might have been Stereophile from the early 70's or a book I got on HiFi from the same time period: minimizing ground plane potential

need a VOM meter set for 120 VAC

plug the gear in, turn it on

measure the V between the equip chassis or ground lug and the power receptacle ground pin or cover screw...if a symetric plug (not with a larger blade for N) reverse the plug (after power down, etc., lol) and re-measure...orient for the lowest V...do this for all components...

the differences can be significant at times