I'm not well versed on the subject, But I wonder if it would help to drive one channel of your scope through a well filtered say 6V transformer,
then the other channel connected to the ac line with a 20 to 1 resistive divider. Now invert one channel and use the variable attenuation knob to cancel all
of the 60Hz signal. Now what is on the scope is the difference between the two signals, that is the noise. You can change the attenuation of both channels to get the gain you need to see the noise.
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? To push this a little further, put the 6V transformer in a box with the Resistive divider, but put a pot as one resistor ( or more complex fine adjust), Connect these out of phase to cancel all but the noise and look at the output with a single scope channel. Then adjust the attenuation to see the noise better. May need to fiddle with the fine tune to cancel all the 60Hz ac.
????????????????????????????????????????????????????? Mikek
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Safety is another issue I'm aware of but, I did use a scope with an open ground plugged into a isolation transformer for 10 years while repairing VCRs in the 80s.
