June 2016
I inherited an antique “cat’s whisker” crystal radio set. Everything seems to be intact except the actual crystal that the cat’s whisker touches. Any ideas on where I can find a replacement crystal?
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As a boy, I used a piece of “galena” from my rock hound father's rock collection. Ask around for companies that cater to this hobby. I also experimented with making my own crystals. Get an old fashioned 100% copper penny or go to a hobby store and get a strip of copper. You need to get the penny (copper) perfectly clean. Put 1 tsp (5 g) of salt into 1/4 c (2 oz) of vinegar (or lemon juice). Soak the penny for 5 to 30 minuets. Wash the penny well with plain water.
Heat the penny from the backside using a small torch, or the flame of a gas stove, or laying it on the red-hot burner of an electric stove. When the penny develops a reddish sheen (cuprous oxide), remove it from the flame and it is ready to use. Clean a small spot on the edge of the penny with a piece of sandpaper and connect it to your crystal radio. Then use the crystal radio’s cat whisker to probe the reddish area to look for a hot spot.
You can also cheat (not an option when I was a young boy) and use a small signal diode like a 1N34 or similar.
The REAL secret to a crystal radio is to use a set of high impedance earphones. Today’s earphones are mostly all low impedance and will not work unless you use an audio impedance matching transformer between the crystal radio and the earphones.
The crystal most often used for old-time cat's whisker crystal radios is a naturally occurring mineral, galena, which is an ore of lead (lead sulfide). Galena is a naturally occurring semiconductor. The point contact of the whisker (a piece of wire) and the mineral form a rectifying junction. You can find samples of galena at many tourist gift shops, some museum gift shops, as well as from some online sources. It is a shiny black mineral and a small piece should not be very expensive.
According to my father, who used to play with cat's whisker radios when he was young, making a good rectifying contact takes considerable patience and the contact will age and so will need to be redone every now and then. More reliably, but with less historical accuracy, you can replace the whisker/galena portion of the radio with a small-signal semiconductor diode, which is what I did when I was young. A germanium diode, such as a 1N34, is usually better for this than a silicon diode, due to the lower turn-on voltage of germanium.
First off, the crystal in a crystal radio was made from "galena," but if I remember correctly, you could also make this work with two pieces of dissimilar metal or a modern diode. The way these were made originally was with a pin and a rusty shaver blade; the pin touching the blade made a crude diode, which rectified the signal on the RF carrier. The rust was very important, it was what helped make the crude diode. Pencil lead was better to use instead of a pin because further rusting would ruin the diode effect and lead won't cause further rusting/oxidizing. The thing wanted is two dissimilar metals so that there is a charge gradient, the thing that causes dissimilar metals when touching to oxidize. Most touching dissimilar metals, if picked correctly, will act as a sacrificial anode. In other words, it acts as a diode. A diode that could be used is the 1N34. see: www.techlib.com/electronics/crystal.html
Here's another really good article: https://en.wikipedia.org/wiki/Crystal_radio and I quote, "It gets its name from its most important component, known as a crystal detector, originally made from a piece of crystalline mineral such as galena.[1] This component is now called a diode." and "The lead point touching the semiconducting oxide coating (rust) on the blade formed a crude point-contact diode." and " The lead of the pencil is made of graphite and clay and so it would inhibit further corrosion that would result if copper or iron wire was used in its place."
You can find replacement cat-whisker/crystal assemblies on eBay, but they're quite expensive. A simpler solution is to replace the cat-whisker/crystal assembly with a germanium signal diode — 1N270 or 1N34. Identify the non-banded (anode) end of the device case and connect it to the cat-whisker holder. The banded (cathode) end connects to the crystal cup holder.
You need what is known as a Galena crystal. You can find these on eBay, etsy, and similar websites. I found several listings under $10. If you need the entire detector including the stand and adjustable wire, google "cat's whisker detector".
These detectors were in use at the very beginning of the last century, before vacuum tube detectors were available. They create a semiconductor diode, using a fine wire (the "whisker") just touching the Galena Crystal. Getting them to work was and is something of a black art because not all areas of the crystal will act as a diode when touched by the wire, and they are sensitive to pressure, movement, and vibration. If you want to play with the radio receiver without having to adjust the crystal every time, you can replace it with a 1N34A germanium detector diode. These are available on eBay and also at any electronic component distributor for a couple of dollars.
You need a small piece of the mineral galena (lead sulfide), although some crystal radios use pyrite (iron sulfide), also known as Fool's Gold because of its color. Borden Radio Company sells galena crystals for $5.00. www.xtalman.com/detectors
Use a 1n34 diode.
The most common mineral used for cat’s whisker detectors is Galena (Lead(II) Sulfide). This is readily available from mineral/fossil collection suppliers and many hobby stores. It’s cheap and you only need a tiny piece. Some museum shops and toy stores also sell it but you may have to buy a collection. It can also be found on on-line auction sites. G8RPI.
I searched the internet for "crystal radio" and got millions of hits, including Amazon.com. Just search.
You can replace the cat’s whisker and lead galena crystal with a 1N34 diode; but if you want the real thing there are two choices:
The crystal is galena or lead sulfide. The crystals may be found on ebay or other gem sites. My crystal was embedded in lead with at least half showing. It's tricky to get a good spot. Happy gem hunting!
The crystals used were small chunks of galena (or pyrite, i.e., “Fool’s Gold,” I believe?). Because the “atomic structures” of the crystals used were, at best, iffy, it took a lot of practice to find the right spot(s) on the crystal that would give a strong, usable signal. You can get some galena and/or pyrite at any rock shop. Just make sure you don’t get any polished crystals — you want the surface to be as raw as possible, but make sure it’s clean.
Building crystal radio sets (of wide variety) was one of my hobbies for years. I would suggest keeping it authentic by making your own replacement. This is not difficult. Here is a great source of information: http://bizarrelabs.com/crystal.htm There is much more information to be found. Crystal radios still have quite a following!
