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.
This timer with 1 second accuracy was obtained in a 1973 documentation. The Buzzer is a low-power type...
We find this circuit in a Popular Electronics of the 90s. The circuit is passive and the coils...
The basic idea of this circuit is to indicate the tolerance of a capacitor by reference to a...