The tube at left, rebranded as United type "45", is actually a type 2A3. The tube at the center is a genuine type 45 and the tube at the right is a correctly marked 2A3. United was an old US maker of transmitting and industrial types. They NEVER made receiving tubes. Someone else owns the brand name and has used it to rebrand many types. The 2A3 is a poor sub for a type 45, chiefly because the filament of the 2A3 draws a full 1 amp more per tube. Since most radios and amplifiers use type 45 tubes in pairs or quartets, this would significantly tax the power transformer. The good news is that now 2A3 tubes are pretty valuable themselves, so the fake is not a total loss.