I've wasted a lot of time and money building single variable capacitor crystal radios. They just don't work. If this one does not work, it's the last one I'm going to build. I'm done with them!

I found this design on the internet. It's from the 1950s, rather late in the game (many were from the 1920s).

MATERIALS
1 x 1n34a diode
Board (Mine is 18cm x 12cm)
1.25" (1.65" actual) PVC pipe (42mm) x 140 mm long
20 gauge wire (0.81mm)
16 brass or stainless screws
10 brass washers
2 pillow blocks (wood or plastic)
1 10365 pF air tune capacitor
1 bracket for capacitor
2 Fahnestock clips
1 resistor 10k40k ohms
1 crystal earphone (piezoelectric)

3D Printable Pillow Blocks: https://www.thingiverse.com/thing:643...
3D Printable 360 pF Variable Capacitor Mounts (2 types): https://www.thingiverse.com/thing:643...

TOOLS
Screw driver
Knife
Sandpaper (small piece, fine)
Saw, if you do not have the wood & tube already cut
Hand drill for screw holes
(Optional) Soldering iron, solder

ANTENNA & GROUND
Antenna are just a long piece of wire (I use scrap wire from old transformers). The longer the better.
Try different lengths and orientations (vertical, horizontal)
A good ground helps. A wire to a ground rod is good. Metal water pipes also work well.

NOTES:
The resistor is necessary to get the best sound from these "new" crystal earphones. The new ones are piezoelectric and have lots of capacitance. Without the resistor the charge builds up then discharges so you get constant "static" sounds. The resistor bleeds off charge so you get louder, and much clearer sound.

WARNINGS:
Never connect radio to any source of power. Not house current, nor batteries, nothing!
Never use the radio during lightning storms.
Never run an antenna over or near power lines.
Disconnect antenna and put lead outside when not in use.
Never ground to electrical items, plugs or similar.
If you don't know, don't do it.

OSCILLOSCOPE USED:
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INTERESTING LINKS
Knob For Variable Capacitor & Similar (D & Round Shaft Versions) https://www.thingiverse.com/thing:633...
Knobs for capacitor tuned crystal radio. https://www.thingiverse.com/thing:619...
Air Core: http://www.circuits.dk/singlelayera...

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