This 1924 receiver uses a battery for the tube filaments and a high voltage battery for the amplifier and detector circuit. The speaker is kind of high impedance era.
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...