I've just seen Vai's auction on ebay. He sells his amp that he had used on David Lee Roth's "Eat'em and Smile" album.
The official auction page says;
Ebay auction number; 290683338989 and reserve price is $4550...For sale: Steve Vai’s Marshall 100 watt 4 input JMP Plexi & matching “white face” 4×12 cabinets used on David Lee Roth’s “Eat Em and Smile” record and the 1986-1988 David Lee Roth tour.The 100 watt Marshall JMP was given to Ted Templeman by Steve Stevens during the NYC recording sessions for “Eat Em and Smile.” The amp was then modded to Steve’s liking by Lee Jackson, famous for performing sought after custom modifications to Marshall amplifiers for top artists in the 1980′s and 1990′s. It was Steve's main amp for the "Eat Em and Smile"sessions and used on the entire David Lee Roth tour. The 100 watt plexi head features an extra gain stage, frequency adjust control, effects loop & master volume. The head has been well maintained in Los Angeles and features matching Drake transformers, KT88 quad-matched power tubes & hand-selected pre-amp tubes to Steve’s liking.The twin 4×12 cabinets are outfitted with Celestion Vintage 30 speakers made in Ipswich, England. Both cabinets bear Steve’s signature, certification & are in perfect working order. This is your chance to bid on a historical piece of equipment used by a legendary performer in their international breakthrough role. This is an official Vai.com auction. All questions will be answered as promptly as possible. A portion of the proceeds will go to he Make-a-noise fund, a 501.3c which provides musical instruments to cultivate and preserve musical awareness, development, and education.