BC639G NPN Epitaxial Silicon Transistor Switching and Amplifier Applications, ECB, TO-92 Package. Used on Hantarex monitors such as MTC9000, MTC9010 at TR14, TR18, TR22 and any other application that requires this transistor. The BC639 is higher rated and can replace the BC635, 2SC3203 and BC637. These are used on many monitor and other applications. For every quantity of 1 added to your cart you will receive 5 transistors.