The KT63 was originally the N63, and was released in the IO based form in 1937. It is an audio output beam tetrode valve. The base cap with plastic insert and metal shell is an M-OV feature.
The anode load should be 7,000 Ohms.
The reverse is plain in this exhibit.
looking at the top mica, the cathode is round and the control grid has cooling fins. The small flaps folded over are the top of the beam forming plates.
The two beam plates are strapped together and connected to the cathode. The folded seam in the anode can be clearly seen as can the wire grids and the white cathode tube.
The classic envelope is 45 mm in diameter and, excluding the IO base pins, is 103 mm tall.
References: Data-sheet, 1040 & 1043. Type KT63 was first introduced in 1937. See also1937 adverts.