This simple neon lamp oscillator produces a 140 Hz, 40 V peak-to-peak signal. The frequency is given by the capacitor that can have its value changed. Note the high supply voltage.
The sensor for this Intersil circuit (1983 databook) is a common silicon transistor. The trimpot...
This circuit is from a 1980 publication. The circuit has high gain with weak signals and lower gain...
The integrated circuit used in this 1987 project is not very common these days. However, if found...