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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 28th Aug 2014, 1:53 am   #1
Stylo N M
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Default Razor Blade Diode

Hi,
We had a bit of fun this evening with something I saw recently on YouTube, with a razor blade and a small portion of pencil.

The pointed end of an opened up safety pin was pushed firmly into one end of the pencil, making contact with the lead, and the pointed end of the pencil lead was lightly touching the razor blade. All held in place on a block of wood with push pins. The razor blade must be partly oxidised first in a gas flame, and a wire attached to the end of the razor blade and the safety pin.

Remove the diode from a crystal set and wire the experimental razor blade diode into place, move the point of the pencil around the blue areas of the blade until a signal is heard.

Best results are obtained by using a pair of high resistance headphones but I have heard a signal in crystal earpiece as well, although extremely faint. It's a bit finicky but fun and it works!

Paul.

Last edited by AC/HL; 28th Aug 2014 at 3:06 am. Reason: Readability
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Old 28th Aug 2014, 3:12 am   #2
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Default Re: Razor Blade Diode

Many things can be, and were, used as detectors in the early days. Also in POW camps by all accounts. Coke (as in coal) and rusty metal were two amongst many.
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Old 28th Aug 2014, 8:01 am   #3
Alan Stepney
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Default Re: Razor Blade Diode

When I was at college we had a task of making a crystal set.
All we were given was a pair of headphones, unlimited wire, and we then had to make everything else.

My detector was a lump of coal, but some guys did use razor blades (the old blue blades work best) and one can find descriptions of sets using them, often listed as "fox hole radios".
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Old 28th Aug 2014, 8:05 am   #4
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Default Re: Razor Blade Diode

This was a problem with Co-Ax type plugs aerial plugs that had been subjected to damp and oxidation. Random signals would be demodulated at the input socket by the oxides developed between the inner pin of the Co-Ax plug and the TV receivers aerial input socket and cause all sorts of interference, odd patterns and noises on sound. J.
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Old 28th Aug 2014, 9:47 am   #5
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Default Re: Razor Blade Diode

Quote:
Originally Posted by Alan Stepney View Post
My detector was a lump of coal, but some guys did use razor blades (the old blue blades work best) and one can find descriptions of sets using them, often listed as "fox hole radios".
A lump of coal is quite usable as a detector: look for a bit that has gold/silver speckles of Iron Pyrites [fool's gold] in it and touch the cat's whisker [a bristle from a wire-brush is good!] on the different speckles until you fid one that rectifies.

I remember making such detectors in my teens - a good way to make the 'bulk' connection to the bit of coal is to get a metal screw-cap from a bottle and use a plug of steel wool shoved inside it then embed the piece of coal into the wire-wool.

Only problem with fool's-gold-detectors is that they do tend to lose effectiveness as the fool's gold oxidises - you need to split a new lump of coal every few days to get fresh detector-material.
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Old 28th Aug 2014, 11:02 am   #6
Radio_Dave
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Default Re: Razor Blade Diode

Here's my copy of a foxhole radio, with a Gillette Blue razor blade. It works when the pencil lead is tickled over the etched writing on the blade. David
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Old 28th Aug 2014, 1:15 pm   #7
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Default Re: Razor Blade Diode

Mine wasn't as neat as Dave's but this is similar to one of the very first radio's I made. Wire from a scrap transformer and an old razor blade. I was surprised when I heard the 'Home Service' (now Radio 4) coming through on some surplus headphones.
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Old 29th Aug 2014, 2:58 am   #8
AC/HL
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Default Re: Razor Blade Diode

One off-topic post moved here: https://www.vintage-radio.net/forum/...870#post702870
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Old 31st Aug 2014, 2:45 am   #9
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Default Re: Razor Blade Diode

The detector for an xtal radio can be made of a lot of things.
Here, the most common was a chunk of Galena ore (lead ore) embedded in either Whites metal, solder or whatever the maker decided to use.

A piece of Fools Gold, iron pyrite should also work, as well and most any metal xtal.
I bought several different metallic xtals at a rock shop in Colorado on my trip there with Jillian before she was killed. Right now I am looking at a fist size chunk of pyrite and one of copper ore that I got there

I will hook them up and see which one works the best.

Carborundum will also work, but IIRC, it requires a battery voltage to work best.
I suspect a lump of copper pipe, copper bolt, or whatever salvaged from the beach and heavily coated with copper sulphate/corrosion should also work. I suspect that even a piece of rusty iron may work.

Some company here in the States is also selling "Foxhole Radio Kits", as I ran into it while looking for other items on the 'net.

Back in my servicing days, I found several cases of the local radio station coming into amps from slightly corroded RCA type connectors, and one from a corroded solder joint. ( The station was literally 1/2 mile across the bay from some of these problems)
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Old 31st Aug 2014, 3:32 pm   #10
Stylo N M
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Default Re: Razor Blade Diode

Hi,

Yes I'm very quickly discovering that many strange objects do indeed detect, including a rusty old file and a rusty hacksaw blade. I did try the coke idea when i was a lad, but i couldn't get that to work at time but I know it does work.

Paul.
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Old 31st Aug 2014, 6:03 pm   #11
Alan Stepney
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Default Re: Razor Blade Diode

Galvanised wire fence works too.
Especially if you find a rusty part.
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Old 31st Aug 2014, 6:26 pm   #12
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Default Re: Razor Blade Diode

Zinc and/or Tin junctions can be used to form an amplifier !

http://www.sparkbangbuzz.com/els/znrfamp2-el.htm

Same goes for Iron Pyrites [Fool's Gold] which can - with external power - be an oscillator.

http://www.sparkbangbuzz.com/els/iposc-el.htm
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Old 31st Aug 2014, 7:15 pm   #13
Stylo N M
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Default Re: Razor Blade Diode

Hi G6T anuki,

Yes that fool's gold appears to be quite clever stuff

Paul.
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