I have, for some unknown reason, always been interested in ancient technology, mainly electronics and mechanical things and I have always wanted to make a true old fashioned style crystal radio. A crystal radio, or crystal set as it is sometimes called, is a radio that only uses the power of the radio waves picked up by the antenna to generate the sound heard in the head phones. The reason it is called a crystal set is because they use a mineral crystal as a diode for the detector in the circuit.

Quite a few years ago I found a book in the library called "Radios That Work for Free" by K E Edwards and found a set of plans for a radio that I just had to make, unfortunately I did not have the resources to build it at the time so I made a photo copy of the pages from the book for future reference. Well I was poking around on the net the other day and found a site that sells copies of that old book, along with various other electronics books and parts related to crystal radios and decided to order a copy for myself along with two 365 pf variable capacitors needed for the circuit I copied from the book.

The radio that I am going to build is the second one shown in the book but I am going to make some changes to the original set. The three changes I am going to make to the set are that I am going to build the set into a box instead of just having the control panel attached to a base board. I am also going to make an antique style "Cats Whisker" style detector instead of using a Germanium diode and use a matching transformer so I can use a set of modern headphones instead of trying to find an antique high impedance set or a crappy little crystal earplug.

I have written this instructable assuming the reader has basic wood working and electronics skills like making boxes and soldering, explaining the more involved and specific tasks in detail, as in winding the coil.

## Step 1: Circuit and Theory

Here is a scan of the circuit from the book. The circuit is actually pretty simple, just two variable capacitors(C1 & C2), a coil(L) with 8 taps and a tap switch(S), a detector(D) and a set of phones(P).

Without getting into the rather intensive math involved, I have taken classes on this stuff, here is in a nutshell how it all works.

Crystal radios mainly work on AM or Amplitude Modulation radio waves, there are some that well work on FM as well. AM radio waves are actually composed of two waves combined together, one is a high frequency wave called the carrier wave and the other is the lower frequency sound waves being transmitted. The carrier wave is on the order of 750 to 1500 kHz. and is used to transmit the sound wave. The way it works is that the two waves are added together, or modulated, producing a signal that is of the same frequency as the carrier wave but its amplitude is determined by the sound wave(see second picture).

The way a crystal radio actually works is pretty ingenious, it uses the coil L and variable tuning capacitor C1 as a low pass filter to only allow frequencies at the desired frequency of the carrier wave to be passed to the detector D. The detector then demodulates the signal by only letting the low frequency part of the signal to pass, ie the sound wave, to the headphones where they are then turned back into sound. There are no batteries, no transistors or amplifiers of any kind, the sound is produced solely by the energy of the filtered radio wave.

## Step 2: Materials

-Hardware:

3 x 6-32 2" long screws
11 x 6-32 3/8" long screws
2 x 6-32 3/4" long screws
6 x 6-32 1/4" long screws
4 x #6 1/2" long wood screws
22 x 6-32 hex nuts
2 x 6-32 thumb nuts
8 x #6 washers
- sheet of 1/8" thick Plexiglas for panel
1 x 1/2"x6"x4' board, I used poplar as it is cheaper and looks nice you could also use pine or oak or what ever you like.
1 x 3/8"x6"x2' board, again I used poplar
-some thin copper sheet, or brass (Scrap metal dealer or hobby shop) \$4 for a large piece
1 x 3/8" dowel (All above items are from the hardware store. I used brass but steel would be a significantly cheaper) \$9
1 x 2" diameter 5" long cardboard tube, you could also use pvc (mailing tube or hardware store)

-Electronic Bits:

1 x binding post (AES S-H226B or RS, AES has single binding posts instead of multi packs) \$2
14 x solder lugs (AES S-H112) Package of 10 from AES \$1
2 x 3/4" Fahnstock (AES)
1 x 1N34 Germanium diode
1 x 1/4 lb roll of 20 awg enameled copper wire (AES S-WL3-610 has 21 gauge wire which should be close enough)
1 x short piece of 12 gauge bare copper wire (got mine from a scrap if Romex)
2 x 365 pf air gap variable capacitors (AES C-V365) \$12 each
1 x chunk of iron pyrite (Rock shop or sometimes gift shops have things of different minerals)
1 x 1K to 8 ohm matching transformer (RS# 273-1380) \$3
1 x 1/4" stereo phone jack (RS# 274-249) \$3
2 x large knobs (RS) \$2
- 22 gauge hookup wire (RS or AES has the old fashioned style fabric covered wire which would look real good but it is expensive) \$6 for three 25 foot rolls from radio shack

-Optional:

- Stain for staining the box
- Lacquer or other clear coat to protect the box
- Black paint for the panel and tap switch knob

Suppliers:

AES: Antique Electronic Supply, has all kinds of antique style parts, vacuum tubes and stuff you generally can not get any where else. Antique Electronic Supply
RS: Radio Shack, they still have one or two things in stock that are useful.

Substitutes: The copper, iron pyrite, 10 3/8" screws, one of the 2" long screws and 12 of the nuts are used to make a tap switch and detector for the set and can be substituted with commercially made parts if you do not wish to make them by hand. The tap switch can be replaced with a 10 position rotary switch and the detector can be replaced with a 1N34 Germanium diode, both of which are available from Radio Shack. I made them on mine because I wanted to make the set as authentic looking as possible, mind you the modern substitutes would be more reliable and quicker.

-Tools:

- Hobby Knife or utility knife
- Drill and bits 1/16" and 5/32"
- Pliers, needle and regular
- Ruler
- Pencil
- Marker
- Tin Snips
- Metal File
- Wood Saw
- Hammer and 1" long finish nails
- Nail set
- Wood putty
- Wood glue
- Super Glue
- Soldering iron and solder
- Wire cutter and striper

## Step 3: Winding the Coil

To wind the coil you well need:
- 2" diameter tube
- 1/4 lb of 20 gauge enameled copper wire
- ruler
- pencil
- small drill
- pliers
- wire cutters

1) Mark and cut the tube to length:
-With a ruler mark the tube at 5 inches from on end and wrap tape around the tube at that mark.
-With a sharp knife cut along the edge of the tape to make a nice even cut.
2) Using a ruler draw a strait line across the length of the tube.
3) Using the ruler make a mark on the line 1/2 inch from one end of the tube, this is were the coil well start.
4) Using a small drill, make a hole on the previously made mark, also make another hole about 1/4 down from that hole, the two holes well be used to secure the end of the wire.
5) Unwrap a few inches of wire from the end of your spool of wire and feed the end through the first hole drilled in the tube.
6) Pull the end of the wire through the first hole a couple of inches and then feed it back out through the other hole, this well lock the end of the wire onto the tube.
7) Start carefully wrapping the wire around the tube away from the starting hole. The hardest part is to keep the windings tight and even.
8) At the fifth winding use the pliers to make a loop in the wire by holding the wire in the pliers and folding the two ends down the twisting the wire around once.
9) Continue to wind the coil and make another loop at wraps 10, 16, 24, 32, 40, 52 and 65 after the loop at wrap 65 there are no more loops but you have to continue to wind the coil until you have 80 wraps. These loops well become the taps in the coil in the finished circuit.
10) Once you have made 80 wraps drill two more holes, one on the line and one about 1/4" above it, right next to the previous wrap.
11) Cut the wire from the spool leaving a few extra inches of wire to feed through the holes.
12) Feed the wire through the first hole and back through the second, just like at the start and pull the wire tight to insure the windings are tight.
13) Measure the tube 1/2 inch from the end of the windings and cut off the excess tube so that the tube is even.

## Step 4: Making the Tapswitch

In this step we well make the pieces for the tap switch. The tap switch is used to select from the different sections of the coil using the loops/ taps made when we wound the coil. If you decide you do not want to make the tap switch from scratch you can use a rotary switch instead. Also in the next step I am going to show how to make the cats whisker detector, this was one of the first types of detectors invented for use in radios, it uses a piece of mineral, like galena or in my case iron pyrite, and a fine wire to act as a simple diode. If you do not want to make the detector by hand you can use a common 1N34 germanium diode available from Radio Shack instead.

To make the tap switch you well need:
- strip of thin copper or brass 3/8" wide
- one 2" long screw
- one 1" long piece of dowel
- one hex nut
- one washer
- super glue
- paint or stain and lacquer

Tools:
- tin snips
- drill
- metal file
- pliers
- paint brush

1) Using a ruler and utility knife score a line 3/8" of an inch from one end of you sheet of copper.
2) Using tin snips cut the strip out along the line and re-flatten the strip with a hammer on a hard surface.
3) Cut the strip to 1-9/16" long.
4) Mark the strip 3/8" from one end all the way across. At the other end of the strip opposite the end you just marked measure in from each side 1/16" along the top. scribe a line from the marks on the top to the line 3/8" from the bottom and cut along the line with tin snips, this tappers the pointer down to 1/4" at the top. See forth picture.
5) Use a file to clean up the edges and round the ends of the pointer.
6) Cut a piece of dowel 1/2" long and drill a hole 5/32" down the center.
7) Holding a the dowel in position on the pointer use a nail in the center hole of the dowel to make a mark and drill a 5/32" hole through the pointer at that mark.
8) Slide a washer over the 2" long screw and then slip the dowel and pointer on after. Using a small drop of super glue, glue the pointer to the dowel and thread the nut onto the screw and tighten the nut.
9) You can either paint the knob, stain it like I am doing or just clear coat it and keep it the natural color of the wood.

## Step 5: Making the Cats Whisker Detector

As mentioned you can omit this step in favor of a modern Germanium Diode instead, I have decided to make the detector from scratch to make the set more authentic. I well probably install a set of terminals so that I can use a diode as well if I do not want to fiddle with the Whisker.

I actually got the plans for this detector from the book, "The Boys first book of radio and electronics" by Alfred P. Morgan. This is a really great old book with loads of information on this kind of stuff with numerous plans for crystal radios, a tube radio and tube amplifiers, I would highly recommend this and any other book by this author if you can find them.

To make the detector you well need:

1 - 3/8" wide strip of copper 1-7/8" long
1 - piece of heavy gauge copper wire about 2-1/2" long
1 - spring from a worn out ball point pen
1 - binding post

Tools:

- pliers
- tin snips
- strait edge and utility knife
- drill and 5/32" drill bit
- file
- soldering iron and solder

1) Start by cutting a strip of 3/8" wide copper 1-7/8" long to make the crystal holder.
2) Mark and drill a 5/32" hole in the middle of the strip of copper.
3) Using a file on edge cut teeth into the ends of the strip of copper.
4) Using a large pair of pliers with jaws that are about 1/2" wide, hold the hold the strip of copper in the middle so that the strip is perpendicular to the jaws. Fold the two ends up.
5) Bend the serrated ends over to make a set of jaws to hold the raw iron pyrite.(see photos)
6) Take the spring from the pen and straiten out one end so that it is about 3/4" long and then solder the spring to the end of the piece of bare copper wire.

## Step 6: Making the Case

The case is made of 1/2" think by 6" wide boards, I am using Poplar on mine as it is cheap and accepts stain well.

To make the case you well need:

1 x 1/2"x6"x4' long board
1 x 3/8"x6"x2' long board
- glue
- nails
- finishing supplies, paint, stain, whatever

Tools:

- Saw, I am using a power miter box because I am lazy
- Hammer, again I am lazy so I am using a pneumatic brad nailer with 1" long brads
- Sanding block and sand paper, I use 220 because it well wear down to finer and finer grades as you use it so it leaves a nice surface for finishing.

1) The first thing that has to be done is to cut the boards to length to make the sides and front and back. You well need to cut 2 1/2"x6"x9" long boards for the front and back and 2 1/2"x6"x7" long boards for the two sides, also cut 2 3/8"x6"x7" long boards to be glued together for the bottom.
2) Next you need to glue the two sides and front and back together to make a box, the two side pieces go between the front and back not on the ends of the front and back.
3) Now would be a good time to use some wood putty to fill in the holes left by the nail set, or in my case the hammer of the pneumatic brad nailer.
4) To make the bottom you well need to glue the two 3/8" pieces that are cut to 7" long along the sides that are 7" long. Start by sticking a wide piece of masking tape, 1" is probably good enough, along the 7" long edge of one of the boards leaving it sticking out half way, see photo.
5) Butt the other piece of wood up to the first one and align the ends so that they are flush and stick the tape down to the other board while holding the two firmly together.
6) Once the tape is stuck to the other board flip the two over and fold them together so you can apply glue to the edges that well be stuck together.
7) Spread some glue to the edge of one of the boards where the seam well be and lay the two boards out flat again of a flat hard surface.
8) Push down along the seam to ensure that the two boards and even and all the excess glue squeezes out and wipe up the excess.
9) Put another piece of tape alone the seam on this side making sure that the seam is flat and even then place another board on top of the two being glued together and place a heavy weight on top of that to hold it down while it is drying.
10) After the glued has dried on the bottom, pull the tape off and trim it to length so that it fits inside of the bottom of the box and glue it in.
11) I also decided to make a lid for my prototype, I glued two boards together the same way as I did on the bottom and cut it to size so that it sets over the top of the box.
12) Next add some slats to the inside of the box to screw the panel to, if you are making a lid set the slats down 1" from the top, it not set them 1/8" from the top so that the panel well be flush with the top of the box.
13) Finish the box with what ever finish you desire, I chose to staining mine and then coating it with two coats if polyurethane, you could paint it instead which would be simpler.
14) Once the finish has had adequate time to dry, tape the top down to the top of the box in the orientation that is well be in when finished on the three sides that well not be hinged.
15) Using pieces of tape to hold the hinges in place, drill pilot holes for the hinge screws and install the lower screws. After the bottom half of the hinge is mounted pull the tape off and attach the upper half.
16) Remove the tape holding the top on and make sure the hinges do not bind.

## Step 7: Making the Front Panel

To make the front panel you well need

- some 1/8" Plexiglas
- graph paper
- pencil and ruler
- tape
- drill and 5/32" drill
- metal strait edge
- utility knife

1) Start by cutting the Plexiglas to size, the easiest way to do this it to use a strait edge and knife to score the Plexiglas and then to break it by firmly holding it over a sharp edge and snapping off the excess. If you are mounting the panel on top of the box make the panel 8" by 9", if you are mounting it inside of the box like I am cut the panel to 7" by 8".
2) Next you well need to figure out who you well want to have the panel laid out. To do this you well need to collect all of your parts so that you know who big things are and how they well have to be in relationship to everything else.
3) Next take your graph paper and draw a full size representation of the panel on the graph paper and use your parts as a guide to figure out where all of the holes well need to be drilled to accommodate everything. The only two measurements that are already determined are that the holes for mounting the coil have to be 3-1/2" apart and that for the tap switch you well need 9 evenly spaced holes around a center hole with a radius of 1-1/4". It also helps to have the coil and tap switch close together making it easier to wire the two together and keep the wires short.
4) Now make a photocopy of your plan and tape it to the front of the panel and use it as a guide to drill the holes in the panel. Note: Plexiglas can be tricky to drill, don't run your drill at too high of speed as it well melt the plastic to much and also don't use too much downward force when drilling as that well cause cracking. It is also a good idea to practice on a small scrap before hand so you can get an idea of what works the best.
5) After all the holes have been drilled you can paint the panel if you want, you can also leave it clear if you want to see the insides of the radio which is cool. Start by taking some fine sandpaper or a Scotchbrite pad and scuffing up the surface to be painted. Once the surface is evenly scuffed up clean it with dish soap and dry it thoroughly.
6) Paint the panel, I am using black spray enamel.

## Step 8: Assembly

Right now that all the pieces have been made it is time to put it all together.

Materials:

- all the screws, washers, nuts, solder lugs and other miscellaneous hardware
- the case, detector parts, panel, tap switch wiper ect

Tools:

- pliers
- 5/16" open ended wrench
- soldering iron and solder
- wire cutters and strippers

1) First we well start by assembling the tap switch.
a) Start by adding the screws for the tap switch, place a screw in the hole and add a solder lug to the back side and tighten it all down with a nut. Make sure to position the solder lug pointing to the center of the the circle.
b) Slide a washer over the end of the tap switch wiper and install the wiper in the center hole.
c) Slide another washer over the screw and add a nut tightening it down so that the wiper turns with a some resistance so that it well not lose its setting when in use. Slide a solder lug onto the screw and add another nut tightening it down to the other nut locking the two together.
d) Cut the excess screw off.

2) Installing the coil.
a) Install the 2" coil mounting screws through the front of the panel and secure them with nuts.
b) Solder short, about 3" to 4" long, pieces of wire to each of the 8 coil taps.
c) Solder the tap wires to the tap switch contacts starting with the first tap a the fifth winding in the first contact and progressing all the way around the tap switch until all 8 taps are wired.
d) The ninth contact of the tap switch is connected to the end of the coil along with a piece of wire that well be used later.
e) Solder a length of wire to the tap switch wiper.
f) Install the coil onto the coil mounting screws with a washer and nut on each side.

3) Installing the remaining components.
a) Mount the stereo headphone jack to the panel.
b) Next mount the crystal holder with a screw, solder terminal and nut. If you are using a germanium diode instead of the crystal holder install a Fahnstock clip instead, still using a screw and solder lug.
c) Mount the binding post for the cats whisker tightening down only lightly so that the binding post can be swiveled back and forth to help aid in setting the detector. Again if using a diode install a Fahnstock clip using a screw and solder lug.
d) Now using 6 6-32 1/4" long screws, mount the variable capacitors and turn the knob to make sure that the stator does not run into the ends of the screws, if it does you well need to place washers between the panel and the capacitor frames so that they clear.

4) Wiring!!!
a) First solder the wire coming from the 9th tap switch contact/ end of coil to the bottom of the binding post.
b) Glue the impedance matching transformer to the back of the panel between detector and the headphone jack and solder one side of the primary winding to the detector crystal holder.
c) Solder one side of the matching transformer secondary to both the ring and tip terminals of the stereo headphone jack. Solder the other end to the sleeve terminal.
d) Solder a wire to connect the frames of the two variable capacitors together. Also solder the unused end of the matching transformer primary to the one of the two capacitor frames. Solder the wire coming from the tap switch wiper to one of the capacitor frames as well.(see photo)
e) Solder a wire from the stator of the tuning capacitor C1, the one closest to the antenna and ground binding posts, to the antenna binding post. Solder another wire from the ground capacitor C2 to the ground binding post.

5) Final Assembly
a) Set the panel into the box onto the mounts and install the mounting screws.
b) Use glue stick to glue the dial faces to the front panel and install the knobs.
c) See next step on how to use the set.

## Step 9: How to Use the Radio

1) Start off by connecting up the antenna and ground. For the antenna you can use anything from a long piece of wire tacked up along the top edge of a wall to a nice long outdoor wire antenna. The ground can be any suitable ground connection, ie the center screw on a power outlet, a iron cold water pipe or an outdoor ground spike driven 5 feet into the ground.
3) Mount a small piece, about 1/4", of iron pyrite in the jaws of the detector and position the cats whisker so that it is touching the surface of the iron pyrite. If you are using a germanium diode install it in the Fahnstock clips with the band facing the antenna and ground binding posts.
4) Turn both knobs all the way to the left and select the 1st tap contact. Start turning the left tuning knob slowly to the right and see if you can find a station, if you find a station but it is towards the high end of the dial move the tap selector up one and turn the tuning knob down until you find it again.
5) If you are using the antique style detector and the signal is coming in very weakly you can try moving the cats whisker around on the surface of the iron pyrite until it comes in more strongly, this well take some trial and error until you find were it works best.
6) If you are receiving two stations at once and one is drowning the other out you can use the ground coupling knob to help single out one or the other.
7) Make a logbook of what settings brought in what stations, this well help finding the station again later.
8) Fiddle with it, it takes some practice to tune these kinds of radios and remember the only thing powering the radio is the radio waves received by the antenna so the signals well not always be that loud but a nice long antenna well collect more energy producing louder signals.
<p>I made my first successful crystal radio last Fall and plan to make a much nicer one (like this) as soon as I can. There is just something awesome about listening to one!</p>
Wow, this is really elaborate and dedicated! Personally I am not much of a technical person but I am sure a sucker when it comes to antiques. I always feel that they are so classy and makes me feel that I am able to time travel just my interacting with such antiques. However, I do not think I would be able to accomplish building such timeless radio on my own as it just seems too tough for me. But if I were to make one on my own I would most probably put some antique silver designs on it just to add on that vintage feel.
Outstanding! I will certainly use a lot of the information here when I build mine.
what's the purpose of the coil in the circuit?
You are very capricious. Congratulations on the project.
i made something like this out of a book but icant decipher any of the things i here! is there any way to make it louder?<br />
Radio Shack sells a small 9v amp you plug into the headphone jack. <br>Works Real Good. <br>
thanks!
VERY WELL DONE ! <br>There are schematics to be had for some of the most complicated crystal sets <br>complete with Wave Traps, Ferite wound coils, 600/44 Litz Wire, and lots of other things ! <br>There is even a DX Contest ! for AM Listening ! <br>I have built several of these sets and the best so far was a Push/Pull wired coil with 2 tunable tank circuits. <br>Check out midnightscience.com plenty info there. <br>Also, Crystal Set Society is another good source for AM DX'ing Contest. <br> <br>Great Ible ! <br>More please !
mabey ill just put the scanner in a nice looking box like that one an pretend like when i was a kid :O)
does the floor jack hold your table up
i wanted to build one but now i think buying might help me live longer lol
Excellent job, but how can you use low-impedance earphones with this set?<br />
carrier wave amplitude modulated draw creates an optical illusion!!!<br />
Dual 1T4 regenerative vacuum tube radio receiver =P<br /> <br /> The first tube is an RF amplifier, while the second serve as the regenerative stage.<br />
This has to be, so far, bar none, absolutely, positively, THE BEST Instructable that I have EVER been to. It is also the most professionally documented. The photographs are crisp and clear and are provided not only at the most important steps, but also many of the intermediate steps. The instructions are easily understood, easy to read, with proper grammar and correct spelling. It, in nautical terminology, “Blows all of those mint box instructables clear out of the water and sends them all to Davy Jones' Locker”. Ohm you certainly have done one “bang-up” job, you are the only instructor that I have subscribe to. This Instructable, in my not so humble opinion, deserves the “Grand prize of Grand Prizes award” if there is one.
Well, thank you very much :) I did get second place in the science fair contest, the winner did a very cool Rubin's tube.
Hey Ohm, what book is that? sounds interesting. :)
i have that book the the boy electrician
I finally got around to building a radio! For years, I knew how to build one, but didn't because I live in the city, and putting up a 100 foot antenna simply wouldn't be possible. But then, an idea came to mind. What if I made the coil big, REALLY BIG and had it serve a double purpose? So I took some pieces of wood about a yard and a half long and nailed them together to make the form. Then, I wound all of the stranded wire I had in my house around the form, and my coil was born. Unfortunately, I didn't have any variable capacitors or high Z (Impedance) earpieces, so quickly soldiered together a five minute transistor amplifier (Not push-pull or anything fancy, just a single transistor with a bunch of resistors), and for the headphones I used an old '60s telephone headset. Instead of the variable capacitor, I used a fixed 470pf ceramic disk one that I found lazing around in my parts box. Excited to put it all together, the whole project took about an hour and a half from idea on paper to working device. I'm pretty proud of my creation. I'll be sure to post some pictures soon...
I just built my second radio! I found an LM386 and cobbled together a short antenna, a loopstick from an old TV, and a rectifier diode for the demodulator (detector) and a small capacitor and connected it to an 8 ohm speaker. It sounds great! Pictures coming soon. I am currently working on a Tube Regen using 12dz6 pentodes. I promise I will write more.
I just finished the regen! Works great! Instructable soon. I also built a two tube IT4 radio. I also put up a 100ft antenna and made a 5 minute crystal set.
If you need to wind a coil quickly, stick the form into a lathe and just guide the wire along (wear gloves). Makes it really quick and (worryingly) quite fun. Great 'ible. AlexHalford
That works but it helps to have a way to count the winds, for that I use a micro switch attached to an old calculator with the switch soldered in place of the + button. I enter a 1 and turn it once by hand and it counts from there. Unfortunately with this particular coil being that it has so many taps you kinda have to wind it by hand.
Love the idea with the calculator. Also, you could time yourself with a stopwatch and compare that to the speed of the lathe (i tend to use 65 RPM for coil winding) to figure out how many you've done. AlexHalford
I used plexiglas for a reproduction radio panel once, but sprayed the back of the panel black. This made the front finish very smooth and shiny black, but scratch-proof - more like bakelite. I used white letters on black labelling tape for the control lettering.
Yeah I realized that I should have done it that way after I had already painted the front of the panel. Oh well I well remember that next time.
The holes in the top of the box looked like an upside down smile!!!
The great thing about crystal sets is that you can make most of the bits yourself (apart from the earphone, haven't managed that yet ;-). I have made my own capacitors (aluminium foil sheets in a book), my own detectors (various sulphide minerals including galena and molybdenite, even a rusty razor blade and pencil lead) and of course my own coils. If you do a search on the internet you will find an amazing variety of designs and approaches. It's a great hobby for those that live away from a horse racing station that swamps everything. ;-)
hi, i was just thinking about how to make an earphone by myself, so that the crystal radio will be entirely homemade. I think we can use the piezoelectric caracteristic of quarz to build that kind of earphone. i might try it someday ;)
I just found this one the web, <a rel="nofollow" href="http://josepino.com/other_projects/index.php?making-high-impedance-headphones.jpc">Making High Impedance Headphones</a> It shows how to make a set of high impedance phones out of an old set of modern headphones and two broken digital watches. Might be a good Instructable on it own.<br/>
thanks for the link... this is a really good idea to make such earphones ;) first of all i need to make a 1kHz sine oscillator to define the nominal impedance of this piezoelectric device.
...... i just calculated that to make a earphone of about 1kohm impedance at 1kHz with a coil and a magnet. You need a coil of about 160 mH... And i also calculated that using AWG48 wire you need to make a Multi-Layer coil of about 4cm diameter, 1cm height and 2cm wire-layers width... and that makes about 1600 turns of wire. 1600!! i think i am going to make the piezoelectric earphone like on your link, it is easier ;)
Excellent - now I can make the whole radio myself. Now, if I could make the wire..... ;-)
That is one problem I am having is there is one station that is real close to where I live and it is drowning out three other stations around it so I think I well have to make a wave trap for it as well which should work pretty good I think. I got an outside antenna installed and that has helped a bit as well, I did not do an instructable on it though, didn't feel like taking photos while on the roof in the 90 degree heat. I am also going to make a two tube amplifier for the set as well, I have all the bits just laying around, is that a good thing or bad :) I might do an instructable on the wave trap and the amp though just for fun.
at the antenna connection make a series resonant circuit to ground at the frequency of the offending station. it goes tearing to ground and the other stations are not affected. use a coil and mica variable cap(series) adjusted to the stations freq. good luck.
The is exactly what a wave trap does except that it used a variable capacitor allowing you to tune it to the desired frequency, I have also seen one that has a coil with a slider and variable cap making it even more tuneable.
i didn't mean to insult u. hope i didn't. ur already all over it. i said mica variable to save the 365 air variable for the main tuning. they're not getting any cheaper. the variable coil arrangement makes it very useful where a lot of am stations can be heard. wouldn't u know, u always want the waeker one. a fixed coil worked ok fr me. i only needed to get rid of 5000w ststion 600 yards away. good luck.
ooooooo I wish I had a 5000W station close by. think of the power I could harness from it using only a AM antenna, a bridge rectifier, and a capacitor!
i need to try a voltage doubler on the wave trap. i think i can drive a darlington pair audio amp. maybe more. i can see a battery charger in the works. here i go againnnnnnnnnnnnnnnnnnnnn.
ha.
A few things<br/>The higher the better for antennas (outside definitely) and a good ground (or even two or three seperate ones).<br/>The best coil I have tried so far was the mystery set coil: <a rel="nofollow" href="http://www.clarion.org.au/crystalset/mystery.html">http://www.clarion.org.au/crystalset/mystery.html</a><br/>which managed to keep the loud station within a small band of the tuning and then allowed me to hear some of the others (2 sometimes 3). So a bit of experimenting with the coil might give you better results for your area.<br/>TRIVIA: I have heard that some people living REALLY close to a transmitter have been able to use a crystal set to charge batteries (don't know how long that takes though).<br/>I'd like to see the wave trap so feel free to post that instructable when done. ;-)<br/>Also I forgot to mention that I used silver wire with the molybdenite. There's a site somewhere where someone has compiled a list of the mineral combinations that work. I'll see if I can find it again.<br/>As I mentioned there is just so much scope to this concept - it's great!<br/>
the wave trap is really simple. a coil and variable cap that runs between the ant connection and ground. this is a series resonant circuit. only 2 parts : a tank coil and cap the same as the main tuning. tune the trap to the offending station. it may take some tweeking but what doesn't?
That would actually be a tank circuit, and the premise is easily had on a search. Basically, it's a wide bandpass filter. Kudos to you, Eromanga. You are definitely headed down the old school path ;)
There is a variation worth exploring, one I did not see during cursory exploration of the various linked sites, a project I made as a boy, especially if you have a strong station nearby. You can add a second crystal receiver in the same box, tuned to the strong station, fullwave rectify its output to charge a polarized capacitor, use the capacitor to power a one-transistor audio amplifier. Resulting sound will fill a room. U.S.
my word thats brilliant.
Sam you are making it more complicated than it actually is. This radio should drive an audio amp as is. Using a ceramic capacitor to couple the circuits.
Looks Great ! However using fahnestock clips, for the antenna and ground connections, could add to the old timey looks
Well I got the amplifier done, here are a few photos that I took of it while I was testing it. Mind the mess, I have way to many projects/ hobbies. The first photo is of the whole thing being tested, had to remove the panel and connect the amplifier with jumpers as I have not put connectors on top yet. I am also using my power supply for the heaters, I still need to scrounge around for a battery holder to run them on. It works really well, definitely gets the job done, I can here a few more stations that I could not before and of course the local station is even more domineering over everything else, too bad the music station is hiding just behind it.