Yes, the SC can be powered on and the contact switch flipped on to use the PEMF and modified contact without engaging the use of a generator to drive the plasma tube and ultrasonic modes.
This is because the PEMF and modified contact ports use a fixed frequency of 100 Hz.
However, you need a generator to drive the other two modes.
If you do not plug in a plasma tube/phanotron, then you can use the ultrasonic output when driven by a generator's input.
However, all 3 of those modes are really designed to be used in conjunction with the plasma output.
For more details, please check the link: