A little detour but, no matter how you slice it, all of these PPIMV designs simply turn the fixed PI output resistors (bias splitters, aka grid leak resistors) into a variable resistor (pot). This is the reason some might notice certain hot-rodded amps sound louder or fuller or more meaty than another. For example, older Ceriatone Chupacabras used 87K, newer ones use 110K, the Yeti uses 120K, Fortin uses 150K, some Marshalls with 6550s used 150K, EL34s were 220K, etc. Care should be used when messing with these resistor values and/or using a PPIMV because the total resistance the tube grid can handle should not be exceeded. This INCLUDES any grid stoppers. Although I doubt anybody is gonna go highter than 220K + grid stoppers.
