The KT41 was M-OV's version of a second-generation output valve, with the 1930s standard 4.0 V heater, it replaced Type N41. The KT type number proclaims that it is a beam tetrode, not a pentode - however, the construction is clearly a pentode. The KT41 was unexciting (though quite adequate) in terms of power output but gave better quality sound than most of its pentode competitors and was a successful valve.
Its manufacturing life was truncated when M-OV changed over to American-style 6.3 V valves from around 1938 but in 6.3 V guise it lived on into the 1950s as the KT61.
The mesh anode and remaining fragment of the Osram paper label.
The pinch and electrode supports. The control grid is wound on copper supports. The third grid is connected to the cathode.
A better view of the Osram label showing the gold and dark blue.
Looking straight down onto the dome reveals the suppressor grid wire.
A clearer view of the suppressor grid and the mesh anode.
The classic envelope is 44 mm in diameter and, excluding the B7 base pins, is 118 mm tall.
References: Data-sheet, private communication & 1043. Type KT41 was first introduced in 1937.