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Author Topic: Changing power cord on Hallicrafters S-38  (Read 6794 times)
AK4RL
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« on: April 08, 2013, 09:41:16 PM »

I am in the process of refurbishing a nice Hallicrafters S-38 (six tube) and have run into conflicting posts on the web concerning changing the power cord on the radio.  All of the postings mention changing the way the original on/off switch is hooked up to avoid having a "hot" chassis and using a polarized plug.  The conflicting posts concern rather or not to use a three wire cord and tying the neutral green wire to the cabinet.  Some posts do recommend doing this and some posts advise against doing it saying it would create a shock hazard because that would tie the cabinet into the ground system of everything in the house.  I would appreciate some of you experienced rebuilders out their giving me your advice.  TNX and 73, Ray AK4RL
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K2OWK
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« Reply #1 on: April 08, 2013, 09:57:48 PM »

This is not a reply to this question, but I also have the same type of problem. I have restored a National NC-98 and it works perfectly on all bands. If I plug the two prong plug in the wrong way, I get a slight shock from the case when I touch my lamp that is plugged into the same receptacle. I can eliminate this by turning the plug around in the socket. I am supprised at this because the power supply operates through a transformer and should be isolated from the case. I guess I could replace the original plug with a polarized two prong plug, but I would also like to try a three prong plug. So I to am looking for an answer to this
question.

73s

K2OWK
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K1CJS
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« Reply #2 on: April 09, 2013, 04:49:37 AM »

K2OWK--The answer is simple--to a point.  Some of the radio receivers made in the past that have bakelite cases and knobs--that is that have the chassis completely shielded from the user's touch--have one side of the power cord tied to the chassis.  Get and refer to a schematic of the radio in question if you can to determine that.  

The trick is to find out where that tie-in is--if you're unable to get a schematic.  HOWEVER, note that in some of those radios, that connection MUST BE THERE in order for the radio to operate properly.  That is why some advocate leaving the two wire cord alone.  

What has to be done is to meter each side of the power cord--with the switch for the receiver off--to the chassis itself.  If you find a dead short, then look for that connection and temporarily open it.  If there is still some continuity between chassis and the cord connections after that connection is opened, you cannot use a three wire power cord safely, you have to use a two wire cord.  Using a three wire cord in that instance could put 110 volts on the third wire of that house circuit, and if the third wire of that circuit was open anywhere between the outlets and the panel, could make other appliances connected to that circuit with a three wire cord a shock hazard in themselves!

If, on the other hand, you find no continuity at all or can effectively isolate the chassis from both sides of the power line and still have the receiver work properly, you can use a three wire cord safely.  Please note that I'm speaking of 110 volt US connections--220 volt and other foreign electrical systems do vary.

On a lighter note--sometimes it's nice to be an old fart, having the knowledge to help out others!  73!

« Last Edit: April 09, 2013, 05:06:54 AM by K1CJS » Logged
AA4PB
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« Reply #3 on: April 09, 2013, 05:00:40 AM »

Well, connecting the chassis/case to the house electrical grounding system is exactly what codes require of any modern equipment that has an exposed metal case. That way if something does short to the case then the grounding conductor carries the current and the circuit breaker pops. Otherwise if you touch the case with one hand and some other grounded device with the other you could get electrocuted.

The slight shock on the NC-98 may be leakage due to bypass capacitors between the power cord connections and the chassis or it could be capacitive coupling between the transformer winding and the metal core. A polarized plug is a good solution provided, of course, that the outlets in the house are wired correctly. A 3-wire cord is even safer. Get the polarity right and then connect the grounding conductor to the chassis.

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AA4PB
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« Reply #4 on: April 09, 2013, 05:06:57 AM »

Good point about the old radios (often called AC/DC sets) that have the chassis connected directly to one side of the power line. They had no power transformer. I don't think the S-38 is one. At any rate, you wouldn't want to ground the chassis on one of those. In the repair shop we used to have an isolation transformer that we used for testing those "death traps" so we didn't blow up our test equipment by connecting the ground lead to a "hot" chassis.
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AD4U
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« Reply #5 on: April 09, 2013, 11:59:01 AM »

The S-38 receiver IS "one of those".  No power transformer.  At least mine does not have one.

Dick  AD4U
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AK4RL
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« Reply #6 on: April 09, 2013, 09:28:15 PM »

Yes, I am aware that the Hallicrafters S-38 is an AC/DC radio without a transformer and that is why I posted my question.  It does have a metal cabinet and does use rubber grommets to isolate the metal chassis from the metal cabinet.  That is the reason for the question about adding the neutral green wire from a three wire power cord to the metal cabinet to keep it neutral in case there is a leakage.  I am also going to use an isolation transformer.  Have also considered using an old line cord from a hair dryer instead of a three wire since the hair dryer cords are terminated with a GFI plug. I was just checking for suggestions for different options.  TNX and 73, Ray AK4RL
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G3RZP
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« Reply #7 on: April 10, 2013, 01:04:51 AM »

In the S38 situation, I would use a 3 wire cord and plug, with the neutral connected to the isolated chassis and the ground to the metal case.

For the NC98 with its transformer, first check for any capacitors from either side of the AC line to chassis, and check for leakage in them if there are any.  Then again fit a 3 wire cord and plug with the chassis/case grounded. If one side of the AC line is fused, that should be connected to the 'live' side of the AC line input.

Although this is not strictly a true restoration, it does make the equipment safer.
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W9GB
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« Reply #8 on: April 10, 2013, 06:54:30 AM »

Ray -

When restoring the Hallicrafters S-38 models, the SAFETY AC Line Capacitors at the line cord input (AC mains)
http://www.the-s38-guy.com/Page_9.html

Just Radios -
http://www.justradios.com/safetytips.html

http://www.ehow.com/info_8649387_differences-x2-y1-y2-capacitors.html

and rubber grommets should be changed (new) to assure safety and proper operation.
http://www.stanwatkins.com/hals38.htm

How To Stop A Killer : Proper wiring S-38 ON/OFF switch.
http://www.the-s38-guy.com/Page_2.html
« Last Edit: April 10, 2013, 07:02:38 AM by W9GB » Logged
AA4PB
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« Reply #9 on: April 10, 2013, 07:54:43 AM »

Make sure that the neutral and hot sides of your 3-wire plug are correct and that your outlet is wired correctly. Otherwise you could wind up with 120VAC between the chassis and the case. Any shorts mike be max smoke before your household breaker trips.

The absolute safest way to run an AC/DC radio is to use an isolation transformer.
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AA4PB
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« Reply #10 on: April 10, 2013, 08:06:23 AM »

Holly smokes! The S38 as originally configured by Heath is a real "death trap". Not only is one side of the non-polarized plug connected to the chassis but the switch is in the neutral side instead of the hot. Even if you have the plug polarity correct, the chassis becomes hot with 120VAC (thru the tube filaments) when the switch is turned off. The only thing that stands between you and potential serious injury are a few rubber grommets!

I'd definitely use an isolation transformer to power it.
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KD0REQ
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« Reply #11 on: April 10, 2013, 08:38:01 AM »

if the cord is cracked, I would replace it with as close to the original as you can find.  get some X-safety capacitors to replace the ones across the power line to chassis.

and yes, I would use an isolation transformer.  unless you very carefully chase the circuitry down and get a polarized line cord "in right" don't play with that setup.

back in the day, there were no grounds running up to user areas, it was just connecting the antenna and ground that would get you in trouble.  or putting electrical stuff by the sink or in the bathroom.
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W9GB
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Posts: 2626




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« Reply #12 on: April 10, 2013, 11:15:44 AM »

The Hallicrafters S-38 series and many others (All American 5) of that era --
these are AC/DC radios -- and should be used with an AC isolation transformer
on the electronics repair workbench -- FOR YOUR SAFETY.

Hallicrafters Collector
http://www.hallicraftercollector.com/

Phil Nelson and many experienced antique radio (AM/SW) restorers can provide
correct guidance throughout their projects
http://www.antiqueradio.org/halli08.htm
Replacing Capacitors in Old Radios and TVs
http://www.antiqueradio.org/recap.htm

John Schmitz's S-38 restoration (northern Chicago suburbs):
Complete S-38 rebuild from bare chassis
http://www.schmitzhouse.com/Johns_Electronics_08.htm

Bob Piekarz, in LaGrange Park, IL (just down the road).
http://www.radioantiques.com/mall.html

Bob attends most of the antique radio shows and a few hamfests in Chicago area.
http://www.radioantiques.com/index.html
He had these S-38 backs and bottoms made by the same Chicago factory
that made them originally for Hallicrafters (which was HQ in area).

Retro-Tronics offers replacement laser-cut panels, have all Hallicrafters S-38 models.
http://www.retro-tronics.com/sales.php?type=Radio%20Back

I would recommend RadioDaze for parts.
They have replacement Multi-section electrolytic capacitors
in cardboard tube -- if you desire authentic look.
http://www.radiodaze.com/category/355.aspx

Bill Turner (St. Louis area) is also a good source for restoration parts
http://www.dialcover.com/capacitors2.html

Brian Ripley, The Hallicrafters S-38 Guy (Utah)
http://www.the-s38-guy.com/
« Last Edit: April 10, 2013, 11:24:15 AM by W9GB » Logged
W9GB
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Posts: 2626




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« Reply #13 on: April 10, 2013, 03:35:54 PM »

Hallicrafter S-38 Knobs

IF you are missing the knobs, Renovated Radios now has reproduction knobs (KH1, KH2)
as well as rubber feet (FHal-S38) for the Hallicrafters S-38 models.
Scroll down past General Electric knobs.
http://www.renovatedradios.com/parts.html#knobs
« Last Edit: April 10, 2013, 03:39:33 PM by W9GB » Logged
AK4RL
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Posts: 11




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« Reply #14 on: April 10, 2013, 09:47:28 PM »

Thanks everyone for your help.  I am ready to proceed now with my restoration.  I do know for sure that I WILL use an isolation transformer.  Thanks again. Ray AK4RL
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