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.
All three of our KT2 exhibits are housed within slightly different shaped envelopes and this design looks to be the earliest of the three.
With an anode load of 17,000 Ohms, a single valve would produce 0.5 Watts from battery supplies.
The Marconi brand name and Type designation. The lettering shows cracking and other signs of wear.
Looking down into the anode space the grids and filament can be seen. The filament at the top is broken and the part attached to the tension spring has opened out.
The top mica showing the grid supports held in place and the tension springs with hooks to hold the filament.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 96 mm tall.
References: Datasheet & 1040. Type KT2 was first introduced in 1937.