This circuit was found in a 1926 German publication. It is a crystal or galena (D) receiver. The crystal (D) can be replaced with a germanium diode. The phone must be magnetic, or if it is made of crystal it must have a 22k resistor in parallel. L1 is formed by 10 turns over L2, and L2 by 65 turns of 0.5 mm wire (can be 28) in a cardboard tube 8 cm long and 1 inch in diameter. C2 was specified at the time in centimeters (!), But a 1nF ceramic capacitor will do. Likewise, C1 can be an old transistor radio variable. The antenna must be long. In the figure the page in German of the original publication.
