Power amplifier electronic circuits-tube audio rf amplifiers

Electronic Amplifier Circuits-Power amplifier, audio amplifier designs and circuits

April 25th, 2010

Simple 250 mW Audio Amplifier

Circuit Description

The circuit diagram given below shows 250 mW audio amplifier. This circuit contains three transistors Q1 (BC547), Q2 (BC327), Q3 (BC337) as central components. Transistor Q1 in this circuit acts as preamplifier where as Q2 and Q3 are output pairs. Transistors Q2 and Q3 are complementary transistors. Decoupling of DC from audio source is done by the capacitor C1 (10 uF). Resistor R2 (82K) is used in this circuit to provide better stability for the amplifier. Variable resistor POT R5 (10K) is used as volume control element.

The circuit is powered using a 9V DC supply. The value of impedance of speaker K1 can be 8 ohm. In order to get the optimum output from the circuit, decouple input and output grounds properly.

Circuit diagram

Simple 250 mWAudio Amplifier

Simple 250 mWAudio Amplifier


  • Use a Vero board to assemble components for this circuit.
  • This type of amplifiers finds applications in small radio sets and in high power amplifiers as preamplifier.

August 22nd, 2009

Simple Power Megaphone Circuit

About The Circuit


Here isthe circuit diagram of a simple power megaphone circuit. All you have to look out for is whether you get the perfect power and speaker matching. For that the transistors Q1 and Q2 (HEP 230) are connected in parallel. An input voltage supply of 12 Volts is required. It can be either given from a battery supply or a DC power supply. A carbon type michrophone is more than enough for the circuit to work. It is the same component that is used in our ordinary telephone sets. A Push-to-talk (PTT) switch can be easily setup if we use an ordinary carbon type michrophone.

Any type of power transisitors can be used for this circuit. You have to only look out that the transistors used are kept on heat sinks. The volume control can be adjusted wiith the help of the POT R1, through which you will get max. volume with min. distortion. Take a look at the circuit diagram given below.


Circuit Description



August 21st, 2009

Simple Amplifier circuit for Headphones

About The Circuit

Though the headphones that are present in the market today are good enough, the music player may not be able to provide enough power to drive the headphone. The only way to make them produce a clear and gud sound is to amplify them. For this, a very simple circuit is enough consisting of three amplifiers. The circuit only needs a 3 Volts battery and needs to be made on a good quality Printed Circuit Board.
The transistors used for this circuit are BC 239 BC 337 and BC 327. Out of these Q1 (BC 239) acts as the pre-amplifier, while transistors Q2 (BC 337) and Q3 (BC 327) act as the driver circuit for the speaker. The performance of the circuit is increased by feeding back the emitter voltage of Q1 the base of Q1 itself through the resistance R3. You must also note down that the capacitors have a rating of 10 Volts. After the circuit is made all you have to do is ON/OFF the switch S1.


Circuit Schematic