This circuit was found in a publication by Edelman from 1924. The power comes from the battery and the listening is through a high-impedance headphone.
Found in a Popular Electronics from the 90s, this game can be seen in other configurations on this site. The...
This control for a heating element was found in an old documentation. The current in the element...
This circuit is from an American documentation of 1975. The FET may be the BF245 and the relay is of...