This crystal or galena radio was found in documentation from the 1990s. The earpiece must be a high impedance crystal or magnetic earpiece and D1 can be any germanium diode.
In the figure we show how to implement a voltage reference with the ON Semiconductor rail-to-rail...
This circuit is from a technical documentation from 1978. The maximum output current is of the...
This RF and audio follower applies its signals to a small amplifier. The FET can be any...