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Hum with phonograph only?? - Printable Version

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Hum with phonograph only?? - ODPILOT - 06-02-2013

   
6/2/13
Done restoring a 53-1750 Radio/Phono console. Replaced ALL caps and most resistors. I also replaced the cap underneath the phonograph where all the guts are. When I turn the selector knob to phono, I get a pretty good buzz which is not present on the radio band(s). Gets even worse when I put my hand near the needle arm. It does play the records fine (also put in new belt and idler wheel) --but has this background buzz/hum while in phono mode. Maybe it's just interference being picked up from electric devices in the house?? Not sure. Any ideas??
Thanks,
Mike

RE: Hum with phonograph only?? - morzh - 06-02-2013

Grounding. Check your wires from the adapter, the shield and whether the chassis is connected to the radio's chassis and how.

I do not know how it should be (I have no sch) but this is typicsally the reason - the Grounds and Ground loops.

meantime you can describe how the turn table is connected to the radio. In all details.

RE: Hum with phonograph only?? - Radioroslyn - 06-03-2013

Hi Od
Do you have to turn up the phonograph pretty loud to hear it?? Short of a ground loop you may have a weak cartridge.
Terry

RE: Hum with phonograph only?? - ODPILOT - 06-03-2013

As far as I can tell, there are no grounding problems. Everything is connected and I've check all the new caps to make sure connections are solid.

As far as turning up the volume to hear the record better -- I would have to say yes. I probably due to have to give it some power to hear it better.
It does have a brand new needle but the cartridge is the old one. When I put my hand near the cartridge/needle, the humming gets louder.

I'm not sure if the cartridges are readily available for this 53-1750. I would have to check.

Mike

RE: Hum with phonograph only?? - Chuck Schwark - 06-04-2013

Sure sounds like the tone arm and/or cartridge body are not grounded.
Corrosion in cart mounting screws, tone arm pivots?? Missing ground wire
from tone arm down thru the "hole" to turntable frame?

Just typing out loud...

Chuck

RE: Hum with phonograph only?? - morzh - 06-04-2013

I also think so. Well-grounded adaptors should not produce hum even at large volume setting. Especially if you move your hand close to it.

PS. I do not know much about those but...by chance, they did not rely on the shield being also the GND signal conductor, did they? That would not be good.

RE: Hum with phonograph only?? - ODPILOT - 06-04-2013

6/4/13 Thanks people -- OK I will look more closely at the needle cartridge and arm and grounding wires. I'll have to unscrew the phonograph and take it back out . What a pain in the neck !! It's very hard to get access to the arm while the phongraph is installed in the draw. Also, looks like EV (Electrovoice) makes a repro cartridge for this phonograph.
Cheers,
Mike

RE: Hum with phonograph only?? - GarySP - 06-04-2013

I concur with the rest of the comments. Double check the tonearm and cartridge ground before spending money on a new cartridge. Nothing worse than dropping money just to find out it didn't cure a thing. Take care. Gary

RE: Hum with phonograph only?? - codefox1 - 06-05-2013

Work backwards or fowards if you prefer shorting (1st grid) or audio signal only from the volume control backwards to the cartridge. Wherever you wind up, it's the trouble point. Just don't short out any B+ voltages.

Best guess 1. bad cartridge, 2. bad shield. Pray for #2.