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)

May 16th, 2010

Simple Level Switch Circuit

Circuit Description

The circuit diagram given here is a simple level switch that switches relays between two states according to the fluid level. The main parts of this circuit are three transistors Q1, Q2, Q3 (BC 107) and two relays K1 and K2.

Transistor Q1 is turned ON when fluid level touches the probes since it is connected to positive supply through fluid. The three transistors are interconnected in such a way that the base of Q2 is connected to collector of Q1 and base of Q3 is connected to collector of Q2. Since the interconnection of transistors, when Q1 is ON Q2 will be OFF. The state of relays K1 and K2 are also according to the state of Q1 and Q2 respectively. The contacts of the relays OP1 and OP2 can be used according to application to operate any device such as motor, pumps, solenoids, valves, light, alarm etc.

Circuit Diagram

Simple Level Switch Circuit

Simple Level Switch Circuit

Notes

  • Adjust R1 keeping probes touched in water to obtain the relay K1 ON. Then remove probes from water and see relay K1 goes OFF. During this time the opposite will be happening in K2.
  • One of the main problems in using this circuit is the corrosion of probes. Corrosion free probes will release soon.
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