Looking at the circuit diagram it follows the classic op-amp with a long-tailed pair of NPN transistors driving a PNP gain stage and finally a complimentary emitter follower as an output buffer.

The diagram illustrates the basic design of an NPN junction transistor ... which is how a transistor functions as an amplifier. It’s similar to the way you control the flow of water with ...

There are equivalent P-channel devices, just as there are PNP and NPN bipolar ... than a current amplifier, its input impedance is many orders higher than that of a bipolar transistor, and thus ...

The first transistor was about half an inch high ... This contraption was the very first semiconductor amplifier, because when a bit of current came through one of the gold contacts, another ...