How to Make a Crystal Radio Louder

Your crystal radio probably won't be as loud as one of these.

Adding a basic amplifier circuit to your crystal radio allows multiple people to listen at once, by replacing the standard high-impedance, low-volume standard earphones with a loudspeaker. Although crystal radios do not require batteries, this amplifier circuit will require a small battery. This method of amplification is not designed to reduce the interference that is a natural result of the radio's high bandwidth. This is solely a basic means of amplification and an alternative to the limitations of earphones.

Things You'll Need

• 9-volt battery
• Connector with leads for 9-volt battery
• Output transformer (1,000-ohm primary, 8-ohm secondary)
• .12 uF Mylar capacitor
• 15 uF, 10-volt capacitor
• .15 uF disk capacitor
• 150-ohm, 0.5-watt resistor
• ECG 129 PNP transistor
• SPST switch
• 3-inch 8-ohm speaker
• Solderless breadboard
• Jumper wire kit (22-gauge with alligator clips)
• 22-gauge wire

Instructions

1. 

   The transistor is the key to amplifying your crystal radio.

   Remove the earphones from the radio circuit and leave a few inches of wire on both sides to work with. Strip back some of the insulation for the new connections. Connect the positive side of the earphone section to the base (B-side) of the transistor. The emitter (E-side) goes to the 150-ohm resistor, with the 15 uF capacitor connected across the resistor.

2. 

   Capacitors store electricity and are an important part of almost any circuit.

   Ground one side of the disk capacitor and connect the other end of the resistor in Step 1 to the same ground circuit. Connect one end of the .12 uF Mylar capacitor to the wire between the base side of the transistor and the positive earphone side (from Step 1), and the other end to the same ground circuit.

3. 

   Switches allow you to turn current on and off and come in many shapes and sizes.

   Connect the other side of the disk capacitor to the transformer and connect the collector (C-side) of the transistor to the same wire, between these two points. The 8-ohm side of the transformer goes to the speaker and the other end is connected to one end of the switch.

4. 

   A 9-volt battery provides all the power you need to amplify your crystal radio.

   Attach the 9-volt battery connector to the battery. Connect the positive terminal's lead to the other end of the switch and ground the negative terminal. Ground the other side of the earphone circuit. It is preferable for all grounds to come together at a common point on the chassis.

5. 

   The appearance of your finished amplifier circuit could look something like this.

   Turn on the radio, flip the switch on the amplifier circuit and enjoy your crystal radio.

References

• Science Buddies: Electronics Primer: Terms
• "Electronics Projects for Young Scientists"; George Delucenay Leon; 1991

Resources

• Science Buddies: Electronics Primer: Use a Breadboard to Build and Test a Simple Circuit