upon semi conductor switching and timing circuits to control the discharge from a pair of capacitors rather than upon an output transformer application_number US 68689600 A description the description of the invention is best understood with reference to the figures in which some proportions have been exaggerated or shown in schematic form for the purposes of conceptual illustration the blasting machine of the preferred embodiment is useful for example in the oil industry for oil well casing perforation as such with reference to fig1 a well bore such as may be made for an oil gas or other well is shown as 20 it has an inner steel casing 22 with a more or less annular concrete filling 24 between casing 22 and bore 20 a formation or stratum of oil bearing rock is indicated as 26 a perforating gun assembly 28 has been conveyed down bore 20 on the end of a wireline 30 by which it is physically located in the well the distance down the well may be 1000 m or more up to 7 500 m beneath the ground surface wireline 30 also electrically connects assembly 28 with a high frequency blasting machine 32 located on the surface perforating gun assembly 28 has at its upper end a collar locator 34 to which wireline 30 is attached depending therefrom perforating gun assembly 28 includes a tube 36 containing a series of shaped charges 38 connected to a detonating cord 40 cord 40 terminates at a detonator 42 by which cord 40 and then charges 38 are ignited in use an electrical signal originating at blasting machine.