Abstract: An electromagnetic hammer rapper having forward and retract coils for controllably causing a centrally disposed armature to impact an impact transfer pin to cause the transfer pin to knock-off slag and other encrustations from heat transfer tubes or walls of heat exchanger components, and for causing the armature to be propelled to a retracted position. An electrical circuit for controlling energization of the forward and retract coils is also provided and includes a manually actuatable switch for initiating an impact between the armature and the transfer pin. An auto sequencer/manual selector circuit controls the forward and retract coils of a plurality of electromagnetic solenoids. A phase detection and triggering circuit having an operator adjustable phase control controls the duration for which the forward coil of each electromagnetic solenoid is energized.