Old School Propulsion Question

This is a question for the old hats that worked in the car shops.
DC Propulsion cars were (for the most part) either GE or Westinghouse.
DC traction motors with series-parallel switching and a cam driven controller & resistor grids.

Specifically GEs system. They called the 1960's onward systems SCM-##. SCM meaning Static Cam Magnetic. I never quite knew what was meant by 'static' but, CAM to mean the camshaft driven switching gear, and magnetic, the magnetic contactors.
LIRR/MNR M1/M3s have the same family of system.

Read recently that some model of cars (Maybe R30) had a newer solid state SCM system, as opposed to GE's earlier MCM system.

Here's my question, assuming MCM is M(something)-CAM-MAGNETIC.

What was the 'M' CAM system, if SCM is solid state? Did it use vacuum tubes? Something else?

SCM stands for Simplified Cam Magnetic. The basic idea is similar to earlier GE MCM (Motorized Cam Magnetic) and "PC" (Pneumatic Cam) controls, with the cam moved by a single motor, instead of paired electric motors or pneumatic cylinders. SCM was also used in Chicago on 2000, 2200 and 2400 series cars built between 1964 and 1978.

SCM uses solid-state circuits to control cam advancement and to measure current. PC and MCM use parts similar to, but larger than, old-fashioned automotive voltage regulators.

Allouette wrote: ↑Mon Dec 12, 2022 7:27 pm SCM stands for Simplified Cam Magnetic. The basic idea is similar to earlier GE MCM (Motorized Cam Magnetic) and "PC" (Pneumatic Cam) controls, with the cam moved by a single motor, instead of paired electric motors or pneumatic cylinders. SCM was also used in Chicago on 2000, 2200 and 2400 series cars built between 1964 and 1978.

SCM uses solid-state circuits to control cam advancement and to measure current. PC and MCM use parts similar to, but larger than, old-fashioned automotive voltage regulators.

Thank you, I would have thought vacuum tubes wouldn't be too good for transit cars. The old style voltage/current regulator setup makes more sense. I can only imagine how finicky they were, especially in that environment.

M1/M3 use the same SCM system, but the manuals call it Static Cam,,,

Thank you.