Understanding oscillator circuit in dc

Discussion in 'General Electronics Chat' started by DenManiac, Oct 3, 2008.

  1. DenManiac

    Thread Starter New Member

    Oct 3, 2008
    Hello all. I'm hoping someone can give a good understanding to the attached scematic. First of all, it creates a pulsing noise from the speaker and the sound gets faster as you play with the potentiometer. I would like better details such as how the current actually flows. I believe the speaker runs by inductance and changing the current direction in the transformer back an forth some how. Sorry if this is very basic for some of you. Thansk.
  2. Wendy


    Mar 24, 2008
    This is a modified Hartley Oscillator.


    It also resembles an Armstrong Oscillator, the difference isn't that clear cut to me.


    The transformer inverts the signal, and feeds it back into the common emitter BJT amp, which is an inverting amp. Since the amp and the coil both invert the signal, this translates the signal to non inverting, which means you have positive feedback. Their must be elements of a RC oscillator to vary the frequency with the variable resistor, haven't totally figured that out, but if you were to look at the waveform on an oscilloscope I suspect you'd see a large sine wave component.


    Circuits like these are what kept me in trouble with my Dad when I was a teen. Seemed like all of them interfered with our TV reception, which wasn't that great to begin with.

    BTW, nice schematic. A lot of people have to asked.
    Last edited: Oct 4, 2008