Abstract: A liquid cooling system cools a plurality of RF power amplifiers utilized in a high power AM broadcast transmitter. Each RF power amplifier includes a thermally conductive block to which the power transistors associated with that amplifier are physically mounted. The heat generated by the power transistors is conductively transferred to the thermally conductive block. A liquid cooled plate comprising a thermal block and coolant pipes running through the thermal block is also provided. The liquid cooled plate is positioned so that the thermal block is in contact with the thermally conductive block of the RF power amplifier. A pump circulates liquid coolant through the coolant pipes. The liquid cooling system cools the power transistors by transferring the heat from the thermally conductive block through the thermal block of the liquid cooled plate to the liquid coolant flowing through the coolant pipes.