In my case it was around 1975ish. There was no digital circuitry in signal paths then.

If you are asking how the thread pitch motor controller was working I have no in depth knowledge but it would likely be an analog envelope detector. (simple RC filter/integrator would suffice) That would be rectified to make a DC control voltage and the control voltage would be used to modulate the power to the motor in an inverse fashion. ( more audio signal -> less power )

No digits would be harmed in the process. :)

The RIAA equalization curve for recording and playback, was typically implemented with only resistors and capacitors. No DSP required.

I know I know. It's so hard to believe you can manipulate signals without a processor. ;-)