RC Circuit suggestions

For the neon bulb the turn-on voltage is about 70 V and the turn-off voltage is about 50-60 V.  Make sure there is a current-limiting resistor of at least  10 kΩ.  Don't crank the power supply much higher than 80 V.

 For the integrator a capacitance of 0.15 μF and a resistance of about 2kΩ and a frequency of 2 kHz works well.