Checking out a modified (by another company) MB-3045 monoblock and
there is a slight 120hz hum at the speaker.

Checked circuitry with a scope and the input of one output tube has low 120hz signal,
but that signal is still 10+ times higher amplitude than the 120hz signal to the
other output tube input.

Of course, the power supplies measure virtually zero 120hz (50mv/division on the
scope), and being common to both plates and cathodes of each stage, the supplies
should not be the cause.

Any thoughts as to the cause is most welcome.

Thanks for time and efforts.

pos