Mfa 919d2pr panel mounted bi directional variable speed regulator mfa 919d2pr a panel mounted speed regulator that features a constantly variable bi directional output these units are designed to be used with miniature and sub miniature motors and are suitable for a range of applications the motor can be powered from a dc source either battery or transformer recitifier transformer rectifier must have a non digital output pwm circuitry is employed which varies the output pulse width to