I broke down and ordered a complete set of matched pre-amp tubes (5) Svetlana 12Ax7's and matched premium 7189 power amp tubes ( EL-84 class) from http://www.thetubestore.com/Tubes/EL84-6BQ5-Tube-Types/Preferred-Series-7189-Premium-EL84 . for my trusty Mesa/Boogie Studio .22 I've had since '89 . All I can say is WOW !!! I'd been running Mesa's best , and these are noticebally quiter and very Hi-FI . I'd strongly recommend them .