DIY Point-Contact Iron Pyrite Diodes

These are my first and second point contact diodes that I have made, compared on the bottom with a commercial Sylvania 1N34 germanium diode.

They are each constructed with a fuse, a resistor, a piece of pyrite, and a thin wire for the whisker.

With a heat gun, it is very easy to remove the endcaps from a fuse. It is then cleaned, and in the case of Mk. 2 the caps are filed down and the glass tubing is cut shorter. If there are no existing holes in the ends of the end caps, a small hole is drilled in each.

Next, a film resistor is hammered gently to remove its outer coating. One of the pressed-on leads with endcaps on the ceramic rod is removed and cleaned, while the other remaining lead is cut off flush with the resistor. These will be the two leads of the device, the wire with the cup at the end will hold the pyrite crystal while the other plain lead will be attached to the whisker.

The small cup at the end of the cupped lead is filled with solder, and a tiny fragment of pyrite (accessible everywhere) is pressed into it with tweezers until the solder solidifies around it. The other remaining lead is soldered to a very fine coiled strand of wire to act as the whisker. Both of these leads are soldered into the holes in the end caps of the fuse.

Before fixing both leads to the glass tube, the crystal must first be cleaned of any grease or oil with solvent. I just use acetone. For the lead on the crystal size (cathode), I very gently use hot glue to mount the glass tube over it. On the whisker end, I just barely crimp the end cap in three places with a drill chuck, and then press it on to the end of the glass tube. This allows for the inevitable adjustments.

Once you get it going (poke around with the whisker until it works), it performs satisfactorily for use in crystal radios. Of course not as well as the 1N34, but it is very usable. Hitting it hard on a surface can sometimes dislodge the whisker, so I guess just don’t do that lol. For some reason or another (oxidation being a possible reason), they don’t work forever. You will always eventually have to open it and readjust the whisker even if you aren’t banging it around.