The 2SC1061 is a NPN Power Transistor in To-220 package. It has a DC current gain from 35 to 320 and transition frequency of 5MHz. It is commonly used in high power amplifier application along with its complementary PNP part 2SA671.
The BD243C is a 6A, 100V NPN Bipolar Power Transistor is designed for use in general purpose amplifier and switching applications. BD243B, BD243C (NPN); BD244B, BD244C (PNP) are complementary devices.
The BC558 is a PNP transistor hence the collector and emitter will be closed (Forward biased) when the base pin is held at ground and will be opened (Reverse biased) when a signal is provided to base pin.
The 2N5551 TO-92 NPN High Voltage Transistor 160V 0.6A. NPN high-voltage transistor in a TO-92; SOT54 plastic package. PNP complements: 2N5400 and 2N5401.
The IRFZ44N is a 55V 49A TO-220 Package MOSFET family of power MOSFETs utilizes proven silicon processes a wide portfolio of devices to support various applications as well as battery powered applications.