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 plenty of tube amplifiers now being manufactured, with a popular choice being headphone amplifiers that use a tube as a gain stage followed by an op-amp as a buffer with a low impedance ...

Linear Tech is aiming at high-impedance sensor transimpedance amplifiers with an op-amp that requires only 3fA of bias current (typical at 25°C) while offering 500MHz gain bandwidth product ... stages ...