This high impedance headphone amplifier was found in American documentation from the 1990s. Any general-purpose FET can be used.
This power supply is protected from shorts in the load. The BD135 must be mounted on a heatsink...
Found in a 1966 publication, this circuit is a simple version of a field strength meter. The diode...
The basic idea of this 1989 circuit is to trigger a relay for a while when a call signal occurs on...