I got a new amp last week. A tweed Princeton 5f2a clone. The amp was great just as it came but never one to leave well enough alone I replaced the JJ tubes, a 6V6, a 12ax7 and 5Y3 GT rectifier with vintage tubes. An RCA 12ax7 and 5Y3 and a GE 6V6 GT, all pre 1970 manufacture and USA Made. I can't decide if all I got from it was a little mojo knowing the vintage tubes are in there. My initial listening test tells me that any tone change was subtle at best. Volume seems similar but I would need more testing, putting the JJs back in for another listen to make any real comparison. Was I expecting too much?