The VT52 was a particularly economical audio power valve (heater power = 1.26W) and was used where very large numbers of valves were required (eg. in telephone exchanges), consuming power throughout the night when nothing much was happening but it was essential for the whole system to be instantly ready for an emergency.
Their power output capability was small by domestic radio standards but entirely adequate for a telephone line driver. The VT52 was used in very large numbers by the Post Office Telephones system but was also used to a smaller extent in Services equipment.
As a single ended output stage the power is 2.8 W, suitable for audio output in a transceiver. When operated in push pull the pair can deliver 7.0 W at 1.5% distortion. This could be used for a transmitter modulator for a low power phone transmitter.
The anode has four side flanges set at right angles and normal to the oval anode.
The control grid supports are topped with heat radiating fins.
The classic envelope is 35 mm in diameter and, excluding the IO base pins, is 93 mm tall.
References: Data-sheet & 1043. Type VT52 was first introduced in 1940.