Hetfield uses special Electro Svetlana 6L34 Cs, which are custom made by Vladimir Putin every winter solstice at sundown out of unicorn blood from Abraham Lincolns personal stash.
What I mean by that is that Hetfield has had 6L6s, EL34s, 6550 and maybe now them KT77s in his VH4s, not because they sounded a specific way, but rather because they were reliable at the time.
If your VH4 doesn't sound like Hetfield enough, make sure you down-stroke the s*** out of fresh set of strings on a Les Paul type guitar (set-neck, mahogany) with EMGs (81 or Het-Set). Still not Hetfield enough? Blend in a Mesa Boogie Mark 2/4/5 with scooped out mids (on both EQs) and make sure your cabs are runnin' with V30s.