The DH63 is a double diode triode with the control grid brought to the top cap. The design use was as detector and ACG rectifier together with first audio amplifier stage in receiver equipment.
The DH63M was the metallised version.
The GEC brand label. The GEC brand was the M-OV professional brand. The other sticker shows that this valve was last tested in 1991.
The outer diode screen with rod anodes within. The heater is wound as a double helix to cancel out as far as possible the AC induced hum on the output audio.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 91 mm tall.
References: Data-sheet, 1040 & 1043. Type DH63 was first introduced in 1937. See also1937 adverts.
