This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
The basis of this circuit is the 723, an old integrated circuit not easier to find these days. The...
This circuit was found in a May 1981 Radio Electronics magazine article. The circuit is offset...
The circuit presented was found in a Japanese magazine in 1973. The circuit uses transistors of...