Please see xwhatsit’s solenoid driver documentation for additional details: https://static.wongcornall.com/ibm-capsense-usb/
My new solenoids are specced 6V 0.15A 40 ohms DC resistance.
Quoting what someone shared with me:
The solenoid driver “is designed to drive solenoids at 9V with coil resistances down to about
25-30 ohms. The original solenoids fitted to the Beamspring keyboards are
around 33 ohms, which translates to just under 300mA. The solenoid driver is
current limited, so lower coils with lower resistance will still work, but may not
be as “snappy”.”
My original IBM 3278 beam spring solenoid is 41 ohms (translates to 220 ma at 9v). Other beam spring keyboards used other solenoids.