We found this circuit in the Radio Electronics magazine of May 1977. The circuit has the frequency given by the components according to the formula next to the diagram.
This circuit was obtained from an American 80's documentation. The operational ones can be...
This audio amplifier from the 70's uses a high voltage transistor. The transistors are from the...
This circuit can be found elsewhere on this site as part of alarms or sirens. The circuit given is...