Make sure to contact VTL or a VTL dealer... I was considering their amps before I purchased the Quicksilver V4's and decided to not consider VTL after the dealer informed me if you use any tube other than what the factory provides it voids the warranty.
To me personally - part of the joy of tube equipment is rolling tubes to get the best synergy...
To me personally - part of the joy of tube equipment is rolling tubes to get the best synergy...