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 BC546 is a high frequency NPN Transistor commonly used in low noise amplifier designs. It has a maximum gain value of 800 and a high collector to emitter voltage of 65V making it also suitable for high voltage audio amplifier applications.
The MPSA18 is a General Purpose NPN Transistor which can operate with low noise and high gain. The transistor has a gain value of 500 to 1500 and can operate at a voltage of 45V with 200mA load current.
The KST42 is a SMD package NPN Transistor that has high collector emitter voltage of 300V and a collector current of 500mA. The transistor is a general purpose transistor and can be used for both switching and amplification purpose.