Thanks Robbie, for information on the varistor.  I guess my main concern
is leaving these old pianos with original wiring plugged into a household
receptacle when not in use.

My Seeburg has all original wire (most of it has mildew on it).  I
try to disconnect the piano when I am not using it or away from home.
However, I know others that have left their old pianos with original
wiring connected to an electrical receptacle for years, and no problems.
Yet I have second thoughts about this practice.

Also I have seen a few wires "sizzle" under very humid conditions, such as
out-door receptacles, and wondered if electric pianos might do the same
thing under very humid conditions.  (Our humidity today is 86%!)

Bruce Clark