The KT2 is a 'critical-distance' tetrode, based on the Harries patent. This type of tetrode requires a large anode diameter and is efficient only in relatively low-power applications. The famous kinkless tetrodes (KT66 etc.) are aligned-grid beam tetrodes with smaller anode spacings but capable of very substantial power outputs for their size.
The KT2 was in neither a beam tetrode nor a member of the KT66 family, except in name. The KT24 is essentially a beefier (and greedier) version of the KT2. The KT2 was introduced as a replacement for the PT2.
With an anode load of 17,000 Ohms, a single valve would produce 0.5 Watts from battery supplies.
The classic envelope is 42 mm in diameter and, excluding the B5 base pins, is 90 mm tall.
References: Data-sheet & 1040. Type KT2 was first introduced in 1937. See also 1937 adverts.