The PE 1642, PE 1644, PE 1646 and PE 1648 are 400 W stabilized d.c. power supplies, which provide maximum output when convection cooling is used and the ambient temperature is lower than 40°C. The power supplies are intended for 19-inch rack-mounting but can be adapted for use as free-standing versions. Optimum efficiency is obtained by means of a thyristor pre-regulator and the transistor series-regulator gives good control and stability with minimum ripple. The output voltage, current and the overvoltage protection can be continuously adjusted. Several instruments may be series or parallel connected. Other facilities include : remote sensing, "master-slave" series or parallel operation, remote ON-OFF, voltage and current programming, crowbar protection.