Using a Transistor Radio as an Amplifier

c) Radio Amplifiers (III)

We hope that by now you have managed to build an audio amplifier by following the instructions in our magazine. But if you haven't had any of the types of radios we have described so far, here's your chance: the radio we are going to describe now is one of the most widespread radios in our country.

It is used mostly for listening to sports matches—you've already guessed it: a transistor radio. Since there are different types and designs, but the principle is generally the same for all of them, we will describe how to modify one.

You will need the following materials: a soldering iron rated up to 25 W, two wires, a banana plug, solder (tinol wire), and, of course, a transistor radio.

You may have a radio with a transformer inside (older models), or a transistor radio with transistors instead of transformers (newer models). The main difference between them is that, during the modification, the second wire is connected to different points.

First, you must open the radio and turn the printed circuit board towards you. Find the volume control potentiometer. Solder your first wire to one of its sides—that is, where the potentiometer makes contact with the printed circuit board and is soldered to it. This applies to both types of radio. Now, for the first type, the one with a transformer: these generally have two transformers, one input and one output, and they amplify the signal from the computer.

For this, you will need a little luck and some probing to find the strongest signal. You can then solder your second wire to the input transformer. How do you tell which transformer is the input and which is the output? The answer is simple: as a rule, two wires almost always come out of the output transformer and go to the speaker, so we can conclude that the other one is the input transformer.

However, this unwritten rule will not always hold, so you may need to experiment a little to identify the input transformer. Now for the second type, the one with transistors. First, find the group of at least three transistors, and then, of course, find where the signal is strongest.

Usually, these transistors are located near the variable capacitor, popularly known as the channel selector. The signal is usually found at the middle leg of one of these transistors, or even at a neighbouring resistor. Now take both wires and solder their free ends to the banana plug.

And with that, you have finished modifying the transistor radio.

We have been together for three issues of ZX REVIJA, in which we have described modifications to the most widespread radios. We will continue in the next issues, and after that we will explain how to turn a gramophone, a stereo system, a cassette player, and even a TV into an amplifier—but more on that later.

Some readers have asked whether, if they turn a radio into an amplifier, they can listen to music. The answer is YES, because that was one of our aims in giving you a RADIO AMPLIFIER.

If you are not familiar with electronics, are afraid to try making a modification yourself, or need advice about the modifications described earlier, write to this address:

Žosić Saša
Podgaj 11
71000 Sarajevo
Tel. (071) 33-049