An apparatus for operating a hydrodynamic torque converter and a corresponding converter-bypass clutch of a transmission, having a solenoid valve communicating with a variable pressure control valve. The respective valve stem assembly thereof having surfaces which react to an application of hydraulic pressure. Each valve being controlled by a pilot pressure countering a spring arrangement. A spent fluid flow side of the torque converter communicates with a spent fluid flow aperture of the solenoid valve. The valve stem assembly related, to the solenoid valve is blocked by a supply aperture of the solenoid valve and is in operational connection with an auxiliary pressure control valve. A supply aperture of the variable pressure controller valve is connected with an operational pressure aperture of the pressure control valve, which, can be connected with a piston space of the converter-bypass clutch, which pressurized hydraulic fluid can be applied.