MK484 Radio Circuit Stage 3

In the final stage of the MK484 radio circuit, I am using a Darlington transistor to drive a step-up transformer, which in turn drives an 8-Ω loudspeaker. Many different types of Darlington transistors will work, however I chose the most readily available and lowest-cost one, which was the MPSA13.

The BC517 is also cheap and readily available. It is an NPN Darlington transistor with a DC current gain (hFE) of 30000.

For the volume control, I am using a 10-kΩ potentiometer, which is of course a logarithmic type. This is the absolute minimum value that will work, however if you have anything bigger, then that should work as well.

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