Abstract: An easily installed thermal coupler inserted in the extruded section of a heat sink on which a transistor amplifier is mounted and positioned on a circuit board in thermal contact with diode biasing means coupled to the transistor amplifier. By thus thermally coupling the biasing means with the amplifier in a self-correcting, negative feedback loop, stable transistor operation is achieved and thermal runaway prevented. Employing a unitized metallic heat conducting member having a base plate including connecting studs for circuit board mounting and an upright member extending therefrom, the heat coupler may be used as either a heat sink or heat transfer device in carrying heat either out of or into the circuit board.