The C945 is an age old Japanese Bipolar audio frequency NPN transistor 60V 150mA TO-92 package. It has a decent gain value (hfe) of maximum 700 and is highly linear. Hence it was widely used in amplifier.
The MJ802G MJ802 802 is a 100V 30A 200W transistor, Use for as an output device in complementary audio amplifiers to 100−Watts music power per channel.
The 2SK2837, 2SK-2837, K2837, 2837 is a 500V 20A N Channel Silicon Field Effect Transistor Or MOFET TO-3PN-3 Package. Chopper Regulator, DC−DC Converter and Motor Drive.