I needed to make an amplitude modulator as part of a signal generator design. I took the approach of using an RCA type CA3004 as a variable transconductance amplifier. It worked very nicely. Figure 1 ...

Simple long-tailed pairs had a long history prior to the advent of integrated circuits, starting in the 1930s with tube circuits and being recreated with transistors as those devices were invented.

If we replace the potentiometer VR1 with an AC signal plus DC bias signal in any of the previous Figures 3 to 17, the voltage controlled attenuators can become an amplitude modulator circuit instead.