EXPERIMENTAL CRYSTAL SETS
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If you have built my basic crystal radio and would like to try another one with more volume, I would like to describe another set with a simple transistor amplifier. The front end of the receiver is the same as the basic crystal radio circuit, The only extra parts you will need are an electrolytic capacitor 1uf, 1 mega ohm resistor and a BC 108 or BC 109 NPN transistor.
You can build the circuit with chock block connectors as before or you may like to try the drawing pin style of construction as I have done, This uses a piece of soft wood for the base but unlike before instead of chock blocks we will insert drawing pins into the base board. You can then get your soldering iron and tin the top if the drawing pins until the solder has melted all over. When you want to insert a component you only need to melt the solder on top of the drawing pin to make a good electrical contact. When you start the coil wind 40 turns and make a tap, You do this by making a small loop, Then twisting the wire together, Scrape off the enamel and tin it with solder, Wind another 40 turns. Then simply wire the circuit as in the diagrams, Make sure you have the transistor the correct way as it can easy be damaged. It will still require a long wire antenna and good earth.
When you have finished check your wiring and then plug the PP3 9 volt battery in, you will notice a big increase to the volume, It is much louder than the Basic crystal set, there is enough volume to drive a standard set of 16 ohm magnetic headphones or even a 64 ohm loudspeaker, When I used my high impedance headphones some stations came in too loud and I had to off tune them a little for comfortable listening. Remember when finished to remove the battery or you may like to wire a toggle switch in line for the on/off.
CIRCUIT
