Hi I have a 2011 ST-120 .I have been using a quad of KT 120's from Jim McShane . I have a Webber copper cap rectifier. I want to run a tube rectifier .But I don't have the funds for an $800 GZ 37. I read about the 5U4 types and would love advise . And I need some pre tubes Tested. I have the low gain board . 12AU7,12BH7 and some 6SN7's. So testing. And I would like to buy A quad of KT88's and a sturdy 5U4GB ? or two . thanks for the wisdom .