Two Transistor Radio
This is a two Transistor receiver which has sufficient gain and selectivity to drive a Speaker to adequate volume. As with all simple radios like this, use a good Antenna and Ground system. Try the Antenna on 10 pF and then 100 pF. Use the connection that gives the best results.
The detector stage uses a germanium (Ge) Diode and 22K detector load Resistor. Try operation without the 22K Resistor. Replace it with an open circuit by simply lifting the lead from them.
Results are __________________ (worse, improved) for weak stations and ___________ (worse, improved) for strong stations.
The first 2SA(1) stage is a class A audio amplifier which uses universal bias. The bias arrangement always uses a voltage divider of two Resistors to obtain base-bias voltage, and then an emitter swamping Resistor.
A 470uF Capacitor is used to eliminate the AC feedback from the 470 ohm Resistor while allowing it to provide DC feedback to obtain good stability for the stage.
The 100 ohm Resistor and 100uF Capacitor form a decoupling filter for the DC bias, fed to the first stage.
This circuit eliminates the tendency for oscillations, due to Battery impedance, that might otherwise allow these high gain stages to oscillate (due to feedback from the AC voltage developed across this impedance).