how to reduce hum with 2 resistors. simple and easy way for tube audio amplifiers. EL34 KT88 6L6 - YouTube
Stop Unwanted Buzzing or Humming From Sound Systems and PA - YouTube
Amazon.com: Golvery Ground Loop Noise Isolator, Auido Humming Hissing Buzzing Noise Filter Eliminator for Car Audio, Home, PC Stereo System with 3.5mm or RCA Aux Jack : Electronics