[Hallicrafters] Hum in FPM 300

[Harvey]

I have been  looking here to find an answer for my hum.  The rig was working fine when I recently picked it up from the previous owner.  Now when I try to tune it up on any of the bands there is a hum that reads about 5-6 on the S meter.

Would that be reversed polarity?  The previous owner was running it off of an inverter to 110 VAC from 12 VDC.  I really would like to get this rig up so that I can listen in on the net and to practice some morse code.

Thanks for all of the help.

Harvey
KB7ZMG
Medford, OR 
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