This circuit for very low frequencies was found in an American documentation from the 90's. Transistors are for general use and the frequency depends on C1 and C2.
Found in a 90s Popular Electronics, this circuit is interspersed between the filter and the...
This circuit is from an 80's documentation. The integrated circuit is from the time and the...
This circuit was found in a 80s American documentation. The zener diodes determine the points of...