A semi-controlled RST 2x 1250/ 1250 rectifier for traction is used to charge with variable direct current voltage a group of traction motors with series excitation. The motor group is made up of two LJE – 108 motors, connected in series. The semi-controlled RST 2x 1250/ 1250 rectifier for traction transforms the alternative voltage in the traction secondaries of the main locomotive transformer into adjustable direct voltage, by the connection in series between a double semi-controlled bridge in economic assembly (RST 2 x 625/ 1250 PDME) and a simple semi-controlled bridge (RST 1250/ 1250 PS). This is the functional equivalent of four rectifier bridges that are connected in series.