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I'm trying to simulate a hartley oscillator in Pspice using an ua741 amp. The results are not oscillations..I don't understand what's the problem.. enter image description here

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    \$\begingroup\$ Where did you get this schematic or did you "design" this yourself? The schematic is weird as it has an inductor directly at the output to ground. That shorts any DC offset at the output. Opamps don't like that. \$\endgroup\$ – Bimpelrekkie Jun 15 '18 at 6:19
  • \$\begingroup\$ A circuit capable of oscillations (yours might be one) can fail-to-start in a simulator - it need a "kick" start. You might try adding some initial current in L1 or L2 with a PSPICE ".IC" directive. In a real oscillator, noise provides this service. \$\endgroup\$ – glen_geek Jun 15 '18 at 12:25
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This is more or less the circuit you should consider if you were designing a COLPITTS oscillator: -

enter image description here

  • Note that R3 is needed else it won't have enough phase shift to generate an oscillation
  • Note that the capacitors and the inductor used are not low impedances unsuitable for use with an op-amp
  • Using 50 uH and 100 uF are to radically low in impedance to work with an op-amp

So, simulate this COLPITTS as shown and then move on to making it run at 10 kHz (as per your Hartley intention) by lowering inductance and capacitance by the same ratio. Then play around with different ratios of L and C and see where the limitations are.

Remember also that these circuits can take a short/medium period of time to begin oscillating so don't expect a sine wave at the instant you switch on. Neither should you expect anything bordering decent sine wave purity. More than likely the waveform will clip against the rails or look triangular in nature due to slew rate limitations in the op-amp. Most good sinewave oscillators measure the output amplitude and control the gain (R1 and R2) to keep the amplitude stable and avoid clipping.

Then transfer this to a HARTLEY design by using inductors in place of C1 and C2 and a capacitor in place of L.

Also note this regarding the use of the 741.

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