KT315 is a legendary domestic transistor, copies of which are present in large quantities in every radio amateur. Not surprising - after all, this is the very first mass-produced silicon transistor; you can find it in almost any Soviet device. By the beginning of the 90s, more than 7 billion of them were manufactured. By modern standards, the KT315 is far from an ideal transistor in terms of its parameters, because new, cheaper and more advanced semiconductor devices have been invented and have been produced for a long time. But, nevertheless, sometimes you want to take a handful of old transistors out of the back drawer and assemble something simple with them, for example, an amplifier.
Scheme
The circuit is special in that it does not contain any other active elements except KT315 transistors. This circuit will be an excellent choice not only for antique lovers, but also for those who do not have the opportunity to get other transistors. Resistor values are not very critical and can vary within 20-30%, the same with capacitors. It is advisable to select transistors for this circuit with a high gain, in this case the maximum volume of the amplifier will increase.In this case, it is necessary to comply with the condition - both transistors of the output stage must have the same letter index. The circuit starts working with a voltage of 5 volts, the most optimal power supply is 9 volts. The current consumption is approximately 20 mA and is almost independent of the volume level. It should also be taken into account that to reproduce a stereo signal, the circuit must be repeated twice.
Amplifier assembly
The circuit is assembled on a printed circuit board measuring 50x40 mm, which already contains both channels. First of all, using laser-iron technology we produce the board itself. Below are some photos of the process.
Once the board is ready, you can start soldering the parts. First of all, resistors are installed on the board, then capacitors with transistors. The terminals of KT315 transistors, unlike the terminals of modern parts, are thin flat strips that come off very easily from the body, so you should not apply too much force to them.
After installing the parts on the board, you need to check the adjacent tracks for short circuits and check that the transistors are installed correctly - after all, they can easily be soldered on the wrong side. The base terminal of the KT315 is on the right when looking at the front side of the transistor. Now all that remains is to connect the board with the speakers and sound source using wires, apply power and the amplifier is ready.
First launch and tests
The amplifier can work with speakers with a resistance of 4-8 Ohms, and you can also connect headphones to its output, which do not have enough power from the standard signal source. The signal source can be, for example, a telephone, player or computer.Before connecting one of the supply wires for the first time, you need to turn on the milliammeter and measure the current consumed; it should not exceed 100 mA in total for both channels. If it exceeds, then it is necessary to reduce the supply voltage. Due to its low consumption, this amplifier can even be powered from the crown. The power of the resulting amplifier is approximately 0.1 watt - not much, but quite enough for quiet listening to music indoors. Happy building!
