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.

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 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 ...

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 ...