I have had a look at an F4B flight manual and an FG 1 manual on the web - its surprising what's out there. The F4B manual says the variable ramp starts to move at a TOAT of +45 deg C and is fully extended to an angle of 14 degrees at a TOAT of +146 deg C. Assuming a static OAT of -40 deg C, typical of 40,000 ft, the ramps will start to move at Mach 1.4.
The FG Mk 1 flight manual does not quote the schedule but says the variable ramp moves 16 degrees so there must be some differences between J79 and Spey engined aircraft. There would be no software involved back in the 1960s, I am sure it would all have been analogue electronics.
For those of you wondering about the purpose of the ramps, their role in life is to create a pair of oblique shockwaves across the front of the intake, one originating at the front of the fixed ramp and the second at the front of the variable ramp. A final normal shockwave originating at the back edge of the variable ramp slows the air down to subsonic speed. By progressively reducing the speed of the air in a series of steps, rather than one big jump through a normal shock, the pressure recovery of the intake, and the overall system efficiency is maximised. Of course its actually the aircraft that's moving supersonically, not the air, but its all relative, as Albert Einstein said (I think)
Walbut