Gillette Blue Blade Crystal Radio Detector Kit
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Gillette Blue Blade Crystal Radio Detector Kit:
Go here to watch a clip on how to build this razor blade detectorRazor blade has been dulled to protect the builder.
Gillette Blue Blade Crystal Radio Detector
During WW2 the boys on the front used this blue razor blade idea that Cornell came up with
to listen in on the news and music.
Gillette came up with an idea to blue coat his blades to keep them from rusting
and as it turns out they rectify because of it with the combination of the carbon pencil lead.
Must have been a stroke of genius on Cornell's part to think of such a wild idea.In practice the way it works is you move the pencil lead over the lettering and the stations start coming in
and it just about works like a galena detector of the 1910 era because when you move the lead around you
can sometimes change stations or make the one you want clearer.
I personally built the blade radio in 1957 and again in 1962 for an electronic class project.
When I went to the Library one day i was looking around at electronic books and ran onto
a book on how to build the razor blade radio. could have been written by Cornell I don't know
I latched onto it and knew I could build it, it was fun!The razor blade supplied is a genuine 1930's blade as used by Cornell to build his radio.As can be seen in the second picture the lead is wrapped on with
silver plated copper wire and super glued to the safety pin and with
care should last a lifetime. in this kit
1 razor blade
1 safty pin with pencil lead attached
3 needed to make this a working radio
- A 300uh coil like 60 to 100 turns on a 3" diameter form.
- you can design your coil here Professor Coyle coil calculator
- pair of headphones or a high impedance crystal earphone.
- piece of wood like in the clip 6X7X3/8 or 1/2"
- 12"X1/8" brass rod used as a swip'er on the coil to tune the radio
- 60 to 100 feet of wire for an antenna
- more screws and brass binding posts like i have on another page
- or you can buy some fanstock clips.
- a ground to a metal water By USPS first class mail.
If you buy more than one kit shipping will be adjustedPayment by Paypal
Thanks for looking
Using professor Coyle's coil calculator a coil like used in the very antique crystal radios with no variable capacitor you rely on 15 to 20pf of capacitance that's built into the coil because the wire is close wound.
and what it comes out to is a 4" dia coil 7" long with 212 turns to make it down to around 700khz.
with no large capacitance you end up needing a huge amount of inductance.
what i do here is put small capacitors across the coil such as 100 to 500pf trying different ones,
this way the coil does not have to be so big and you can get down to the very low frequency radio
What the radio company's came up with for a final coil capacitance combination to cover the whole
band is a variable capacitor of 15 to 365pf and a coil of 240uh.
Also use the larger wire if you can, the larger the wire the better the "Q" of the coil.
if you have the cash to do it Litz wire is the only way to go, 600/46 Litz will get you somewhere
around 1000 "Q", and the Q gives you better selectivity and louder signals,
antennas can not be too long for a razor blade radio, the longer the better
up to say 234 feet that would be 1/4 wavelength for 1000kc the middle of the AM band.
the formula for end fed antennas is "length feet = 234/frequency
a dipole would be "length feet = 468/frequency................
A crystal radio operates on the signal strength only and the stronger the signal to the radio from the
antenna the louder it sounds.
so the more wire you can get up the better they work.
but on the flip side of all this if you can put up a full length antenna the stations
start to pile up on top of each other so then for this radio setup you need the best
selective radio circuit you can come up with.
I wont put it up here anymore i have my reason but if you want to send me a note through
and i will send you a diagram i re-designed from world widely accepted as the best circuit
available for a crystal radio.
It uses 2 diodes and separate antenna and receiver circuits inductance coupled so not to load up the
Headphones or speakers
Seems its real hard to come up with a decent pair of headphones,
so hears a trick someone came up up i cant lay claim to it, but use a battery or wall power
computer speaker to listen in ,
cut off the 3.5mm plug off the end of the speaker PC connecting cord
and strip back the outer covering, the wires have 2 types, plastic covered or varnished.
the plastic will have a copper shield around two wires the shield both of them can be twisted together and
the 2 wires you strip them and twist together.
then connect the 2 twisted together wires to the headphone posts or clips.
The varnished wire type has colored varnish.. strip with a knife the colored off all wires and
twist together the green ones and the other 2 together and connect to the crystal radio.
Or you can buy a stereo 3.5mm jack and wire that up and not do any cutting.
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Gillette Blue Blade Crystal Radio Detector Kit: