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a/c power cord polarity question

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Post by foxcovert on Fri Jun 17, 2011 4:33 pm

I'm working on a westinghouse h130. There is a note on the alignment page:

"When the receiver is operated on 120 volts......a slight hum may be heard if the power plug is inserted so that the hot side of the supply line is connected nearest to the chassis". It goes on to instruct "reverse the plug to eliminate the hum."

My question: what do they mean by "nearest to the chassis"? I'm going to install a new power cord with a 2 prong, polarized plug. I've read that the "hot" side of the polarized plug should be wired to the on/off switch. Would that still be true for this radio?

The a/c line on one leg is connected to the on/off/volume switch, the heater circuit and to the converter tube; on the other leg it connects to the rectifier tube then onto the output transformer.

I'm a newbie.....thanks for your help!

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Post by Bill Cahill on Fri Jun 17, 2011 4:56 pm

That would be the side of B-. Sometimes goes directly to chassis, other times goes through a capacitor, often a .05 mf cap.
That is the side nearest to the chassis, or, ground potential.
Bill Cahill

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Post by foxcovert on Fri Jun 17, 2011 5:04 pm

Thanks. Much appreciated.

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Post by Brig on Mon Feb 06, 2012 7:18 pm

foxcovert wrote:I'm working on a westinghouse h130. There is a note on the alignment page:

"When the receiver is operated on 120 volts......a slight hum may be heard if the power plug is inserted so that the hot side of the supply line is connected nearest to the chassis". It goes on to instruct "reverse the plug to eliminate the hum."

My question: what do they mean by "nearest to the chassis"? I'm going to install a new power cord with a 2 prong, polarized plug. I've read that the "hot" side of the polarized plug should be wired to the on/off switch. Would that still be true for this radio?

By properly wiring the "hot" side of a polarized line cord to the switch of an AC-DC receiver, you make the chassis safe if touched and, as a bonus, can attach an external ground to the chassis for possibly improved reception. I make this essential improvement to every AC-DC receiver I acquire.

The a/c line on one leg is connected to the on/off/volume switch, the heater circuit and to the converter tube; on the other leg it connects to the rectifier tube then onto the output transformer.

I'm a newbie.....thanks for your help!

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Post by Bill Cahill on Mon Feb 06, 2012 9:24 pm

Do not ground the chassis on an ac-dc set. A short could occurr, and, cause trouble. At the least, it makes it a bigger shock hazzard.
The chassis on most ac dc sets. has a capacitor running from chassis to B-, which is supposed to be the lowest side of the ac line.
Be very careful with these types of radios. They are a shock hazzard, at best. Keep one hand in your pocket for safety.
Never stand on a damp, or, wet florr, and, never in even stockined feet. Always wear shoes when handling chassis.
Stay away from all grounds, including plumbing, and, don't, repeat, don't use a ground wire.
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