This miniature signal diode was made for military use as a detector in Radar IF chains. The civilian equivalent is the D1.
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 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.
The Type designation. The insulated heater can be seen entering the round cathode tube.
The thin glass tube envelope is 12 mm in diameter, including the B3G base pins, is 47 mm tall.
References: Data-sheet, 1040 & 1043. Type VR78 was first introduced in 1937. See also1937 adverts.
