• This topic has 1 reply, 2 voices, and was last updated 4 years ago by Michael.
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    • #6380

        Hi all !

        Let’s continue the oscillator story with the Hartley oscillator !

        The Hartley oscillator consists of an active component (such as a transistor) with a LC circuit.

        Typical for this kind of oscillator are 2 magnetically coupled coils (such as a transformer) and 1 capacitor.

        When we look in our Lectron set, we will find such a transformer, it’s the high voltage transformer.

        This transformer has 3 magnetically coupled coils.

        L1 has an inductance of 106 mHtransformer

        L2 has an inductance of 9,4 mH

        L3 has an inductance of 0,2 mH



        Since L1 has a high inductance, the frequencies produced here will be much lower and enable us to do some cool  modifications.

        But first, let’s build the circuit with a NPN transistor :

        Hartley oscillator NPN

        And here for a PNP transistor :

        Hartley oscillator PNP

        As much as possible, I will publish circuit with the (older) PNP transistors as well as with the modern NPN transistors.

        When finishing the assembly, press the switch while adjusting P1 and P2.

        By fine adjustment of P2, it’s possible to obtain a pure sine wave.

        P1 controls the pitch of the tone.

        L1 and C3 form the so called tank circuit (a parallel combination of a capacitor and inductor) and is responsible for the tone generation.

        Ready for some great experiments ? Try these out and be surprised !

        • Remove and add the ground block at C3 and listen to the sound difference.
        • Try other values for C3 (don’t use any values larger then 0,47µF)
        • Try other values for C2. Try also a 10µF capacitor (+ connected to the Base for a NPN transistor, connected to the Base for a PNP transistor).
        • Change the 1,5K resitor for a straight wire block.
        • Remember to use P1 and P2 !
        • Add a choke coil block between TR1 and P2.
        • Change R1 for other values and hear the sound chaning !
        • You found more experiments ? Share them with us !

        All possible sounds are created here : from sirens to birds twitter, from clock ticking to rainfall.

        Compare the sounds produced by the 2 circuits (NPN and PNP version).  You can clearly hear  the differences due to the build in resistor of 100K with the PNP transistor block, which influences the biasing of the transistor.

        Remember to use your oscilloscope to measure the waveforms !

        Happy experimenting !

        • This topic was modified 4 years ago by Michael.
        • This topic was modified 4 years ago by Michael. Reason: Changed font and size styling for easier reading
      • #6383

          Hello Professor Frank,

          Your detail of circuit exploration continues to amaze me!  Thank you so much.  I wish that Georg Greger could see what you do to continuously expand the Lectron Universe.


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