The BF423, BF-423, 423 is a High Voltage PNP Bipolar Transistor is designed for general purpose amplifier applications. This device is housed in the TO-92 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.
The 2SK2850, 2SK-2850, K2850, 2850 Is a 6A 900V 125W N-Channel MOSFET Or Field Effect Transistor TO-3P Package 3 Pin Leads, Product Manufactured by Company Fuji Electric Corp.