LEGO System 4548 Speed Regulator

LEGO 4548 Transformer and Speed Regulator is a Trains 9V accessory set released in 1991, containing 3 pieces. It includes a 9V transformer, a dial-type speed regulator, and a connecting cable used to power and control LEGO 9V train motors. The regulator provides twelve positions with forward and reverse operation, offering six speed settings in each direction. Designed for the 9V track system, it supplies variable power for trains and compatible 9V accessories.