BD139 NPN Audio Driver Transistor

BC139 Audio Driver
NPN Transistor Schematic Symbol

You may see these listed as BD139-10 or BD139-16.  This is similar to the gain grouping denoted by the C suffix on the BC549.  The -16 suffix indicates the higher gain grouping.  You can use either in this circuit.   Alternatives that will definitely work in this circuit are BD137, BD135.

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