 | Radio and Electronics (DED Philippinen, 66 p.) |
 |  | (introduction...) |
|  | 1. INTRODUCTION |
| | (introduction...) |
| | 1.1. A TRIAL TO STATE A DEFINITION OF ELECTRONICS |
| | 1.2. A SHORT HISTORY OF ELECTRONICS |
| | 1.3. CLASSIFICATION OF ELECTRONIC DEVICES |
| | 2. PRINCIPLES OF RADIO COMMUNICATION UNICATION |
| | 2.1. BASICAL IDEAS ABOUT COMMUNICATION |
| | 2.2. DEVELOPMENT OF LONG DISTANCE COMMUNICATION |
| | 2.3. FIDELITY AND DISTORTION |
| | 3. TRANSDUCERS |
| | (introduction...) |
| | 3.1. MICROPHONES |
| | 3.2. LOUDSPEAKERS |
| | 3.3. THE TELEPHON SYSTEM |
| | 3.4. PROBLEM OF FREQUENCY RANGES |
| | 3.5. BANDWIDTH |
| | 4. RADIOWAVES |
| | (introduction...) |
| | 4.1. ORIGIN OF RADIOWAVES |
| | 4.2. PARAMETERS OF ELECTROMAGNETIC WAVES |
| | 4.3. PROPAGATION OF RADIOWAVES |
| | 4.4. SPECTRUM OF RADIOWAVES AND BANDS OF RADIOWAVES |
| | 5. MODULATION OF RADIOWAVES |
| | (introduction...) |
| | 5.1. THE AMPLITUDE MODULATION (AM) |
| | 5.2. FREQUENCY MODULATION (FM) |
| | 5.3. SIDEBANDS |
| | 5.4. TRANSMISSION OF RADIOSIGNALS |
| | 6. RECEPTION OF RADIOSIGNALS (AM - TYPE) |
| | 6.1. AERIAL |
| | 6.2. THE TUNED CIRCUIT |
| | 6.3. INCIDENTAL REMARK ON BLOCK DIAGRAMS |
| | 6.4. DETECTOR OR DEMODULATOR |
| | 6.5. POWER SUPPLY |
| | 6.6. AMPLIFIER |
| | 6.7. SUPERHET RECEIVER (the SUPER) |
| | 6.8 INCIDENTAL REMARK ON MIXING FREQUENCIES |
| | 6.9. CONSTRUCTION OF A SUPERHETRADIO |
| | 7. COMPONENTS OF MODERN RADIO RECEIVERS |
| | 7.1.1. HANDLING OF ELECTRONIC COMPONENTS |
| | 7.1.2. HANDLING OF PRINTED CIRCUITS |
| | 7.1.3. DIFFERENTIATION OF COMPONENTS |
| | 8. PASSIVE COMPONENTS |
| | 8.1. RESISTORS ELECTRICAL CHARACTERISTICS |
| | 8.2. CAPACITORS |
| | 8.3. INDUCTORS |
| | 8.4. COMBINATION OF PASSIVE COMPONENTS |
| | 8.4.1. SERIES CONNECTION OF R AND C, OR R AND L |
| | 8.4.2. COMBINATION OF L AND C, RESONANT (TUNED) CIRCUITS |
| | 8.4.3. TUNED CIRCUIT CONNECTED TO AN AC-VOLTAGE |
| | (introduction...) |
| | 8.4.4.1. QUALITY OF TUNED CIRCUITS |
| | 8.4.4.2. BANDWIDTH |
| | 9. ACTIVE COMPONENTS -1- DIODES |
| | 9.1. CHARACTERISTICS OF SEMICONDUCTORS |
| | 9.2. THE PN-JUNCTION OR DIODE |
| | (introduction...) |
| | 9.2.1. PN-JUNCTION CONNECTED TO VOLTAGE |
| | 9.2.2. CHARACTERISTICS OF A PN-JUNCTION OR DIODE |
| | 9.2.3. ZENERDIODE |
| | 10. BLOCKS OF RADIOS / -1- / POWER SUPPLIES |
| | 10.1. GENERAL CONSIDERATIONS |
| | 10.2. TRANSFORMER |
| | 10.3. THE RECTIFIERS. |
| | 10.4. SMOOTHING AND FILTER CIRCUITS |
| | 10.4.1. THE RESERVOIR CAPACITOR |
| | 10.4.2. FILTER CIRCUITS |
| | 10.5. STABILIZATION |
| | 10.5.1. GENERAL REMARKS |
| | 10.5.1.1. LOAD VARIATIONS |
| | 10.5.1.2. INTERNAL RESISTANCE OF VOLTAGESOURCES |
| | 10.5.1.3. PROBLEMS CAUSED BY THE SMOOTHING CIRCUIT |
| | 10.5.5. METHODS OF STABILIZATION |
| | (introduction...) |
| | 10.5.5.1. PARALLEL-STABILIZATION |
| | 10.5.2.2. SERIES STABILIZATION |
| | 11. ACTIVE COMPONENTS -2- / TRANSISTORS |
| | 11.1. CONSTRUCTION OF A TRANSISTOR |
| | 11.2. CHARACTERISTICS OF TRANSISTORS |
| | (introduction...) |
| | 11.2.1 HANDLING OF CHARACTERISTICS OF TRANSISTORS |
| | 11.2.1.1. CONSTRUCTION OF THE STATIC-MUTUAL-CHARACTERISTICS |
| | 11.2.1.2. CONSTRUCTION OF THE DYNAMIC MUTUAL CHARACTERISTICS |
| | 11.2.1.3. CONSTRUCTION OF THE MAXIMUM-POWER-LINE |
| | 12. AMPLIFIERS |
| | (introduction...) |
| | 12.1. STRUCTURE OF A CLASS A AMPLIFIER |
| | 12.2. FUNCTION OF A SIMPLE CLASS A AMPLIFIER |
| | 12.3. ADVANCED CLASS A AMPLIFIER |
| | 12.4. STABILIZATION OF THE QUIESCENT VOLTAGE |
| | 13. CLASS B AMPLIFIERS |
| | 13.1. LIMITS OF CLASS A AMPLIFIERS |
| | 13.2. CLASS B AMPLIFIERS WITH TRANSFORMERS |
| | 13.3. CLASS B AMPLIFIERS WITHOUT TRANSFORMERS |
| | 13.4. POWER AMPLIFIER WITH COMPLIMENTARY TRANSISTORS. |
| | 14. DETECTOR OR DEMODULATOR |
| | 15. AGC-AUTOMATIC GAIN CONTROL |
| | 16. IF-AMPLIFIERS |
| | 17. FEEDBACK |
| | 18. OSCILLATORS |
| | 19. FREQUENCY CHANGERS MIXERSTAGE |
| | 20. DECOUPLING CIRCUITS |
| | 21. MATCHING OF AMPLIFIERSTAGES |
| | 22. COUPLING OF AMPLIFIERSTAGES |
| | 23. RADIO SERVICING |
| | 23.1. IMPORTANCE AND SUBJECT OF FAULT FINDING |
| | 23.2. FAULTS AND FAULT FINDING |
| | 23.3. FAULT FINDING METHODS |
| | 24. THE USE OF THE OSCILLOSCOPE |
13.1. LIMITS OF CLASS A AMPLIFIERS
In very cheap and small transistorradios we find sometimes - as an exception - class A amplifier even for the power stage, but operating only an earphone or a very tiny loudspeaker. The reason why is easy to see if we have a closer look to the quiescent point.
fig. 153
If you have a short look back to fig. 144a you will easily see, that in this case in a class A amplifier the output-voltage must be half of the supply voltage. The collector-current is therefore half of the maximum current and this means: AT QUIESCENCE (NO INPUT SIGNAL AND NO OUTPUT SIGNAL) THE POWER CONSUMPTION OF A CLASS A AMPLIFIER IS ALREADY 25 % OF THE MAXIMUM POWER CONSUMPTION OF THIS STAGE.
This makes clear: for high amplification of considerable power another kind of amplifier is necessary otherwise the energy losses are too much.
The next amplifier class which we will come to know now is called class B amplifier and it is designed for power-amplification.
A difference between class A and class B amplifiers easily to be realized is:
- Class A amplifiers amplify with a single transistor a whole sinewave of the input signal.
- Class B need at least two transistors to do the same.
GENERALLY:
If we want to avoid the losses - caused in a class A amplifier at quiescence - we have to shift the quiescence working point to lower powers.
This can be achieved by reducing the base-current to about “0”.
But if the base-current is kept “0” at quiescence at the output of a COMMON-EMITTER-CONNECTION (as we call the transistor circuit used up to here) can only be produced half of a sine-wave as shown in fig. 154.
fig. 154
So we have to use two transistors in order to amplify both parts of the sinewave and to find a way how to “couple” both parts together again.
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