Regency TR1: First mass produced transistor radio, 1954 A silicon transistor may be used if the base-bias resistor is changed according to the table.Ĭrystal radio with one transistor audio amplifier, base-biasįor more crystal radio circuits, simple one-transistor radios, and more advanced low transistor count radios. A schottky diode may be substituted for the germanium diode. The original circuit used a germanium diode and transistor. The circuit in the figure below adds an audio amplifier to the crystal detector for greater headphone volume. However, the low impedance earbuds commonly used with portable audio equipment may be substituted when paired with a suitable audio transformer. The 2000Ω headphones are no longer a widely available item. No-bias-resistor causes operation as a detector Reverse battery polarity for NPN silicon devices. However, a silicon device should still work. This is probably more sensitive, due to the lower 0.2V VBE, compared with silicon. Note the transistor is a germanium PNP device. This more powerful circuit can readily drive 2000Ω magnetic headphones. An advantage of a transistor detector is amplification in addition to detection. Since the transistor is not biased in the linear region (no base bias resistor), it only conducts for positive half cycles of RF input, detecting the audio modulation. The circuit in the figure below produces a stronger output than the crystal detector. The ceramic earphone is desirable for all but the strongest radio signals. While 2000Ω magnetic headphones are shown above, a ceramic earphone, sometimes called a crystal earphone, is more sensitive. A germanium diode, which has a lower forward voltage drop, provides greater sensitivity than a silicon diode. Note that no power supply is required for a crystal radio. C2 is sized to filter the radio frequencies from the RF envelope (c), passing audio frequencies (d) to the headset. The diode passes the positive half cycles of the RF, removing the negative half cycles (c). The variable capacitor C1 allows for tuning to the various signals. Its purpose is to select one out of many available radio signals. The combination of C1 and L1 comprises a resonant circuit, referred to as a tank circuit. The antenna absorbs transmitted radio signals (b) which flow to ground via the other components. (d) Demodulated audio to headphones.Īn antenna ground system, tank circuit, peak detector, and headphones are the main components of a crystal radio seen in figure (a). (c) Rectified RF at diode cathode, without C2 filter capacitor.
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