A receptacle for receiving a plug connector of a high-voltage cable for a microfocus X-ray tube with a cathode, which has a metal filament and grid. The receptacle has a ceramic insulator with three contiguous cavities. The first cavity near the filament includes electrical contacts for the filament and the grid. The second cavity includes spring contacts for supplying current to the filament and a center pin for supplying voltage to the grid. The third cavity receives the plug connector. The insulator has a removable grid cap which is conductively connected to the grid of the cathode. The first and second cavities are surrounded in the radial direction by the grid cap, An air gap extends radially between grid cap and ceramic body. At the end of the grid cap remote from the filament is a circumferential groove in the axial direction between the grid cap and the ceramic insulator.