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I ran across this IBM computer aided design and simulation software demonstration from the 1960's in the video The Incredible Machine (1968)

The gain vs frequency plot shows what looks like the characteristics of a low-pass filter, but is that what's shown in the diagram? Could the 3-terminal device at the bottom be a transistor?

The GIF was made at about 02:44 in the video.

The Incredible Machine (1968) circuit simulation

The Incredible Machine (1968) circuit simulation

The Incredible Machine (1968) circuit simulation

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    \$\begingroup\$ At one point their simulation doesn't work/ flags an error and one says to the other we forgot to put in the input impedance of the amplifier. So it might be an amplifier equivalent circuit. The three terminal symbol I have no idea, looks vaguely like a variable resistor \$\endgroup\$ – IC_Eng Apr 16 at 14:52
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There isn't much detail in the movie, but from how they talk about it, I suspect that it's just an abstract model of an amplifier — a voltage-controlled voltage source, with parameters for input and output impedance.

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The colleague on the right suggests that the 3 terminal device might fit best in the lower right corner. This is the CFA or current feedback amplifier that permits full duplex audio on a single pair of wires.

The gain must be critically controlled to cover line loss without gain>1 and includes conjugate line filter equalization.

The full duplex audio is separated from the differential voltage from one end source and the differential current source of the other end-source.

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