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 k $\Omega$ $\Omega$ . Don't crank the power supply much higher than 80 V.

For the integrator a capacitance of 0.15 $\mu$ $\mu$ F and a resistance of about 2k $\Omega$ $\Omega$ and a frequency of 2 kHz works well.