Found in a 90s Elektor, this circuit makes use of general-purpose transistors, except T4 that can be replaced by an equivalent.
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...