[R-390] query re ground loop

[Tisha Hayes]

With the switchover to a two prong connector you have pretty much narrowed
it down to a ground loop.

In the circuit box the neutral (white) and ground (bare or green) wires will
be bonded together. It they are also bonded together in the radio chassis it
is a ground loop but not one that I would have expected to be noticeable.

Ideally the hot and neutral conductor in the radio should go to the line
filter, power switch and power transformer only. The ground wire should go
to the chassis.

If this problem recently appeared you may have "something" in the receiver
that is leaking to chassis ground. Since you are getting by with a two wire
adapter the radio can function but it still is not a good thing. Try to use
a voltmeter to measure the potential between chassis ground and the
grounding pin at the outlet.

I will give an example on why you do not want to let this go on unaddressed;
My Dell laptop power supply was attached to the wall when I took a lightning
strike at the house. The laptop was not attached at the time and when I
plugged it in things worked fine. One unpleasant experience was that the
plug to my laptop suddenly had a partial AC potential on the barrel of the
connector. It was not an issue unless I swapped laptops from my personal
D800 (plastic case) to my work laptop with a metal case. If I was using the
laptop in my "lap" (on bare legs) it would give me an unpleasant shock.

Being naturally lazy I put it low on my priority list of things to replace.
I just learned to use something as an insulator between leg and laptop.

The downside was that the problem in the power supply did not get better.
Finally this last fall it went into a full fault and put 120 VAC on the
laptop and blew out the motherboard on the laptop when I plugged into an
external monitor.

I suggest trying to figure out exactly what is causing the hum on the radio
before you (or your child, spouse, dog, etc..) completes the circuit to
ground.

-- 
Ms. Tisha Hayes/ AA4HA
----------------
"I'll be a diode, cathode, electrode
Overload, generator, oscillator
Make a circuit with me." -- The Polecats