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CRYSTAL
SETS 1
Introduction What
- Why - How
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What They Are, Why They Came Into Being and How YOU Can Build Your Own CRYSTAL SET!
What
are Crystal Sets? I am glad you asked! It is a fascinating subject
dating back to 1920 when Marconi first started experimenting with radio
broadcasting from his station 2MT in Chelmsford.
The earliest listeners to Marconi's experimental radio programmes would have mainly used the most basic of radio sets called a Crystal Set. Companies such as the W.G Pye began producing early radio sets in 1921 which used electronic components called 'valves', the forerunner to today's transistors and silicon chips). These glass valves could be arranged to amplify the weak radio signal to make them louder - enough to operate a loudspeaker. However these radios were expensive and needed electricity or bulky lead acid batteries to operate.
THE MAGIC OF A CRYSTAL SET
The crystal set was popular during the 1920's and 30's because it was cheap to buy, much cheaper if you built one yourself, perhaps only a few shillings. Additionally a Crystal Set did not require electricity or expensive batteries, however it could only provide enough volume for headphone listening, and if it was situated in an area of low signal strength the listener would also require a very quiet room as the volume would be low. However In the 1920's hearing voices and music from a station miles away with no wires (hence the term Wireless) really was a magical experience! Listeners in the early twenties were also tinkerers and experimenters, trying different designs of crystal set in an attempt to get the loudest and clearest reception.
Since crystal sets have no batteries and no mains power, they rely entirely from the electrical energy developed between the aerial an earth connections - producing sounds as if by magic.
The crystal set had to be carefully tuned into the station by making adjustments to a tuning coil and condensor, these early crystal sets had the added complication of using a 'Cats Whisker' as the detector. The detector converted the radio waves received from the radio station into an audio wave that could be heard in the headphones. The Cats Whisker was a fine wire that rested onto a piece of galena, the crystal, and had to be very finely adjusted to obtain the loudest and clearest sound. Once the 'sweet spot' was found it was important not to move it, it would be very frustrating if someone bumped into the table and dislodged it!
To work at all a crystal set requires a very large aerial, but this is nothing more than a long piece of wire, perhaps 20 to 50 yards of insulated copper wire, hung outside around a garden between poles or trees, or even around the loft space. For the aerial to be effective it needs to be balanced with an earth. An earth is simply a copper rod or pipe about one yard long driven into some soft damp earth with a mallet. At the top of the pipe is fitted a jubilee or hose-clip to which is attached a length of insulated copper wire which is then fed into the house, along with the aerial wire, to the room where the crystal set will be operated and connected to the set's terminals.
It is quite possible to build your own crystal set. In its very simplest early form a crystal set consisted of a coil of wire, something called a 'detector' and a pair of very special headphones.
THE CONSTITUENT PARTS
The coil of wire is called a Tuning Coil, and the number of turns of wire on the coil determines the wavelength (frequency) that the set is tuned into.
The Detector converts the radio wave received into an electrical wave that is suitable for the headphones to, in turn, convert into soundwaves that can be heard by the human ear. Modern detectors are called diodes and are more efficient than early detectors and cats whiskers. Diodes are readily available and cheap.
The headphones have to be of a very special type called high impedence headphones. Because there is no additional power source in a crystal set the current generated in the circuit is tiny - miniscule in fact. Ordinary low impedence headphones, such as Walkman headphones, would present a virtual short circuit to the crystal set allowing the tiny signals to drain away to earth & consequently producing no sound - not very useful!
High impedence headphones, on the other hand, reduce or impede the flow of current down to earth, in effect saving the tiny signals to produce sounds from the headphones that we can then hear.
There is a problem however, these high impedence headphones that were so readily available in the 20's and 30's are no longer available - only to be seen in museums. All is not lost though, today we can obtain a special earphone called, appropriately, a crystal earpiece very easily and cheaply.
EXCELLENT RESULTS
Almost certainly when building a crystal set today a crystal earphone will need to be used. A crystal earphone is not quite as good as the old high impedence headphones as it is not quite as sensitive and therefore not quite so loud, however todays transmitters are much more powerful than those of the 1920's and so really excellent results are very often obtained - just don't expect to hear everything that you might on a top quality portable radio!
Crystal sets are fascinating because they are so simple to build, and because there is no power required they remain magical to this day. I have built several over the years, with differing designs, and if you'd like to build one yourself, it's easy, and I have described some circuits in part 2 with some more experimental ideas in part 5.
I have a crystal set that receives BBC Radio 4 on longwave and 3 local stations and 3 national stations on medium wave and another that also receives shortwave stations. Not bad for radios with no battery or other power - and such as set could be very useful in an emergency.
PART 2 >>>
PRACTICAL DESIGNS TO
BUILD YOUR OWN CRYSTAL SET!
Having difficulty in finding components? I am adding some ideas for component sources here.
Sources For Older Components
The earliest listeners to Marconi's experimental radio programmes would have mainly used the most basic of radio sets called a Crystal Set. Companies such as the W.G Pye began producing early radio sets in 1921 which used electronic components called 'valves', the forerunner to today's transistors and silicon chips). These glass valves could be arranged to amplify the weak radio signal to make them louder - enough to operate a loudspeaker. However these radios were expensive and needed electricity or bulky lead acid batteries to operate.
THE MAGIC OF A CRYSTAL SET
The crystal set was popular during the 1920's and 30's because it was cheap to buy, much cheaper if you built one yourself, perhaps only a few shillings. Additionally a Crystal Set did not require electricity or expensive batteries, however it could only provide enough volume for headphone listening, and if it was situated in an area of low signal strength the listener would also require a very quiet room as the volume would be low. However In the 1920's hearing voices and music from a station miles away with no wires (hence the term Wireless) really was a magical experience! Listeners in the early twenties were also tinkerers and experimenters, trying different designs of crystal set in an attempt to get the loudest and clearest reception.
Since crystal sets have no batteries and no mains power, they rely entirely from the electrical energy developed between the aerial an earth connections - producing sounds as if by magic.
The crystal set had to be carefully tuned into the station by making adjustments to a tuning coil and condensor, these early crystal sets had the added complication of using a 'Cats Whisker' as the detector. The detector converted the radio waves received from the radio station into an audio wave that could be heard in the headphones. The Cats Whisker was a fine wire that rested onto a piece of galena, the crystal, and had to be very finely adjusted to obtain the loudest and clearest sound. Once the 'sweet spot' was found it was important not to move it, it would be very frustrating if someone bumped into the table and dislodged it!
To work at all a crystal set requires a very large aerial, but this is nothing more than a long piece of wire, perhaps 20 to 50 yards of insulated copper wire, hung outside around a garden between poles or trees, or even around the loft space. For the aerial to be effective it needs to be balanced with an earth. An earth is simply a copper rod or pipe about one yard long driven into some soft damp earth with a mallet. At the top of the pipe is fitted a jubilee or hose-clip to which is attached a length of insulated copper wire which is then fed into the house, along with the aerial wire, to the room where the crystal set will be operated and connected to the set's terminals.
It is quite possible to build your own crystal set. In its very simplest early form a crystal set consisted of a coil of wire, something called a 'detector' and a pair of very special headphones.
THE CONSTITUENT PARTS
The coil of wire is called a Tuning Coil, and the number of turns of wire on the coil determines the wavelength (frequency) that the set is tuned into.
The Detector converts the radio wave received into an electrical wave that is suitable for the headphones to, in turn, convert into soundwaves that can be heard by the human ear. Modern detectors are called diodes and are more efficient than early detectors and cats whiskers. Diodes are readily available and cheap.
The headphones have to be of a very special type called high impedence headphones. Because there is no additional power source in a crystal set the current generated in the circuit is tiny - miniscule in fact. Ordinary low impedence headphones, such as Walkman headphones, would present a virtual short circuit to the crystal set allowing the tiny signals to drain away to earth & consequently producing no sound - not very useful!
High impedence headphones, on the other hand, reduce or impede the flow of current down to earth, in effect saving the tiny signals to produce sounds from the headphones that we can then hear.
There is a problem however, these high impedence headphones that were so readily available in the 20's and 30's are no longer available - only to be seen in museums. All is not lost though, today we can obtain a special earphone called, appropriately, a crystal earpiece very easily and cheaply.
 A commercially made crystal set from around 1940. There is no variable
tuning capacitor
(condenser) in the above design. The capacitor is a fixed
component and tuning is achieved by varying the coil inductance
with the rotating switch. The detector is a galena crystal,
seen at the top of the panel. A pair of high impedence magnetic
headphones can just be seen to the right of this shot. (photo
sent in by our reader Krysatec in Czechoslovakia - thanks!)
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EXCELLENT RESULTS
Almost certainly when building a crystal set today a crystal earphone will need to be used. A crystal earphone is not quite as good as the old high impedence headphones as it is not quite as sensitive and therefore not quite so loud, however todays transmitters are much more powerful than those of the 1920's and so really excellent results are very often obtained - just don't expect to hear everything that you might on a top quality portable radio!
Crystal sets are fascinating because they are so simple to build, and because there is no power required they remain magical to this day. I have built several over the years, with differing designs, and if you'd like to build one yourself, it's easy, and I have described some circuits in part 2 with some more experimental ideas in part 5.
I have a crystal set that receives BBC Radio 4 on longwave and 3 local stations and 3 national stations on medium wave and another that also receives shortwave stations. Not bad for radios with no battery or other power - and such as set could be very useful in an emergency.
PART 2 >>>
PRACTICAL DESIGNS TO
BUILD YOUR OWN CRYSTAL SET!
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Having difficulty in finding components? I am adding some ideas for component sources here.
Sources For Older Components
LINKS BOWOOD ELECTRONICS - A friendly, helpful and very speedy source for your electronic components at prices that won't frighten your wallet! The MK484 IC (the ZN414 replacement) is available from here. Simple crystal set receivers used by soldiers during the war and by prisoners of war (P.O.W.'s). THE FOXHOLE and P.O.W RADIOS PAGES WITH ARTICLES BY RADIO EXPERT FELIX SCERRI: High Quality AM Receivers: http://www.crystalradio.net/scerri/index.shtml http://www.crystalradio.net/ http://www.xtal-sets.com/ Hi Fi AM Receiver Designs: http://sound.westhost.com/articles/am-radio.htm OTHER ARTICLES ESP by Rod Elliot - "Mad as Hell" & lead free solder directive: http://sound.westhost.com/madashell.htm ESP by Rod Elliot - CFL's (Compact Fluorescent Lamps) http://sound.westhost.com/articles/incandescent.htm . |
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An old fashioned style detector that is
housed in a glass tube. The point of the cat's whisker touches the
crystal (galena) on the left & is adjusted with the black handle. |
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 An illustration of a modern diode which
is often encapsulated in glass and is about 7mm long. Above is
the
electronic symbol for a diode.
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