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 Post subject: ground loop problem with mono hifi tuner
PostPosted: Mar Tue 05, 2019 10:03 pm 
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Joined: Mar Tue 05, 2019 9:58 pm
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A neighbor gave me a Sherwood S-2000II.

When I connect it to an amplifier it creates a loud AC hum in the amplifier.
I looked at a troubleshooting page and have determined it is a ground loop problem. but they did not indicate how to fix the problem.
I reversed the a/c plug, but that did not good, hum is there no matter which way I plug in the power cord.

Any Ideas? Maybe connecting a ground wire from the tuner to the amp?

thanks

john


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Wed 06, 2019 1:11 am 
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Joined: Jan Tue 31, 2012 1:55 am
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Location: Mountains of Mourne. Ireland.
Hello John.

Touch wood... I've never had any trouble with ground loops... :)


These can be found on ebay for ten bucks or less.

Image
http://www.antiqueradios.com/forums/vie ... 9&t=258922

Rear of package: https://i.ebayimg.com/images/g/i~sAAOSw ... -l1600.jpg
eBay item number: 233154058681


Greg.


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Wed 06, 2019 2:10 am 
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Quote:
Any Ideas? Maybe connecting a ground wire from the tuner to the amp?

That won't work because the shield conductor of the RCA cable is already connecting the "ground" between the two units.

The device Greg above should work. If either or both units have been modified with 3-prong power plug, "lift" one ground with an adaptor like this may work.


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Wed 06, 2019 2:52 am 
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Maybe the tuner chassis is hot due to a defective capacitor. I don't know about the S-2000 II version but in the S2000 there's is a 5 nF cap between the incoming AC line and chassis (also rightly called "death cap"). If such a cap is present in your tuner cut it out completely and don't replace it.

Another thing to check: what kind of antenna are you using ? Is the hum still present when you completely disconnect the antenna ?


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Wed 06, 2019 3:29 am 
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Location: Mountains of Mourne. Ireland.
5nF (nanofarad) Capacitor mentioned by Tubologic.
Image
Sherwood S-2000II... :shock:


Service manual here...
https://elektrotanya.com/sherwood_s-200 ... nload.html

On the elektrotanya website...
Wait for the ...processing... notice to change to Get Manual ←it takes a while!


Greg.


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Wed 06, 2019 4:35 pm 
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maxxkatt wrote:
When I connect it to an amplifier it creates a loud AC hum in the amplifier.
Can you control the level of the hum with the volume control on the amp or is it at a fixed volume regardless of the control's setting? Can you hear stations along with the hum?

If it is a controlled hum there could be an open shield connection at one of the RCA plugs or at the jack, itself. Try connecting a separate ground wire to test for this. Otherwise, you may have one or more bad filter caps in the tuner's power supply.

If it is a fixed level hum, some of the other suggestions may apply.

Dave


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Wed 06, 2019 5:41 pm 
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Remove the 6X5 tube in the tuner, then it should be silent. If that gets rid of the hum, you actually have bad filter capacitors, not a ground loop.


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Fri 08, 2019 5:22 pm 
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The Capehart 400 series, at least in my 413N, has a 10 ohm resistor in the chassis ground circuit between the tuner chassis and the power supply/amplifier chassis to eliminate a possible ground loop. This might work for you. Just a suggestion. Good luck! :)

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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Mar Fri 08, 2019 6:15 pm 
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Location: Boston, MA USA
If both the tuner and amplifier have power transformers then it is unlikely your problem is due to a ground loop. More likely is absence of a ground.

-David


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Apr Thu 11, 2019 2:40 am 
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You might try adding a 39 ohm or so (not critical value) resistor in the audio cable ground line. It stops inductive currents in the shield that can cause hum.
Cheers,
Roger

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Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Apr Thu 11, 2019 10:44 pm 
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Joined: Aug Tue 04, 2009 2:15 pm
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Location: Elmira, NY
Double check your audio patch cable. I just dealt with this connecting my tv to my stereo receiver. The RCA plugs and jacks oxidized and the shields were ineffective. I sprayed de-oxit in the jacks and applied anti -oxidizer compound to the plugs.


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Apr Mon 15, 2019 9:41 pm 
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Y2KEDDIE wrote:
Double check your audio patch cable. I just dealt with this connecting my tv to my stereo receiver. The RCA plugs and jacks oxidized and the shields were ineffective. I sprayed de-oxit in the jacks and applied anti -oxidizer compound to the plugs.
Good move, but it may leave an even more effective hum loop! I recently fixed a weird hum between my cable TV audio and the separate stereo system... it was from the RF cable shield to the set-top box! I added 39 ohms to the RF cable shield... hum fixed!
Cheers,
Roger

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Thornhill, Ontario
Ontario Vintage Radio Assoc. http://www.ovra.ca


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 Post subject: Re: ground loop problem with mono hifi tuner
PostPosted: Apr Mon 15, 2019 9:52 pm 
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BikenSwim wrote:
Remove the 6X5 tube in the tuner, then it should be silent. If that gets rid of the hum, you actually have bad filter capacitors, not a ground loop.

This is the easiest check of what is very often the cause of hum. At least doing this eliminates the filters as suspects.

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