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Question: "MOSFET did not get sufficient voltage at Vgs(th) to turn on..what correction"<br/>
Answer: Since there is an oscillator, make a charge pump (voltage double or triple). Then switch that voltage on the FET gate. <br/>

One thing you may try, just to see it on the simulator is:<br/>
Shift the operating point, by adding two resistors and a capacitor<br/>
1.5V--Ra--(X)--Rb--GND, (X)--FET gate, (X)--Cx--555 output.