This circuit for very low frequencies was found in an American documentation from the 90's. Transistors are for general use and the frequency depends on C1 and C2.
This circuit was found in a publication in 2002 and can be powered by voltages from 5 to 12 V. The...
Found in an American 80's documentation, this circuit can use common FETs like the BF245 and cover...
Found in a publication for radio amateurs from the 1980s, this circuit amplifies signals in the 60...