Understanding how the Motown, Altec9062A attenuation part of Equalizer operates with possible schematic, on patent US3624298, assignee LTV Ling Altec, Inc. Anaheim, Calif.

At your risk. The patent explains in detail 1/3 octave band attenuation equalizers, ie an EQ with greater resolution, but the principle and components used seem to be the same. A very recent light giving paper is Graphic Equalizers Based on Limited Action Networks, by Kurt James Werner. Inside the paper are actual measurments, equations given too.