Need help installing isolation transformer in S-38C
Matt Senecal
understand from looking at it that the chassis carries a potential.
After making some inquiries I have learned that to remove the shock
hazard I need to install an isolation transformer.
While I'm still somewhat ignorant of electronics, I'm fairly handy (I
recently restored an old SX-99 to working condition). But I feel that
working with transformers is a bit out of my league. I would
appreciate some help from someone who has done this before. Basically
what I'd like to know is what kind of transformer to buy (be
specific), and how/where to install it. Any help would be appreciated!
Thanks!
Sparks W4EAS
a external isolation xfmr or use two back to back filiment xfmr's. Then
the S-38 is isolated and you can ground and use in a safe mannor.
Otherwise use a polorized plug. I grew up with ac/dc sets in the 50's
Good luck 73 Sparks W4EAS
Tom Bruhns
the radio; even though S-38's aren't exactly rare, I wouldn't want to
be trying to adding something that would change it from the original.
I'd look for a small (100VA? 150VA?) isolation transformer in a case
with a cord you can plug into the wall, and a socket into which you
can plug the radio. Sorry, I'm not going to get more specific than
that...but you might have a look on, say, the MCM Electronics web site
for such a beast.
However, the chassis should not be "hot" except through a couple of
capacitors, one to each side of the line. The audio output is
transformer-isolated, and the antenna input is link-coupled and
therefore isolated. It _would_ be a good idea to be sure the caps
from the AC line to the chassis are in good condition, and that nobody
has done anything to compromise the isolation otherwise. Admittedly,
the rules for line isolation are now rather more strict than they were
in 1950 or whenever it was built, so an isolation transformer could
serve as an added measure of insurance. But you should be able to
_ground_ the chassis, also, to provide protection. (Expect the caps
would trip a GFCI...)
Cheers,
Tom
msen...@logicon.com (Matt Senecal) wrote in message news:<50ecc828.02060...@posting.google.com>...
eh...@nospambellatlantic.net
What you are describing is an isolation transformer. You plug
the transformer into the wall receptacle - and you plug the radio
into the receptacle on the transformer.
Specs: input 120 VAC, output 120VAC. Current - that depends
on how much current the SX99 needs. The isolation transformer
needs to supply at least as much current as the SX99 is rated
for. Bring money - it won't be a 5 dollar item.
Be sure it is an *isolation* transformer. I saw one advertised
somewhere that was an autotransformer, not an isolation
transformer. You do not want an autotransformer.
There is another way to provide the safety you want, and
it is a lot cheaper. You can install a 3 wire cord and
plug, and use the SX99 only with properly grounded
receptacles. The green ground wire in the 3 wire cable
connects to the chassis. The white wire in the cord
is also electrically connected to the chassis through
existing circuitry. You will need to have someone
who knows how tell you which wire (white and black)
connects where.
Sven Franklyn Weil
eh...@nospambellatlantic.net wrote:
> receptacles. The green ground wire in the 3 wire cable
> connects to the chassis. The white wire in the cord
> is also electrically connected to the chassis through
> existing circuitry. You will need to have someone
> who knows how tell you which wire (white and black)
> connects where.
One little piece of information.
You may encounter some three-conductor
power cords
with the following colored conductors: Brown, Blue, Green/Yellow
This is the new color coding that was adopted a couple of years ago by ISO
or some international standards body like that. Europe has used it for
years and some imported power cords are actually coded like this. The
USA hasn't quite adopted it yet, so it's not likely you'll find it in a
hardware store (yet).
Anyway here's the break down:
Live (Hot): Black or Brown (goes to the narrow pin on a polarized plug)
Netrual: White or Blue (goes to the wide pin on a polarized plug)
Ground (Earth): Green or Green/Yellow
--
Sven
Roy Lewallen
Tom Bruhns wrote:
> . . . But you should be able to
> _ground_ the chassis, also, to provide protection. (Expect the caps
> would trip a GFCI...)
I wouldn't do that! Those capacitors can carry quite a bit of current.
My first receiver was an S-38D, which I once grounded. When I turned on
the power, an arc formed at the power switch, and it continued until I
raced downstairs and frantically threw all the house's circuit breakers.
(The arc was between me and the plug.) This made a big impression on my
parents, who never forgot it. I didn't either. And I'm sure you won't,
either, if it happens to you.
Use that isolation transformer!
Roy Lewallen, W7EL
Roger Brown
it was a cheap way to do things back then. They are not, however,
particularly unsafe with normal precautions. The S-38 was not a serious
communications receiver anyway (more geared to SWL'ing). Used for causual
listening - I would think it would be fine the way it is. As someone else
stated - many of us grew up with AC/DC sets and they hardly ever caused any
problems.
R.G. Brown, NL7FP
.Bill :-)
The S-38 I had, I forget which model, had the chassis isolated from the
metal cabinet via rubber mountings. So it wasn't an automatic killer
<G>.
If the rig in question also has them, restoring those mounts should be
the first order of business.
-Bill
Williams
the Almighty for their deliverance.
Rick
>> AC/DC's are no problem. I don't understand why you would bother.
When I was a kid in the 50's, we had a 78 rpm record player with a
metal arm on it. We'd use it on the back porch which had a concrete
floor, and we kids were always barefoot.
Sometimes we would grab that arm and get the s___ shocked out of us.
We figured out (we didn't know why) but if you put the plug in the
wall the other way it wouldn't shock us.
Geniuses we were.
Ron Banks
usually a lot of them on ebay as IT departments upgrade their equipment.
Battery condition wouldn't be an issue as isolation is your only need.
Another source of transformers is automotive battery chargers and Malibu
light power supplies. I see a lot of these at garage sales. Hooking two
reasonably matched transformers back to back as previously mentioned would
get you an inexpensive isolation solution for your bench.
I once converted an S-38E (bought without tubes) using the power transformer
from a junk audio generator. I used a silicon diode to replace the
rectifier tube and rewired the other sockets for 6 volt filament tubes. It
worked fine. Just make sure the 6.3 volt winding will power the remaining 4
tubes.
Regards,
Ron Banks
"Matt Senecal" <msen...@logicon.com> wrote in message
news:50ecc828.02060...@posting.google.com...
Dave Holford
I had exactly the same problem with an S-53.
After checking around with some people with experience I removed the 2
wire power cord and the two capacitors from line to chasis.
I then installed a three wire cord and connected the ground wire (green)
to the chasis. I did not install any capacitors from line to ground.
Works like a charm! And it is safe!
This fix works just fine and involves an absolute minimum of work and
cost. However, for the purists, it does involve modifying the radio;
even though it is a minor mod and easily reversed if you prefer to live
dangerously.
Still wonder about the guy I bought it from since he had it sitting on a
metal radiator (one of those old hot water things which I assume would
be grounded). Maybe that's why I got such a good price.
Good luck
Dave VE3HLU
w9gb
of the S-38 model)
S-38 Schematic
http://www.nostalgiaair.org/Riders/showinfo.asp?PATH=HAL&IMG=_HAL_15-59.gif&
INF=S38
This was discussed at some length in December 2001 on the boatanchors forum
[earlier post]
----------------------------------------------------------------------------
Some useful links for further research (and ideas):
http://antiqueradio.org/halli08.htm
Here is an excellent web site for S-38 restoration notes. He even
demonstrates how he "recast" the knobs and notes that the rubber isolators
are absolutely necessary for a SAFE chassis (AC/DC) with the S-38.
http://www.concentric.net/~Stwradio/hals38.htm
http://www.concentric.net/~Stwradio/hals38.htm#Hallicrafters%20S-38%20Restor
ation
and more S-38 links !!
http://www.concentric.net/~Stwradio/hals38.htm#S-38%20Links
add an S-meter
http://antiqueradio.org/art/smeter03.jpg
http://antiqueradio.org/smeter.htm
The Hallicrafters Collectors' Web Site:
http://www.w9wze.org/
Here were my notes on the internal isolation "torroid transformer"
discussion for the S-38:
The UK audio designers gave me an idea to look at a toroidal transformer, as
a possible isolation transformer under the S-38 chassis, instead of the
traditional external isolation transformer Stancor P6410 (50 VA rating).
I received and e-mail for Brian Gladstone, Director of Engineering at
Plitron Corporation in Canada
http://www.plitron.com
BTW S-38 draws 30 watts at 110 Volt according to specs
Plitron makes Toroidal transformers, and by my measurements one of their 50
VA units will slip right in under the S-38 chassis. You can mount it with
one screw (use the hole for the old multi-section electrolytic).
You can select from a couple of secondary voltage (110, 117 vac ) models.
Presto, same $ 35.00 USD price (thanks to CDN / USD exchange rates) as a
separate Stancor P6410 (50 VA rating), without hauling around an external
unit.
The AC power cord (on this particular unit under discussion) must be changed
to a polarized plug &
fused as well as the rubber isolation mounts repaired/replaced. Then you
will again have a SAFE chassis around children. A power switch, if desired,
could be mounted on the back chassis (or rework the receive/standby switch
on front panel).
I e-mailed to Bob Eslinger, KR1U and he would be interested in hearing from
S-38 restorers who are using this approach Torroid transformers, due to
their low profile, might be a solution for some of his antique radio
restoration clients wishing to maintain appearance, without the external
isolation transformer.
-------------------------------
[end of earlier post]
Greg
w9gb
"Matt Senecal" <msen...@logicon.com> wrote in message
news:50ecc828.02060...@posting.google.com...
Tom Bruhns
Wow, that sounds like a product liability issue for Hallicrafters.
Guess that wasn't such a big issue back when we were growing up.
Perhaps it's a good thing you DID have the chassis grounded, so it
wasn't YOU that ended up completing the circuit back to earth. I'm
truly thankful for the contributions you've made to the ham community
since then, Roy. :-)
Fortunately, I never had such a problem with mine like that. Of
course, an isolation transformer won't necessarily protect against
such arcs, and it's also a good idea to have an appropriately rated
fuse (an amp or so?) in the circuit. So, for the OP...get an
isolation transformer that also has a fuse. The schematic I looked at
didn't show a fuse in the radio. I wonder what one of our product
safety engineers would say if he looked at an S-38 or similar radio
today!
Cheers,
Tom
Uncle Peter
and metal cabinet must be replaced with a UL approved line duty bypass
capacitor of .05 mfd or less.
Pete
"w9gb" <gregor...@attbi.com> wrote in message
news:WSMM8.224090$Po6.3...@rwcrnsc52.ops.asp.att.net...
> /hals38.htm#S-38%20Links
>
at > The AC power cord (on this particular unit under discussion) must be
Uncle Peter
".Bill :-)" <TheRea...@netscape.net> wrote in message
news:3D0182A1...@netscape.net...
the outer steel cabinet. It may not have been a serious problem back
then, but after 50 years most paper caps have developed serious
leakage and should be replaced, especially those that can place a
user in harm's way.
Pete
Phil Nelson
he has allowed me to publish at http://antiqueradio.org/safety.htm .
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html
P.S. Sorry if this was mentioned earlier in this thread -- I recently had to
reformat the hard disk on my computer and lost all history.