My #17 Crystal Set — Catwhisker & Diode Detection
Is your cat missing a whisker or two?
Hello again boys and girls. Before we get started, I would invite you that are new to my crystal set site to go to the beginning and quickly read through what I have done. You can use the "next" buttons at the bottom to progress through the sets. This is my main crystal set page, with links and an introduction. I am going to try doing a little less repeating. I have built a lot of sets in the last 9 months. Have to keep it lively!
Today I am proudly introducing my #17 set, and my first one with a galena detector. You might have figured that grandpa was so grumpy because of his ill fitting underwear or teeth, or that special soap that grandma used to make him use. Not true. He got that way because he had to mess with a galena detector, rather than having a 1N34A diode hooked up. I don't want to discourage you, but having a lot of patience and a steady hand are very useful when you listen with a piece of the rock. But this can also be very rewarding. I sure had a big smile the other day when I heard my first station using a catswhisker detector.
This set is much like my #12 set. The box is the same, capacitors, coil (although I added a few turns so it would tune slightly lower in the band). The difference with this set is the dual detection. You can tune in a loud station using the diode and then change the brass link over to the galena and play play play.
Before the days of the 1N34A diodes, galena with a catswhisker was the only way to receive radio. But how did you know when your catswhisker has touched the "hot spot"? In this case, switching to the diode first helps, but in the old days they used a buzzer. The buzzer usually ran on a single D cell and was connected to the crystal set's antenna circuit. The buzzer would spit out a wide band of rf noise so it didn't matter where the radio was tuned, when you hit the hot spot, you would hear the noise. Cool, huh? I am planning on a little "side project" of a solid state rf noise generator. I might use a couple of transistors or perhaps an IC. This will be in a separate box with a switch and two terminals. It will be the same as the buzzer except you won't have to listen to the audio noise. Speaking of side projects, here is one I built a couple of weeks ago that I want you to see.
Getting back to this set, there is a brass link switch on the face of the radio to switch from a diode to the galena detector. I think these link switches look neat and work well for circuits that don't need continuous switching. The holes were drilled 3/4 inches apart. 3/4 inches are also the spacing of my other terminals as this is kind of an industry standard. The brass thumb nuts used in this set are not real expensive and they make a very nice connector. I use 8-32 hardware for most of this set.
The galena detector consists of several parts. It took me weeks to find all the stuff for this. The galena itself is set in a brass cup holder and potted with solder. This cup sits inside of a larger one that is attached to the Garolite® panel. The catswhisker mount is made from a piece of brass about 2-1/4 inches long. This brass strip is .040 inches thick and 3/8 inches wide. I don't know where to buy this in this width, so you may have to cut some. I used a small bender brake (as you can see I am still learning how to use this). The sides are about 1 inch tall. I drilled the holes after bending. The side ball mount holes are 3/16 inch in diameter. A 9/64 hole is drilled in the bottom for attachment to the Garolite®. I bought the little wooden ball at Michael's. These craft places have a lot of that stuff. The brass ball is sold by Lowe's in the lamp department. As it comes, the hole is drilled halfway through the ball and tapped with an 8-32 thread. I drilled a 1/16 inch pilot hole through the ball starting at the threaded end. Then a 11/64 drill is used to enlarge this hole. I have only done a couple of these, but seems to work out on my kitchen drill press. The next piece is a threaded rod, about 2 inches long that goes through the ball and on the galena end is a thin wire called a catswhisker. This is a springy wire that will gently touch the galena hot spot. That is how I built my galena detector stand.
This radio works very well. I was hearing a station even before the ground wire was attached! This set is made to work well with fairly short antennas, say 25 to 50 feet. A design change for this set would be to tap the main coil in a few places and use a switch to select how high on the coil the antenna capacitor will go. Just an idea for a future set.
BTW, how do you like the tan Garolite®. I thought it would be a good change but my color of choice for these sets is black. I welcome comments from the WWW community. Best wishes from -- Dave N2DS