The VR118 (commercial 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 The test results and the service Type designation of VR118
Indistinct lettering on the glass.
The enhanced image shows the old stores code of 10E/88 plus Made in England.
The top mica. The twin inverted V filaments can be seen to be oxide coated as they are supported in the hook of the helical tension springs.
Looking down into the anode cavity. The anode diameter is much larger than beam tetrodes.
The classic envelope is 45 mm in diameter and, excluding the B5 base pins, is 94 mm tall.
