Ask ARC. I don't own your amp, but I did own a predecessor. They used to have reservations about using KT88's in their amps in general. I believe because they didn't want to have to pay for damages caused by poor replacement tube selection by customers when the amp was still under warranty. Part of that had, I believe, to do with KT88 reliability and the consequent damage that poor ones could cause when used in their amps, but part of it could have to do with the design criteria of the amp. Some high power amps can eat less than very rugged KT88's. I've got a couple of those. FWIW.