Abstract: A D.C. arc welder with solid state components which is provided with means for converting A.C. to D.C. and with controlled diodes serially connected in the D.C. line between the converting bridge and a transformer providing electric insulation between the D.C. line and the terminals of a welding head. A further controlled diode is also connected to the D.C. line downstream of the control diodes and in parallel with the transformer and in series with a capacitor. Between the transformer and the welding head a rectifying assembly is arranged. The serially connected controlled diodes are simultaneously triggered by a pulse amplifier and transformer. A further pulse amplifier and a further pulse transformer subsequently trigger the further controlled diode, whereby the serially connected controlled diodes are turned off.