a/c power cord polarity question

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!

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

Thanks. Much appreciated.

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.
Welcome to the forums.
Bill Cahill

I'm now going to quote from a book now quite hard to find but an excellent treatise. It's Rapid Radio Repairby G. Warren Heath, first published in 1959 by TAB Books, last printed in 1973. From pp. 92-94: "In transformerless radios one side of the circuit is directly connected to one side of the line. In much of such equipment, tghe metal chassis on which the components are mounted is part of that circuit--in some others a single lead or bus--usually forming the negative-dc lead of the circuit As well--is connected directly to the chassis through a small capacitor shunted by a large resistance, to increase operational stability.

"A simple form of protection is to use two-prong polarized plugs. You may not be aware of it but the chances are 10 to 1 that the receptacle on the wall. . .is polarized--one slot is wider than the other. The wide slot is connected to the grounded wire of the electric system (or should be). Used with a polarized plug (one prong larger than the other) this would seem to mean that a radio set could be so hooked up that that the chassis would stay at ground potential. But one serious drawback stands in the way of this easy-looking solution.

"The polarized plug WOULD make a chassis safe IF IT were connected to the grounded side of the line at all times. Unfortunately, most small radio receivers have the line switch BETWEEN THE SET OR CHASSIS GROUND AND THE LINE. When the switch is opened, the connection to earth is broken and the whole set becomes hot. . . .If the switch is on the other side of the line. . .so that the hot lead is disconnected when the switch is turned off, the equipment remains connected to ground and is [always] safe.

"Another suggestion is that an isolation transformer be used. This would presumably make the set safe, but is an awkward and expensive way. The suggestion presumes that the sets are inherently unsafe, which is not the case."

I've made this easy modification to at least 25 units (several for customers) and have never had a safety problem. Also, I have in my collection a few AC-DC sets for which the manufacturer provided for an external ground connection (Stromberg-Carlson 225-H is one example). I agree with Heath above that these sets are maligned too frequently; properly modified they can be excellent, inexpensive performers.

By the way if anyone does not know how to determine if his home electric system is polarized, he should hire a licensed electrician to determine it.