This high impedance headphone amplifier was found in American documentation from the 1990s. Any general-purpose FET can be used.
This circuit can source up to 1,000 V from a 9 V battery. Output current is very low, some...
This circuit detects the presence of strong signals from spy transmitters, enabling their...
This circuit of a publication from the 70's uses a different type of power that we had already...