Wrong amp!! Series IV X 100B running 6l6's was NOT the X Amp Vai was running at that time! That amp was the same amp I have a Series III X 100B Hot Rod Mod likely running EL 34's. I have owned a 100 in the past and own a 50 now both mine were EL 34 amps. Totally different beast!
The factory Hot Rod Mod amps were different and with the HRM engaged think big time modded Marshall tones and face melting gain levels!!
My X50 Hot Rod Mod head no effects gain at about 3.