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 Post subject: Hallicrafters S-38C Hum with antenna
PostPosted: Nov Sat 09, 2019 1:06 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 94
Location: Spring Grove, PA
I am working on a S-38C that works well with a 3 ft. wire for an antenna but as soon as I attach a long wire antenna I get a loud hum on all bands. All caps and some resistors have been replaced and all tubes substituted and voltages are correct. The long wire works on all my other receivers, I don't know what to look for next. Any suggestions?
Jeff

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 Post subject: Re: Hallicrafters S-38C Hum with antenna
PostPosted: Nov Sun 10, 2019 3:32 am 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 277
Location: San Jose, Ca.
Hi Jeff, Do you have the antenna connected to #A1? And #A2 connected to G and G to a good ground? You might try that.

Regards, Larry


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 Post subject: Re: Hallicrafters S-38C Hum with antenna
PostPosted: Nov Tue 12, 2019 12:05 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 94
Location: Spring Grove, PA
Larry, Thanks for your suggestion. I turned the radio on with out the antenna connected, I had the link between G an A2. When I touched a grounded wire to the G terminal and drew a small arc and got the same 60 cy. hum. I'm sure the is AC on the antenna circuit, now I know what to look for.
Jeff

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 Post subject: Re: Hallicrafters S-38C Hum with antenna
PostPosted: Nov Tue 12, 2019 2:56 am 
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Joined: Sep Thu 01, 2016 3:56 am
Posts: 277
Location: San Jose, Ca.
Sure thing, Jeff. Some times the plug is not oriented correctly and that can make a difference. The line with the switch should go to electrical common (if it's still wired according to the original schematic). The 2 bypass caps could be causing it, if C24 is weak or C27 is leaky. Also make sure that common is not shorted to chassis. A spark from G to earth can mean the plug is in backwards or C27 is conducting a lot.

Be careful on the shock hazard of these old ac/dc sets.

Have fun.

Regards, Larry


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