OK...just sharing my thoughts here...
So I got the head, tried it out, did the JP1 mod (which did indeed brighten up the tone) and tried out a few different pre tubes. Don't have any power tubes on hand. :(
Tried a Mullard 12AT7, RCA 12AT7 blackplate, RCA 12AT7 grey, Shuguang 12AX7, Siemens...