This crystal or galena radio uses a germanium diode. C1 is an old radio variable and L1 has 100 turns of 26 or 28 wire in a 1 inch PVC pipe. The antenna must be a long wire.
This simple charger was found in a 1980s documentation. The transistor may be the TIP42 with a...
This circuit is used to run light bulbs around street signs. Incandescent lamps up to 40 W are...
This high frequency or RF amplifier was found in a 90s Popular Electronics. The circuit can be...