Build Your Own Transistor Radios

Chapter 6Transistor Reflex Radios

This chapter introduces a method of using a form of signal recirculation to reduce the number of active components for amplification in radios. Unlike the tunable radio-frequency (TRF) radio circuits shown in Chapter 5, where each amplification stage amplified only one type of signal (e.g., an RF signal), reflex radio circuits allow a single transistor stage to amplify both radio-frequency (RF) and audio-frequency (AF) signals.

Motivation Behind Amplifying Both Radio-Frequency and Audio-Frequency Signals

When the first transistor radios were designed and sold commercially in the mid-1950s (e.g., the four-transistor radio Regency TR-1 in 1955), transistors were very expensive. In the mid-twentieth century, audio ...