Abstract: A hydromechanical signal transmitter for generating pressure pulses in a drilling fluid to transmit telemetry information of a well-logging operation includes a stator fixed in a cylindrical housing having at least a pair of axially aligned fluid passages, and a disc shaped rotor disposed between the passages, rotatable between a first limit position wherein an opening in the rotor passes drilling fluid flowing through the pair of passages and a second limit position wherein a disc portion of the rotor throttles the flow of the fluid. A revisable d.c. motor drives the rotor from one limit position to the other in response to information signals provided to the motor. Means is provided to stop the rotor at each limit position, including radial stop faces on a drive shaft connecting the motor to the rotor and a stop pin in the housing. A plurality of circumferentially spaced passages and rotor openings may be provided.