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 an English documentation from 1989, this font uses current components. Rectifier bridges can...
This sensor circuit for currents of the order of nanoamperes was found in an American...
This TTL sequential flasher circuit was found in the January 1981 issue of Radio Electronics...