BC109B Bipolar Transistor

• Type: NPN
• Collector-Emitter Voltage, max: 20 V
• Collector-Base Voltage, max: 30 V
• Emitter-Base Voltage, max: 5 V
• Collector Current − Continuous, max: 0.1 A
• Collector Dissipation: 0.3 W
• DC Current Gain (h_fe): 200 to 450
• Transition Frequency, min: 150 MHz
• Noise Figure, max: 1.5 dB
• Operating and Storage Junction Temperature Range: -65 to +175 °C
• Package: TO-18

Here is an image showing the pin diagram of this transistor.The BC109B transistor can have a current gain of 200 to 450. The gain of the BC109 will be in the range from 200 to 800, for the BC109C it will be in the range from 420 to 800.The complementary PNP transistor to the BC109B is the BC179B.The MMBTH10 (SOT-23) is the SMD version of the BC109B transistor. These transistors are of the same type, have similar parameters and are designed for surface mounting.You can replace the BC109B with the BC108 or BC108B.