RCA 8X71-Hum - Printable Version

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+--- Thread: RCA 8X71-Hum (/showthread.php?tid=6800)

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RCA 8X71-Hum - Eric Adams - 06-05-2013

I've got a strange one. All electrolytic and wax caps replaced. Resistors replaced as necessary. Tubes tested. Set aligned on both AM and FM.
The problem is that I get a hum on AM only and only when on a station. In between stations on AM is silent as well as FM.
Any thoughts?

Thanks,
Eric
Schematic:
http://www.nostalgiaair.org/Resources/251/M0015251.htm

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RE: RCA 8X71-Hum - BrendaAnnD - 06-05-2013

Selective hum like this is usually environmental. Try moving the radio to a different area of the house and see if it goes away. My workbench is insane for reception problems. There's some kind of field there that creates a ton of RFI, but if I move the radio under test off of the bench, even just a couple feet, all the noise goes away. Before I discovered this, it nearly drove me mad trying to figure out what was wrong with the radios.

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RE: RCA 8X71-Hum - codefox1 - 06-05-2013

Agree, try moving set around. Most likely a really old dimmer, imported unshielded power supply, shut your bench down completely first.

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RE: RCA 8X71-Hum - Eric Adams - 06-06-2013

Thanks BrendaAnnD, out of the basement and away from my bench the hum is minimized. It's just strange that this is the only radio that I've had this issue with.

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