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  • Author Author: jc2048
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The Gold of the Fool and the Whiskers of the Cat

jc2048

Back in February, I visited one of the small museums that exist in the town where I

live. It's a natural history museum and is based in an old church. It's a lovely

place to visit, with lots of curious things to look at. In the shop, on the way out,

there was a basket with small chunks of rocks and minerals for sale and I bought a

small piece of 'fool's gold' (iron pyrites); I figured that an old fool like me

deserved a piece of gold to treasure.

 

image

 

What I didn't know back then and have only just discovered is that iron pyrites is

a semiconductor (thank you, Wikipedia!) and in the old days was sometimes used as

the 'crystal' in a point-contact diode (for demodulating radio signals in a crystal

set).

 

Well, I thought, that deserves an experiment. So here is my attempt to make a

point-contact diode, and it turned out to be surprisingly easy. I simply broke one

of the small cubes away and held it in one clip of a 'helping hand' contraption.

 

image

 

That clip I connected to the ground of a signal generator. The drive from the

generator I fed through a 10k resistor to a piece of wire-wrap wire which I arranged

to scrape across the surface of the cube. My scope then measured the output from my

improvised diode.

 

image

 

A little movement of the wire and I soon found a spot that rectified nicely [I was just

so surprised - I really didn't think that this was going to work].

 

image

 

The forward voltage looks to be a little over a volt. That's much higher than a

silicon metal-junction diode (a Schottky diode).

 

And that's it. No need to melt silica in an oven and grow it into a crystal with

99.99-whatever % purity. Instead, an instant semiconductor straight from nature.

 

Do I get a cat badge for this foolishness?

Parents

  • The "radio" based on the crystal was the absolutely first stuff I have done when I was about 10 y.o. Synth was based on the semiconductor crystal (it was the early '70 so these stuff was not difficult to find. By one side the crystal was pinched in a alligator and by the other side it was possible to "synthonize" the radio station with a pin touching  different points of the crystal. The "amplifier" was just a aris insulated variable capacitor and a couple of earphones. The antenna was something like 100 meters of insulated copper in spiral (5 meters spiral). Then no power was needed, and the audio was fantastic.

     

    As I find it I have again the model and I will make some photo.

     

    Enrico

Comment

  • The "radio" based on the crystal was the absolutely first stuff I have done when I was about 10 y.o. Synth was based on the semiconductor crystal (it was the early '70 so these stuff was not difficult to find. By one side the crystal was pinched in a alligator and by the other side it was possible to "synthonize" the radio station with a pin touching  different points of the crystal. The "amplifier" was just a aris insulated variable capacitor and a couple of earphones. The antenna was something like 100 meters of insulated copper in spiral (5 meters spiral). Then no power was needed, and the audio was fantastic.

     

    As I find it I have again the model and I will make some photo.

     

    Enrico

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