Back in the 60s/70s most English folk set them either all tones at max (10) vols around 5-7, or all tones at noon except presence down at 2 (Thin Lizzie). Bass at zero in the studio was quite common too...
I'm a "all tones at max" vol at 6-7 myself, occasionally presence at zero when I have to use the PPIMV I have on mine..... runing TMB knobs equally seems to yield the best touch response on all four holers, JMT45, JMT45/100s too... ( I run JTM45s vols 7-8 or 10)
EDIT they sound "loverly" turned right down even without a MV at home for clean noodling and a fuzz face will give you JIMI as quiet as you like... lot of nonsense talked about this on TGP...
No kidding, so many posters parrot this crap. Totally usable all up and down the volume spectrum. 100 watt plexi has one of the best clean tones ever...ask SRV.
And also the 1987 50 watt is nothing like the 1959. They break up way too fast and are have nowhere near the clean tones. I've owned many of each over the years.
Pretty sure SRV used a 200 watt Marshall Major. But either way, yeah, plexis sound great clean too. It's just not the "Marshall sound" people think of right away. But man, they do sound amazing cranked!
Every amp is slightly different, use the technique of eq at 0 then bring in until you notice a sonic difference, each knob. Note where this takes place and adjust from there.
Don't use EVs, it will be the loudest thing you ever hear!