Most VT52's are made within a classic envelope as one would expect from a 1930's valve. This American exhibit is in a tubular envelope.
The VT52 was a particularly economical audio power valve (heater power = 1.26 W) 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. We are uncertain whether it is numbered in the RAF or POVT series but we suspect the latter since it is a late 1930s valve.
As a single ended output stage the power is 2.8W, suitable for audio output in a transceiver. When operated in push pull the pair can deliver 7 W at 1.5% distortion. This could be used for a transmitter modulator for a low power phone transmitter.
The etched details. In addition to the VT52 there is the UK old stores code of 10E/11398. The hyphen should be ignored as the American VT-52 is a triode.
Above the pinch can be seen a heat sink fin between the copper control grid supports. The anode has a side flange for greater radiating area.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 95 mm tall.
References: Datasheet & 1043. Type VT52 was first introduced in 1940.