These are burned in for 24 hours, factory matched at real world voltages and then the test results are labelled on each tube box. Being new tubes, these come with the factory 90 day warranty.
They are matched by the factory at 400V plate, 225V screen and -19.1V bias.
The KT88 Mullard is an exact copy of the KT88 valves that were manufactured by Marconi-Osram for Marshall in the late 1960s and 1970s. Excellent replacement output valve for the Marshall Major to retain the original sound or for any amp where you want a warm, lush sound.
Photos are representative, actual matched specs will be different than those in the photo.