The KT2 is a 'critical-distance' tetrode, based on the Harries patent and made by M-OV. This type of tetrode requires a large anode diameter and is efficient only in relatively low-power applications.
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, this valve would produce 0.5 Watts from battery supplies when operated as a single valve in Class A. A pair of valves operating in quiescent push-pull could deliver one Watt.
The Osram label. Note the anode diameter.
The oxide coated filament and grids.
In this image the hard light reflects off the screen grid and the control grid can be seen in shadow.
The classic envelope is 45 mm in diameter and, excluding the B5 base pins, is 96 mm tall.
References: Data-sheet & 1040. Type KT2 was first introduced in 1937. See also1937 adverts.