Economical Transistor Radio

The schematic diagram shows an audio stage with a common-collector circuit. This does not damp the tuned circuit, but instead actually increases its response. This yields good sensitivity and selectivity. Due to the low supply voltage, the subsequent audio amplifier needs three transistor stages. The volume is adjusted using the potentiometer. This radio works well using an internal ferrite rod (around 1 cm diameter and 10 cm long) with a winding of around 50 turns of enameled copper wire. With a two-meter external wire aerial, you can receive even more stations. This radio is not only economical in terms of components, it also needs very little ‘juice’: since the current consumption is only 10mA, an alkaline AA cell will easily last for around 200 hours of operation.


The specifications, very briefly stated, are:

• medium-wave receiver with ferrite aerial
• optional supplementary aerial
• power supply 1.5 V/10 mA
• 4 transistors
• loudspeaker output

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One Transistor Radio

Here is a simple circuit for a one transistor Audion type radio powered by a 1.5 V battery. It employs a set of standard low-impedance headphones with the headphone socket wired so that the two sides are connected in series thus giving an impedance of 64 Ω. The supply to the circuit also passes through the headphones so that unplugging the headphones turns off the supply. Using an Audion configuration means that the single transistor performs both demodulation and amplification of the signal.

The sensitivity of this receiver is such that a 2 m length of wire is all that is needed as an antenna. The tap on the antenna coil is at 1/5th of the total winding on the ferrite rod. For details of the antenna coil see the article Diode Radio for Low Impedance Headphones. This circuit is suitable for reception of all AM transmissions from long-wave through to shortwave.

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