I learned that two diodes connected in opposition form the circuit equivalent to a transistor. That means if I have two common diodes, I can make a transistor with them. It works.
Not really. The equivalent circuit of the transistor is two diodes in opposition, but only equivalent. What counts in the transistor for it to function as an active device is the way the junctions are arranged in the semiconductor chips. Electrically they behave like diodes, but functionally they go beyond amplifying or controlling signals. Two diodes will not work as a transistor.
Circuit equivalent to an NPN transistor. For the PNP just reverse the two diodes.
