Abstract: A clamp intended for the end-to-end welding of two tubes disposed in accordance with an axis (3) by an electrode (14) operating in a circular movement (18) includes two collars (1, 2), mounted pivotably around the axis (3), put into rotation by gears (7, 8, 10, 11). On one collar (1) a swinging element (13) is pivotably mounted and used to support the welding electrode (14). A cam (16) is provided on the other collar (2), which cooperates with an integral element (15) of the swinging element (13). The two collars are put in motion by two distinct motors which are connected with regulation and control devices which permit a change of the rotation speed of at least one of the collars in such a way that the distance between the electrode (14) and the axis (3) is changed. In this way the height of the arc is controlled.