This circuit was obtained from Popular Electronics of the 1990s. The circuit uses common transistors today and the frequency is given by the crystal.
We found this circuit in a 90's Radio Electronics. The low power circuit activates a 12 V relay...
This general-purpose two-transistor circuit was found in the November 1993 issue of Electronics Now. The...
We found this circuit in an American 1980s documentation. The operational ones used are not common...