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 Post subject: Superboy's Foxhole Radio
PostPosted: Jul Mon 20, 2009 9:23 pm 
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Location: Columbia, SC, USA
Aside from radios, I also read and collect comic books. While reading an old DC comic I came across this:

Image

I thought you all might think it was as neat as I did so I posted it for your enjoyment. If you'd like the original you can order it here:

http://www.mycomicshop.com/comicbooks/item?IID=5284211

for 70 cents in very good condition! I plan to build this one just for fun. Kind of fun to be able to tie 2 of my hobbies together.

Terry

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 Post subject: Blue razor blade
PostPosted: Jul Mon 20, 2009 10:02 pm 
Silent Key

Joined: Nov Fri 28, 2008 4:45 pm
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Location: Near Fargo North Dakota USA
I have heard that you will need the blue razor blade. I have never tried one of these but have built several other crystal radios.


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 Post subject:
PostPosted: Jul Mon 20, 2009 10:14 pm 
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Since firearms are my other hobby, I bought some WW2 vintage Winchester and Marlin Firearms brand blue blades to build my foxhole radios with!

Terry

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 Post subject:
PostPosted: Jul Mon 20, 2009 10:16 pm 
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You could probably use a blued hacksaw blade instead of a blued razor blade, which I'm guessing would be hard to find.

Bob


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 Post subject:
PostPosted: Jul Mon 20, 2009 11:30 pm 
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sofaslug wrote:
You could probably use a blued hacksaw blade instead of a blued razor blade, which I'm guessing would be hard to find.

Bob


Actually, I found plenty of unused packs of blue blades on ebay pretty cheap. That's where I got mine. I paid a little more for mine as I wanted those specific brands.

Terry

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 Post subject:
PostPosted: Jul Mon 20, 2009 11:37 pm 
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Joined: Jul Mon 21, 2008 5:17 pm
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Location: SW Ohio
When I was in high school in the 60s, I built one of these. It's been so long I can't remember the type of razor blade. It worked great. Got me hooked on radio!!

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 Post subject:
PostPosted: Jul Mon 20, 2009 11:55 pm 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
Posts: 34328
Location: Sandpoint, IDAHO 83864
Sure wish I could say the same thing! My attempts at making a working foxhole radio were absolutely pathetic and then some. I was only 8 years old at the time, but it pretty darn near destroyed all the thoughts in my mind about becomming interested in radio.
Curt

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 Post subject:
PostPosted: Jul Tue 21, 2009 12:01 am 
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Location: Northwest Florida (Panhandle)
Terry:

The foxhole radio makes a great demonstration of semiconductor (of sorts) detection. There are many dissimilar materials which exhibit the same property as the blued razor blade, such as a junction of some metals and their oxide. I would not be surprised if you could receive a local station using an old penny and a shiny copper nail as the "crystal".


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 Post subject:
PostPosted: Jul Tue 21, 2009 12:26 am 
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Lots of interesting info on this subject here:

http://bizarrelabs.com/foxhole.htm

I recall the "All About Radio and Television" book when I was a kid, and building the foxhole radio. It is included on the above page.


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 Post subject:
PostPosted: Jul Tue 21, 2009 1:37 am 
Silent Key

Joined: Jan Thu 01, 1970 1:00 am
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Location: Sandpoint, IDAHO 83864
That book is where I got my idea of building a foxhole radio!
Curt

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(Connoisseur of the cold 807) CW forever!


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 Post subject: Winding the coil
PostPosted: Jul Tue 21, 2009 3:55 pm 
Silent Key

Joined: Nov Fri 28, 2008 4:45 pm
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Location: Near Fargo North Dakota USA
ImageI used to get so mad at winding coils. When I was 12 I made a Tesla coil out of carpet innards tube. It was a long process to wind copper to the top. And once or twice it all just loosed up as I had not thought of a way to hold it. (Tape would have worked). When it was done I got a furnace transformer and dowels wound with heavy gauge wire for the primary. It really did work.

Recently I built some crystal radios. I bought an erector set motor which turns really slow. I mounted it on a table top and used a push button switch on the floor to use my foot to turn the motor on and off. Then made large wood tapered pieces to fit into PVC pipe ends. This worked well in making a tight coil.


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 Post subject:
PostPosted: Jul Wed 22, 2009 12:32 am 
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Location: Park Hills, MO 63601
You don't need a "blued" razor blade. The "bluing" is simply a type of thin corrosion that protects the metal from further corrosion. There are a number of compounds that will produce the effect on various types of iron and steel. Heck, early firearms "bluing" was done with a process using charcoal. I would suggest that you use your foxhole radio to do some experimenting. Heavily oxidized steel would generally not be a good candidate for several reasons that I won't go into now. Let's just say that the detector works by creating a diode by allowing the tiny current to pass between the base material (razor blade) and the cat' whisker (safety pin/pencil lead) in one direction, but not the other. Ideally, this is done by using the natural properties of two dissimilar metals - but it has been shown to be more effective when one metal shows some fine crystalline structure, with a very small amount of "contaminant" in the matrix (like "blued" steel). I would suggest some hammer-forged steel that is very lightly corroded be tried for the "crystal" part of the detector. The cat's whisker need only be very fine at the contact point to prevent contact with multiple "crystals" in the matrix (they muddy the signal by having differing resonant frequencies) and reducing the resistance of a broad contact surface.

Sounds like fun. Good luck!

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 Post subject:
PostPosted: Jul Wed 22, 2009 1:39 am 
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Location: Dallas Texas
We've been makking crystal radios for the last three years in my science class. Of 150 radios constructed by my 8th grade students, we've only had three which we not able to make work. We've used all kinds of blades but have generally found that on the new blades, like razor knife blades, we have the best luck after degreasing them and heating them until they are nicely oxidized. We also have found that if we are unable to get a station, we can apply the pencil lead to the etching on the blade or the sharpened edge and almost invariable can pick up some kind of signal.


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 Post subject:
PostPosted: Jul Wed 22, 2009 1:11 pm 
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Joined: Jul Thu 12, 2007 9:36 am
Posts: 543
Location: Boston,Ma
Hey All,
Whenever this subject comes up I always give the same advice: use a diode FIRST to get the set going. THEN try the blade.

These types of dissimilar detectors can be very hard to get working properly, especially under marginal conditions.

I get concerned when folks try these as a first project because they might not get the results they seek (or ANY results at all !) and get turned off to the radio hobby (for no good reason).

And FWIW, the boys at Anzio (and all other GI's )would have used ANYTHING else for a det ,IF it were available .

K


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 Post subject:
PostPosted: Jul Wed 22, 2009 5:30 pm 
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Location: Cleona, PA
Often a piece of tarnished brass, bolt, nut, hinge, etc. will work when a catwhisker is moved around the surface. Also a piece of galvanized tin when heated in a flame makes different sensitive spots.

Cultural / historical note: Superboy's article has nothing at all to say about not cutting yourself on the razor blade. We all knew what to do then and to take responsibility for it! A comic book today would NEVER have anything like that in it.

Lawyered to death in the USA,

Reece


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 Post subject:
PostPosted: Jul Wed 22, 2009 5:33 pm 
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wrnewton wrote:
Often a piece of tarnished brass, bolt, nut, hinge, etc. will work when a catwhisker is moved around the surface. Also a piece of galvanized tin when heated in a flame makes different sensitive spots.

Cultural / historical note: Superboy's article has nothing at all to say about not cutting yourself on the razor blade. We all knew what to do then and to take responsibility for it! A comic book today would NEVER have anything like that in it.

Lawyered to death in the USA,

Reece


Since Superboy didn't have to worry about getting cut, the thought probably never occurred to him.

Bob


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 Post subject:
PostPosted: Jul Wed 22, 2009 8:13 pm 
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Location: Bloomington, MN, 55425
Well that comic book site sure blew a couple of hours out of my day. Those photo covers of the fifties westerns
really bring back the memories. Thanks Terry.


-Phil


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 Post subject: Razorradio
PostPosted: Dec Tue 22, 2009 8:45 pm 
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Joined: Dec Mon 21, 2009 4:56 pm
Posts: 16
I've built a few of these razorblade crystal radios with good success.

It's important to remember to have a good ground. A metal rod or pipe driven 3 or 4 feet into the ground works good. A cold water pipe is OK, but usually inconvenient. If you're real close to an AM station, you may not need the ground.

An antenna that's 40 to 100 feet is recommended.

Most important, make certain that you have the right headphones.
Most of the earphones and headphones they make today are low ohm. You need an old style 1500-3000 + ohm headphone, a piezo unit, or crystal headphones for a crystal or razorblade radio. You can even use a musci disc or a noise disc from a greeting card. Just get rid of the "printed circuit" and hook the two wire from the disc up to wear the headphones go on the radio.

I was able to get two or three stations on the one I built when I was in high school. However, most people say they only get one station.

I've used a 150 year old penny as a detector. It gave very weak volume, but it worked.


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 Post subject:
PostPosted: Dec Tue 22, 2009 10:16 pm 
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sofaslug wrote:
Since Superboy didn't have to worry about getting cut, the thought probably never occurred to him.

Bob


Why would SuperBoy need a crystal radio anyway??? I'm almost certain some part of his anatomy received RF..... :lol:

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 Post subject:
PostPosted: Dec Wed 23, 2009 1:36 am 
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Location: Marshall Mn
Razor knife blades in school :shock: I have nothing against it as it is for science and radio. I just wondered about zero tolerance policies.
I figured by now kids had to use a plastic knife to disect a frog :lol:

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