For older Variax +9V, for JTV +7.4, and have to be very stable and not too high of a current draw.
Caveat,.... everything here on this topic is an at your own risk, since modification like this are not supported by Line 6.
So if something goes wrong with this and it comes to my repair bench, 50/50 chance I'd have to send it back untouched.
As much as I would enjoy the challenge, they pay me to work on Line 6 gear and not a third party who supplies a modification.
Just so you are all aware. That being said, best of luck.