A 400-ampere sealed ignitron

As rectifier capacity is increased, it becomes desirable to use larger capacity rectifying elements. The choice of rectifying element size requires careful consideration in order to provide a complete range with a minimum number of units. The sizes of industrial ignitron tubes for welding control and for rectifier service have been chosen on a preferred number scale providing a proportionate increase at each increment. The development of a 400-ampere ignitron for rectifier service was undertaken to provide the next larger size tube in the series. Development work on the 400-ampere ignitron disclosed that design problems become more complex as the physical size of the tube is increased. The ability of a tube to rectify a given current with a minimum number of arc-backs is affected by circuit duty and by control of ionization, particularly at the end of the current com-mutating period. None of the factors involved have indicated an upper limit in size, but rather a need for a more exact understanding of the phenomena involved.