2N3773 This is an NPN Bipolar Power Transistor
It is used for high power audio
This transistor can work up to 16 amps and 140 volts
This transistor has 3 pinout
The body of this transistor is the collector
Apart from this the transistor also has base and emittor
Because it is an NPN transistor i.e. Negative Positive Negative, hence the plus positive supply is given to its collector.