Dehumming clavinet recording

Hey hey,
I have a clavinet recording - if you don't know it: say electric guitar. It 
comes with a very prominent 50Hz hum.

I have more or less successfully tried a chain of 50-150Hz highpass filter, 
depending on the track, followed by the C* NoiseGate (CAPS plugins ID 2602), 
sometimes followed by a volume automation.

This sort of works, there's enough ground hum left while it's playing - some 
more EQ can help here.

Thing is: this process is very time intensive, boring and for all that simply 
passable and not great. Does anyone have a different idea? A LADSPA, perhaps 
even a free LV2 plugin, Csound or Faust thing or a standalone commandline 
utility?

Best wishes and thanks,

Jeanette

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