Power amplifier electronic circuits-tube audio rf amplifiers

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

May 16th, 2010

Direct Coupled Radio Circuit

Circuit Description

Here is the circuit diagram of direct coupled radio. The central and core part of this circuit consists of three transistors Q1 (HEP 641), Q2 (HEP 253) and Q3 (HEP 641) as shown in the circuit diagram. In this circuit, all the three transistors are made to work as audio amplifiers. Among these transistors Q1 has got an additional function. It also acts as a diode detector. The diode detection operation is taking place at the emitter-base junction of Q1 which operates as a PN junction diode. The radio filtering stage in detection process is provided by the base-emitter capacitance of Q1. The consistency in volume and least distortion are obtained by adjusting the potentiometer R1 (47 K).

Circuit Diagram

Direct Coupled Radio Circuit

Direct Coupled Radio Circuit

Notes

  • Use a good quality PCB to assemble this particular circuit.
  • This an excellent direct coupled radio circuit ideal for listening to near by stations.
  • Use a center tapped ferrite antenna coil for L1 that is used AM receivers.
  • Use an appropriate battery for powering this circuit since it can reduce noise in the circuit (A 3V DC battery is used here)

April 28th, 2010

50 Watt Transistor Amplifier Circuit

Circuit Description

The circuit diagram given below is 50 W transistor amplifier. This circuit is a class-B amplifier. In this circuit, seven transistors are used. Out of these transistors, six transistors acts as preamplifiers and the rest one is for driving the speaker. The transistor 2N 3055 is used here to drive the speaker. The 500 ohm pot connected to BC 107 transistor is used for adjusting maximum power level of the amplifier.

In audio applications always use power amplifiers. This circuit is a very rugged and reasonably power amplifier. The capacitors C1 (220 uF) and C2 (100-200 uF) is for controlling low and high frequencies respectively. The circuit can be powered using a 50 V DC power supply with 5A current rating. Up to 60 V can be given to the circuit. This amplifier can produce 60W rms at 50V supply on an 8 Ohm load.

Circuit Diagram

50 Watt Transistor Amplifier Circuit

50 Watt Transistor Amplifier Circuit

Notes

  • The circuit is designed such that most of the components are not critical and can be easily replaced by nearest values
  • This circuit is ideal to assemble from your electronics junk box
  • Volume control can be added to the circuit by connecting a 10 K POT in series to the input of the amplifier.
April 27th, 2010

Cable TV Amplifier Using Transistors

Circuit Description

The circuit diagram of Cable TV amplifier has been published here. This cable TV amplifier circuit consists of two transistors Q1 and Q2 both 2SC1324 as its core part. Type number of these transistors is optional; any medium power NPN RF transistors can be used instead of it. Among these transistors Q1 is meant for amplification and gives a maximum gain of around 20 dB. Transistor Q2 functions as emitter follower. This emitter follower circuit is meant for increasing current gain.

12V DC supply is used for powering this circuit.  It is most applicable for cable TV systems that use coaxial cables of 75 ohms. This particular amplifier has less performance than other high quality cable TV amplifiers available in market since it is a simple elementary circuit.

Circuit Diagram

Cable TV Amplifier Using Transistors

Cable TV Amplifier Using Transistors

Notes

  • Use a Vero board to assemble components for this particular circuit.
  • This amplifier works fine up to 150 MHz in cable TV systems that use 75 ohm coaxial cables.