There should also be sockets for a 6AN8 tube(phase inverter) and 12ax7(the actual preamp tube...the 12au7 tube is the reverb driver). If there is a metal cap on the chassis where it looks like a tube shocket might be, or no cap at all, you have a solid state rectifier; if there's one more larger tube socket unaccounted for, you'll need a GZ34 tube rectifier. This amp configuration(2x6550/KT88 power tubes =60watts) went by several different names, 100s, Solarus, Sceptre; earlier versions may not have rev/trem circuits, but you can check the "schematics" link at the bottom of the main page here for more info, or else check Aspen Pitmann's "Tube Amp Book".