Beginner radio amateur. Theory. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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Congratulations! You've built your own amplifier! But you still don't understand how it works. I deviate from the general training scheme and tell the theory after practice. Let's take a look at the diagram again:
First, as promised, I will talk about the transistor. At first, use transistors of the MP39 - MP41 types, they are easier to solder and they have a pnp structure. When a positive voltage is applied to the base of an npn type transistor, it opens, i.e., the resistance between the emitter and the collector decreases, and when a negative voltage is applied, on the contrary, it closes and the stronger the current, the stronger it opens or closes. For pnp transistors, the opposite is true. In our amplifier, this property of the transistor is very well revealed.
Capacitor C1 is supplied so that when we connect a microphone or tape recorder head to the amplifier input, direct current does not get to the base of the transistor. After all, the direct current of the battery cannot pass through capacitors, but the alternating current from a microphone or head can easily! And this same alternating current enters the base of the transistor, and it either opens or closes it in time with what they say into the microphone. And a relatively large battery current flows through the collector and emitter of the transistor (and headphones), and it also changes in time with the vibrations of the microphone. How! There was a current of hundredths of a volt from the microphone, but it became a few volts from the battery. Therefore, the amplifier is called an amplifier.
Question: "Why resistor R1?".
Response: "A small turn-off bias voltage is applied through it to the base of the transistor for stable operation of the transistor."
Question: "Why capacitor C1?" Response: "I don't know, and without it everything works fine, but the books say that it is blocking."
Before amplification:
After amplification:
Look at these pictures, maybe you see this for the first time, these are sinusoids. From them, you can determine the frequency of current oscillations, that is, how many times per second the current will change its polarity.
T - period.
For example, 1 mm is equal to 0,0001 seconds, let's measure the distance from one vertex to another, let it be 50 mm, multiply 50*0,0001=0,005 now calculate the frequency using the formula:
f=1/T
where f is the frequency, we get 1/0,005=200 (Hertz). In short - 200 Hz.
Publication: cxem.net
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