GB763545A - Improvements in or relating to travelling wave tubes and the manufacture thereof - Google Patents

Abstract

763,545. Travelling-wave tubes. WESTERN ELECTRIC CO., Inc. Oct. 20, 1954 [Oct. 21, 1953; Oct. 21, 1953], No. 30211/54. Class 39(1). In a travelling-wave tube comprising an electron gun assembly 10 and a collector assembly 11 connected by an elongated glass envelope 12 enclosing a helix 14 supported by three rods 15 preferably of ceramic material, increase in the temperature of the helix, due to excess radio frequency power which the helix is unable to transmit with consequent decrease in power output and efficiency, is reduced by collapsing a portion 18 of the envelope 12 into intimate contact with the rods 15 over a significant portion of their periphery. The length of the portion 18 is preferably about one third the length of the helix 14, and the envelope is collapsed from the shape shown in Fig. 2 to the shape shown in Fig. 3 in which the envelope is in contact with the rods 15 over a third or more of the periphery of each rod. The collapsing operation is carried out using the circuit arrangement shown in Fig. 6. An aligning tube 24 at one end of the helix 14 is connected by a lead 31 to a terminal pin 17, and a support ring 28 at the other end of the helix is connected through a fuse wire 30 to the collecting cylinder 27 to establish through the helix a direct current path which is completed by a lead 32, switch 33 and battery 39. The envelope is exhausted by a vacuum pump 36 connected by rubber tubing 37 to the collector cylinder 27, and current is passed through the helix sufficient to soften the glass envelope but not to such an extent that collapse occurs. A heat reflecting cylinder 40 is placed around the envelope to provide the additional heat necessary to allow atmospheric pressure to collapse the envelope. The cylinder 40 may cover the whole length of the envelope to be collapsed, or may be moved along the envelope, and is provided with a thermocouple 42, preferably in contact with the envelope 12, and a meter 43 to enable the collapse to be stopped before the envelope comes into contact with the helix. Either before or after the collapsing operation, the cylinder 40 is removed and the helix outgassed by passing a current through the direct current path. When evacuation has been completed, the fuse wire 30 is burnt out by application of a short high current, and the collector cylinder 27 is then sealed off. Specifications 726,823 and 734,771 are referred to.