Perhaps there is no more or less complex electronic device manufactured in the USSR during the seventies, eighties and nineties, in the circuit of which the KT315 transistor would not be used. He has not lost popularity to this day.
There are several reasons for this prevalence of this semiconductor device . First of all, its quality. Thanks to the belt-conveyor method, which was revolutionary in the late sixties, production costs were reduced to a minimum with very good technical indicators. Hence the second advantage - an affordable price that allows the use of KT315 transistors in mass consumer and industrial electronics, as well as used for amateur radio devices.
The letter K is used in the designation, meaning "silicon", like most semiconductor devices manufactured since then. The number "3" means that the KT315 transistor belongs to the group of broadband devices of small power.
The plastic case did not imply high power, but was cheap.
The KT315 transistor was produced in two versions, flat (orange or yellow) and cylindrical (black).
In order to make it more convenient to determine how to mount it, a bevel is made on its “front” side in the flat version, the collector in the middle, the base on the left, and the collector on the right.
The black transistor had a flat cut; if the transistor was placed toward it, the emitter was on the right, the collector on the left, and the base in the middle.
The marking consisted of a letter, depending on the permissible supply voltage, from 15 to 60 volts. The power also depends on the letter, it can reach 150 mW, and this with microscopic sizes at that time - width - seven, height - six, and thickness - less than three millimeters.
The KT315 transistor is a high-frequency one, this explains the breadth of its application. A bandwidth of up to 250 MHz ensures its stable operation in radio circuits of receivers and transmitters, as well as sound wave amplifiers.
Conductivity - reverse, npn. For a pair using a push-pull amplification circuit, a KT361 was created with direct conductivity. Outwardly, these “twin brothers” practically do not differ, only the presence of two black marks indicates pnp conductivity. Another marking option, the letter is located exactly in the middle of the case, and not on the edge.
With all its advantages, the KT315 transistor also has a drawback. Its findings are flat, thin, and very easily broken off, so installation should be done very carefully. However, even after ruining the part, many radio enthusiasts managed to fix it by sawing up the case a little and “dipping” the delay, although this is difficult, and there was no special sense.
The case is so peculiar that it accurately indicates the Soviet origin of the KT315. You can find an analogue for it, for example, BC546V or 2N9014 - from imports, KT503, KT342 or KT3102 - from our transistors, but the record low cost makes such tricks senseless.
Billions of KT315 have been released, and although today there are microcircuits in which tens and hundreds of such semiconductor devices are built in, sometimes they are still used to assemble simple auxiliary circuits.