MANUFACTURE OF MAGNETRON

PURPOSE:To obtain a highly reliable magnetron by using a tapering multistage tool as a pinch-off tool. CONSTITUTION:A tapering multistage tool is used as a pinch-off tool 18. For instance, said tool is formed by combination of not less than two radiuses of curvature having different central positions while being composed of two radiuses of curvature R1 and one radius of curvature R2, whereby R1 is 3mm. and R2 is 2mm., while the central positions of two R1 are located in the different spots as shown by O and O'. Further, R2 is provided to smoothly connect two R1, to each other whereby its central position is located in the position different from the central positions O and O' of two R1. In the state chipped-off by the pinch-off tool 18, the opening of the pinching part 17 gets very small, the length of the welding part of an antenna conductor 9 and an exhaust tube 15 gets long thus lengthening its life.