This miniature signal diode was made for military use, probably used as a detector in Radar IF chains. The civilian equivalent is the D1.

The shaped anode plates leave a tubular hole for the cathode assembly. The anode plate fins clamp round support rods for stability. Mica top and bottom plates complete the construction.

As well as 3 pin bases these small signal diodes were also held in plastic housings similar to fuse holders. The valve would push horizontally into the clips at both ends of the valve holder.

The thin glass tube envelope is 11 mm in diameter, including the B3G base pins, is 45 mm tall.

References: Datasheet, ¹⁰⁴⁰ & ¹⁰⁴³. Type VR78 was first introduced^¶ in 1937.

 
Pin Connections

B3G	1	2	3	tc
	h	k	h	a

 
Absolute Maximum Operating Conditions^¶

Diode	Vh	Ah	Va	mAa
	4.0	0.2	125	5

Thanks to Frank Philipse for supplying the above PDF datasheet