This circuit is from a 1976 amateur radio manual. The transistor can be the BD136 and the frequency adjustment is done in a potentiometer. The supply can be done with voltages from 6 to 15 V.
This circuit was obtained from a Radio Electronics from October 1963. The 4 transistors must be...
This shield circuit is from an American documentation from 1969. The components can be modified...
This circuit for very low frequencies was found in an American documentation from the 90's....