On one leg or two legs?

Just did it again- no ICs connected, plugs in the inputs- same hum.
01-31-09: Maril555

Maril555,
By chance do you have a multimeter? If so why not try a plug polarity orientation test for each power amp.

To do the test you will need to trim the polarized plug blade on one of the ground cheaters. A pair of tin snips will do the job. Trim it down to match the non- polarized blade. The idea is so you will be able to plug the cheater either way into the wall receptacle.

For the test, no ics, just the plugs on the inputs of the amps.

Plug the modified ground cheater in the 120v recept the normal way and plug the amp into the cheater.

Turn on the amp.

Set the multimeter to AC volts.

Insert one test probe of the meter into the U shaped ground hole of the recept making good contact with the metal ground contact.

Touch the other probe of the meter to the chassis of the power amp. If you have to, remove a screw on the back somewhere to make a good contact to bare metal.

Note the AC reading..... write it down.

Now turn off the amp..... You will need to wait awhile before you can turn the amp back on for the rest of the test, so just preform the same test on the other amp next.
Just follow the same procedure for the second amp. Again make note of the voltage measurement.

Now go back to the first power amp. This time you want to flip the cheater plug 180* in the recept.

Turn on the power amp.

Again measure the AC voltage from the ground of the recept and the chassis of the amp.
Note the voltage.

The lower of the two voltage measurements is the correct plug orientation polarity.

Repeat the test for the other amp.

Big question now is the hum less for each amp?

If the preamp has a 3 wire plug you might want to check it as well. Make sure all ics are disconnected from the inputs as well as the outputs.
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Jea48,
First to answer your question- If I understood you correctly, you are asking if the hum is less with ICs disconnected?-
No, it is not.
Can I use a polarity checker, kind they sell in Home Depot, to accomplish the same, unless you meant to do this test for a purpose, other, than to check polarity of each receptacle?
I cannot understand one thing, though- how come the hum is louder in one channel???

Can I use a polarity checker, kind they sell in Home Depot, to accomplish the same, unless you meant to do this test for a purpose, other, than to check polarity of each receptacle?
I cannot understand one thing, though- how come the hum is louder in one channel???

No, you will not be checking if the receptacle polarity is correct.

You will be checking if the 120V AC polarity orientation of the primary of the power transformer of the power amps is correct.

If you do not have a multimeter you might just try a simple listening test. Same set up with the ground cheater just listen for any difference..... The meter is the best sure way though.

You can pick up a decent one at Rat Shack for around 50 bucks....
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Got you,
Here are the measurements.
Meter set at ACV 50
Left amp: Right amp:
Right cheater plug: 38 37
Reversed: 33 30

So, what's the verdict?

The answer to the big question- no, hum is the same after AC plug is reversed