Notes
The part number is given as KEH10903 here:
http://systemjsynthesizers.co.uk/Roland-TR-808-Start/Stop-Switch-Original-Alps (STRONIC list this as MC-4, and finally I understand what MC-4 means — the Roland MC-4 used these switches).
This is not strictly linear: it is closer to progressive rate. The spring is stronger than the dome (which is fairly flat), so as the slider is pressed, the dome collapses first, in a linear manner. The spring does also appear to compress somewhat at the same time, extending the pretravel.
Once the dome is fully depressed, the return spring provides all the force, and being stiffer than the dome, the overtravel period is stiffer than the pretravel period, but still linear.
