Owing to the demands of industry for a permissible 50-cap blasting machine, the Bureau of Mines contracted with Magnavox Company to design such equipment. From the preliminary analysis of the technical requirements of the blasting machine, a new electrical design, which would eliminate the need for mechanical switches to switch high voltage, was conceived. This new design utilized simple, straightforward techniques to overcome several problems identified in the original design and, at the same time, increase inherent reliability of the equipment. The central feature of the new circuit was a transistorized timing generator capable of driving the output silicon controlled rectifiers (scr's) directly. Approval and testing of this equipment by the Bureau of Mines has not been completed.