft.

Just my two cents -- Mike K.



Oscar loves trash, but hates Spam! Delete him to reply to me.