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This tester is primarily meant to test bipolar transistors. It can indicate the type of the transistor as well as identify its base, collector and emitter pins. The circuit is very simple. The direction of current flow from the terminals of the transistor under test (TUT) is indicated by a pair of LEDs (green-red). An npn transistor produces a red-green-red glow, while a pnp transistor produces a green-red-green glow, depending on the test point that connects to the terminal of the transistor. Emitter and collector are differentiated by pressing pushbutton switch S1 that actually increases the supply voltage of the circuit by about 5.1V. At the heart of the circuit is IC CD4069 (IC3), which oscillates and produces pulses required to test a pair of transistor leads for conduction in both the directions. Different combinations are selected by an arrangement of counter CD4040 (IC1) and bilateral switch CD4016 (IC2). Fig. 1 shows the circuit of the bipolar transistor tester. A pair of LEDs...

Mini 3 transistor amplifier is a simple amplifier with 50mW power drawn by 3 transitor. The series of three mini-amplifier transistors can be used for loud speaker 8 ohm load. Source voltage required to activate the mini-amplifier can be drawn from the batteries 9V.Rangkaian 3 transistor amplifier is often used in simple portabe audio devices such as radios or small tape recorder. Mini-transistor amplifier circuit 3 is quite simple as shown in the figure below. Mini-transistor amplifier circuit 3 includes type of amplifier OTL (Output Transformer Less). Mini-transistor amplifier circuit 3 is used for output coupling capacitors. Amplifier circuit is simple and suitable when used for audio amplifier experiment.

 4 Transistor FM Transmitter Circuit Diagram   Build a  4 Transistor FM Transmitter Circuit Diagram. This 4 Transistor FM Transmitter Circuit Diagram provides an FM modulated signal with an output power of around 500mW. The input microphone pre-amp is built around a couple of 2N3904 transistors (Q1/Q2), and audio gain is limited by the 5k preset trim potentiometer.  The oscillator is a colpitt stage, frequency of oscillation governed by the tank circuit made from two 5pF ceramic capacitors and the L2 inductor. The output stage operates as a 'Class D' amplifier, no direct bias is applied but the RF signal developed across the 3.9uH inductor is sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage.