The 2SC2371 is a Silicon NPN power transistors, TO-126 package, High voltage 300V 100mA high frequency. For TV chroma output and vertical output applications.
The 2SK3515, 2SK-3515, K3515, 3515 is a 450V, 10A, 48W TO-220NIS Package MOSFET, The FUJI Electric manufacturer is a IC Chips with N CHANNEL SILICON POWER MOSFET for more details of 2SK3515 can be seen below.
The TIP140, TIP141 and TIP142 are 100V 10A 125W Silicon Epitaxial-Base NPN power transistors in monolithic Darlington configuration, mounted in TO-218 Package.
The BC547 is a NPN transistor hence the collector and emitter will be left open (Reverse biased) when the base pin is held at ground and will be closed (Forward biased) when a signal is provided to base pin.