Colpitts Audio Oscillator


When I needed a simple audio oscillator for, for instance, continuity testing or Morse practice, I wanted to make it as simple as reasonably possible. 

I thought I would try to use a standard telephone earpiece's inductance as the L of a Colpitts oscillator, and in so doing eliminate the need for a separate amplifer/buffer. 

This is the circuit.   I think the transistor is a ZTX237, but any common one should work.





And here is a picture of one.