Found in a QST magazine from the 90s, this circuit broadcasts on different amateur radio bands depending on the coil. Data for the coil and crystal are provided next to the diagram.
Suggested by a 1966 publication, this circuit applies a 60 Hz signal to a transistor to test its...
This circuit is indicated to operation with piezoeletric transdicers or other with high impedance...
Two operational amplifiers are used in this source obtained in an American documentation...