Uploaded April 2013 | Updated September 2026, 3 weeks ago

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How to make a razor blade diode for a crystal radio/foxhole radio. This involves using a pencil and a slightly modified razor blade to make a diode to use in place of a germanium diode. To modify the razor blade, heat it with a propane torch or the flame from a gas stove until part of it has a bluish color. This is a coating of iron oxide which acts as a semiconductor for the diode. Connect the uncoated end to the earpiece and the coated end to the coil, and capacitor if you have one.

To see how to make the crystal radio in this video, watch "How to Make/Build a Crystal Radio":
youtu.be/VqdcU9ULAlA

To see how to make the earpiece amplifier shown in the video, watch "How to Make Amplifier for Crystal Radio Earpiece":
youtu.be/cQ-LxMDrD_o

To see details of how a crystal radio works, watch "How a Crystal Radio Works":
youtu.be/0-PParSmwtE

To see how to make your own crystal earpiece like the one in this video, watch "Make Crystal Earphone/Earpiece for Crystal Radio - Homemade":
youtu.be/OVapqz4yBCY

For a better amplifier, one that plays on a loud speaker, see "How to Make Crystal Radio Amplifier for Speaker":
youtu.be/JtPwxbOgBHw

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Music used at beginning and middle:
The Path of the Goblin King Kevin MacLeod (incompetech.com)
Licensed under Creative Commons: By Attribution 3.0
creativecommons.org/licenses/by/3.0
ISRC: USUAN1100873

Music used at the end:
Maraton Man
Music by audionautix.com