The AM Forum

Has anyone built a foxhole radio that actually works?...I would enjoy hearing about it and perhaps seeing a picture.....I built this foxhole radio several years ago and couldn't find a BLUE razor blade for the detector.....It works with the SS blade but not well at all....All I can hear with it is my own signal from my Gates on 160 M...I was digging thru some junk today and found this package of OLD GOLD blades.....They are Blue steel...just the right kind...I'm gonna make another f-hole radio now but I'm gonna make a larger toilet paper roll size coil and use the blue blade...Any other suggestions from successful builders would be appreciated..There is a 50 KW station, KGA ,25 miles from me in Spokane, WA that I should be able to pick up...Big DX...

Steve,

Very nice construction,  you either have too much time on hand or you're expecting an invasion.

I remember these "fox hole" radios many many years ago, don't remember if I ever made one.

Keep us posted on your progress. 

Fred

I made one when I was 8 and I didn't have a blue blade either, just used a regular one.  I got one station.  It helps to have a good ground and about 100 feet of wire, and a pair of crystal phones would be preferable but not mandatory.  I didn't have any and used my Cannon-Ball "Chief" phones.  Lots of fiddling around on the blade to find a "sweet spot."

Built them in the 50's, before I could afford a 1N34 crystal diode.  Not nearly as efficient as a germanium diode, but hey they did work.  If I remember correctly the so called "sweet spot" was right at the edge of polished blade surface and the blue metal.  Have fun, it will be a rewarding experience.

yes, they work great, try a dirty old copper penny, like from the 30's or 40's... copper oxide a decent semi conductor. The pencil lead has to be a real lead pencil... ROHS??

Real Lead?...Graphite? What else is used in pencils???  Fun stuff...I want to see if I can hear KF7EH in Spokane on 160 AM...

These radios may have been more effective during and just after the war in Europe, as there were quite a few Megawatt level broadcast stations, unlike here.  When I built mine I used the wire from the CRT yoke of a trash pile Tv set.  I didn't know about winding the coil in a solenoid fashion and just scramble-wound it, but it still worked. 

You can 'blue' a regular blade over a flame, forming a blue oxide layer.  Also try a fools gold (iron pyrite) crystal for shortwave sets. The spring from a ball point pen makes a good cats whisker too use the gold ones they are phosphor bronze.  They work very well.  I haven't built a crystal set in a long time but they were 'da bomb' at the time. I still have an old set of 'cans' to listen to them with.
Spiderweb coils were pretty cool looking too come to think of it.

Yes, back in the 50's and prior, you could get pencils without the restrictions of lead content in the finishing process of the pencil. Of course today a lead pencil is a historic name carry over, no lead in the pencil of today, as you noted, graphite. Should work as well.

Very cool, I built one in 1961 or 62. Then my parents bought me a crystal radio kit. By '64 I was doing tubes

Steve,
Remind me some night on 160 to dig out the x'tal related crap.  I'll haul it over next shooting trip.   

Steve, I built one years ago...still have it somewhere.  I remember being so damned frustrated tying to get detection with the lead and blade that I thought something else was defective.  I put in a diode instead and pulled in LOTS of stations.  Never did get that lead/blade thing to work.  Maybe I will give it another try.

Chris.

I built one of these when I was 10. The enameled wire was recovered from a pair of discarded model railroad switch machines contributed by my dad. The razor was a standard double edge "safety"razor. The piece of graphite was held to the side of a safety pin pointed part by means of several wrappings of copper wire. The safety pin was bent so that suitable pressure was made between the graphite and the razor's ground edge. Thumbtacks held everything to a small piece of pine board and provided terminal connections. The tuning capacitor was made from several foil gun wrappers with wax paper for the dielectric. Tuning was achieved by a slider against the side of the coil where sandpaper had removed the enamel. "Alligator" clips for ground and aerial connection, were made from spring action clothes pins with opposing thumbtacks. A crystal earphone was used for the receiver. Best reception of the local radio station (WGLI in Babylon, NY) was achieved by connecting the ground terminal to the kitchen faucet and the "aerial" to the finger stop of the kitchen telephone dial.  The signal was loud enough to be heard with the earphone lying on the counter-top. All were amazed that it worked better than the once unbroken, "Rocket" crystal radios that privileged older siblings had gotten for last Christmas.

I believe that the "crystal" detector was formed by the microscopic points of steel (Iron) in contact with the carbon crystalline structure within the graphite.

Next was modifying discarded, low voltage vacuum tube car radios.

Rob,
I did my detector the same way. Then I got my Dad to build a galena mount from a short length of copper tubing with a jack screw on the side. There was no galena in the back yard so I never got a chance to use the mount. He cut two slits in the tube and bent them out to make a flange so I could bolt it down. then the jack screw came in from the side to hold the magic rock. I was going to reuse the safety pin without the pencil lead. I don't think I had a cap across the coil.
That little red rocket radio was pretty cool, I also had one.