BC109 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 800
• 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 BC109 transistor can have a current gain of 200 to 800. The gain of the BC109B will be in the range from 200 to 450, for the BC109C it will be in the range from 420 to 800.The complementary PNP transistor to the BC109 is the BC179.The MMBTH10 (SOT-23) is the SMD version of the BC109 transistor. These transistors are of the same type, have similar parameters and are designed for surface mounting.You can replace the BC109 with the BC108.