Vintage 21TE31 thyratron is a gas filled tube with tetrode construction which was designed for relay or grid-controlled rectifier applications. 21TE31 is directly replacing the thyratrons PL21, 2D21, CV797, RL21, ASG5121, TXM100, 20A3 and some others. All of the available pieces are tested and working. New old stock. Years of production: 1958 (SF code) and 1966 (DY code).