While the pins fit, the amp doesn't have big enough transformers to get either the full power or best sound quality out of the KT150, so don't be surprised if you find that the stock tubes (EL34 type) sound better than the KT150s, because they are getting all the juice they need to sound their best while KT150 gets half of what it wants and would easily saturate the OPT if allowed to make full power. Hopefully the KT150s will still make better tone and presence than your stock tubes, but usually tubes sounds best when powered closer to their max ratings. Kevin Deal (PrimaLuna importer) is a master marketer but he's not a chister, so I'm sure it will sound good if he says try KT150. I look forward to your take as I'm intrigued by these big tubes also. The little amp will be dwarfed by the huge glass! Pictures please!