A commercial 50 mm microfocus cathode ray tube has been redesigned to incorporate a carbon-fibre field-emission electron source that can be thermally processed in situ to avoid 'tip explosion'. With the aid of an external optically controlled feedback system, it has been possible to eliminate the characteristic low frequency (<or=10 Hz) fluctuations in the emission current associated with this type of source, and thereby obtain a high-definition and stable display image at pressures <or=10^-6 Pa.