3 Transistor Audio Amp (50 milliWatt)

Here is a little audio amplifier similar to what you might find in a small transistor radio. The input stage is biased so that the supply voltage is divided equally across the two complimentary output transistors which are slightly biased in conduction by the diodes between the bases. A 3.3 ohm resistor is used in series with the emitters of the output transistors to stabilize the bias current so it doesn't change much with temperature or with different transistors and diodes. As the bias current increases, the voltage between the emitter and base decreases, thus reducing the conduction. Input impedance is about 500 ohms and voltage gain is about 5 with an 8 ohm speaker attached. The voltage swing on the speaker is about 2 volts without distorting and power output is in the 50 milliwatt range. A higher supply voltage and the addition of heat sinks to the output transistors would provide more power. Circuit draws about 30 milliamps from a 9 volt supply.

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4 Transistors Tracking Transmitter

DESCRIPTION:

This tracker works with your regular AM/FM radio or car stereo. Car stereo would be best because it is designed to perform optimum in all conditions.

Real distance is unknown at this time because I never measured it accurately but guess about 300 feet (100 meters). The reception of the signal also depends on the surroundings like tall buildings etc. Most likely the best performance is optained with line-of-sight.

If you can somehow use a longer antenna and beef up the supply voltage to 12V, the performance will be a lot better, just make sure the electrolytic capacitors have the correct working voltage (25V) 1/8" (" = inch) is approximately 3.5mm. 22 ga (USA gauge) is approximately 1.5mm. Antenna: 10 - 12" is approximately 25 to 30cm. A "Non-conductive" core means: wooden dowel, plastic, paper, etc.

47K means 47,000 ohms. The 'K' stands for '1000'. C2/C5: .001uF is the same as 0.001uF or 10nF (nanoFarad). A 'trimmer' capacitor (C3) is an adjustable air capacitor (available everywhere).

The 'ground' symbol shown at the end of Q2's emitter (e) is the negative side of the battery supply.

This circuit belonged to the collection of Art Swan's "Circuit Land".