Summary of Christopher's description of the classic EVH processing chain
Guitar using bridge humbucker
MXR 6-band EQ (frown curve), and MXR Phase 90
100 watt Marshall plexi with Sylvania 6CA7's; powered via Variac to lower (brown-out) the mains voltage from 120 down to 90 VAC.
The head's speaker out impedance control is set at 8 ohms.
Dummy load resistor, adjusted to about 20 ohms
The load resistor is tapped at center
Box with a potentiometer in it and output jack (the output jack is a line-level low-impedance source)
The pot. is adjusted for whatever drive level.
desktop EQ
MXR flanger
Echoplex-EP3
100-200 watt power amp
final power amp by H&H
guitar spks: paralleled 4 cabinets down to 4 ohms to connect it to the final power amp.
EQ and compression at the mixer
Clarifying further:
bridge humbucker
frown EQ
tube amp powered via variac
dummy load
time fx (phaser, flanger, echo) and EQ
final solid-state* power amp
guitar speakers
EQ and compression at the mixer
Taken from.
http://www.amptone.com/eddievanhalenrig.htm