4512V covers the LEGO trains of the 4.5 V and 12 V systems from the 1970s and 1980s. The 4.5 V trains ran on batteries carried in a wagon or tender, while the 12 V trains drew power from conductor rails laid between the running rails, fed by a transformer with a speed control. Until 1980 the track was blue, which gave these years the name of the Blue Era.
1977 LEGO Sets
1977 introduced the Expert Builder series—precursor to Technic—using beams, axles, and gears for mechanically rich models. Town-style sets broadened everyday subjects with houses, shops, and vehicles. Dedicated Space and Castle themes were still a year away, but elements and styling hinted at their imminent arrival.