This circuit is from a 60's documentation. The capacitance C1 can be between 20 pF and 0.01 uF depending on the generated frequency. Equivalent transistors may be employed.
The circuit presented may use any general purpose transistor. The indicator is an LED and...
The circuit shown uses the LM324, but can be implemented with other operational ones. The source...
This circuit was obtained from an English publication from the 70's. The circuit is still current for...