The EC52 is a small transmitting valve from the early days of all glass construction. It was designed for VHF operation, and probably mobile equipment. It was originally given the Type designation of RL16.
The picture shows the flattened oxide coated cathode and the gold grid wire can also be seen. The anode is carbonized. The whole electrode assembly takes up less than half of the envelope, and a second valve could be physically fitted into the envelope.
The wide glass tube envelope is 30 mm in diameter and, excluding the B9G base pins, is 55 mm tall.
References: Data-sheet, 1040 & 1043. Type EC52 was first introduced in 1941.