The D63 is a double signal diode with separate cathodes. The old service code was ARDD3 and the later CV code was CV1301.
The Marconi name and the Marconiphone Company name on the zinc paint. This exhibit had never been unwrapped and inside the paper and corrugated card wrapping it was clear that the paint was falling off.
The paint from the top of the valve detached in a single piece. Other parts of the paint flaked off.
The outside of the top paint. Note the white corrosion around the break. The assumption is that this valve has been exposed to damp over time.
As the paint came away the inner structure became visible.
The the central screen has the ends bent at right angles forming a Z shape. Each diode is formed as a separate valve section much as a double triode would be made.
The flat metal in the centre is one end of the screen. The diode sections are on either side.
A closer view of one diode. The size of the anode seems excessive for a maximum current of 2.0 mA.
The diode section end view. The adhesive residue on the glass reduces the clarity of the image.
Top view: each cathode tube has four strands of heater passing through it.
In this enhanced image the diode structure is clearer and the adhesive residue on the glass is also easy to see.
The classic envelope is 35 mm in diameter, and excluding the IO base pins is 76 mm tall.
References: Datasheet, 1040 & 1043. Type D63 was first introduced in 1937.