Power amplifier electronic circuits-tube audio rf amplifiers

About The Circuit
Given below is a 100 Watts sub-woofer amplifier that has been designed only with the use of transistors. There are mainly seven transistors, in which two of them are used in the pre-amplifier stage and four of them in the output stage.
The greatest advantage of this type of a circuit is that there are no IC’s used and so is easy to assemble on a PCB. This circuit is designed to produce 100 Watts output and an input power of +35V/-35V, 5A dual supply is to be used. The size of the sub-woofer depends on the outpu and a normal specification of 12 inch is required. It must be noted that the transistors Q4, Q5, Q6 and Q7 are fitted along with heat sinks. The electrolytic capacitors used here should have a rating of 100 Volts.

Circuit Schematic

About The Circuit

A 2 transistor tone controller circuit is illustrated below. This simple circuit is made with the help of Baxndal tone control design. A 12 Volt DC power os required for the circuit. Also note that the connection for the input and output is given in respect to the ground. Two POT’s are used. Out of these POT R5 is to bring adjustments to the bass and POT R8 is to bring adjustments to the treble. Sufficient current gain and input impedance must be provided by the circuit. For this reason, the transistor Q1 is placed as an emitter follower. Voltage amplification of the signal is provided by the second transistor. Tone is controlled by the resistor and capacitor network connected between emitter of Q1 and base of Q2. Variation of the values of these resistors and capacitors change the audio response of the system. On the frequency ranges of 10KHz to 60Hz, a maximum attenuation and boost of 10decibel is obtained. All electrolytic capacitors should have a rating of atleast 12 Volts.

Circuit Schematic

About The Circuit

A circuit diagram of a simple stereo line driver circuit is given below. BC 109c transistors are used for driving each channel by wiring them as emitter followers. Apart from the transistors, only a few passive components are wired. The emitter followers are very ideal for driving long cables. They have a voltage gain of and also a high current gain and low output impedance, which makes tem ideal for driving loud speakers.

The circuit should be made on a PCB with a 12 Volt power from a battery or a DC power supply. It must also be noted that the line driver circuit is placed near  to the audio source. At the listening end, a power amplifier is required as the emitter follower has only unity voltage gain.

Circuit Schematic