The DFA8 is a battery triode audio output valve and was marketed as suitable for the intermediate stages of large power amplifiers
The anode is a flattened box, ribbed to add strength and left bright.
Full details are etched into the dome of the envelope. The grid supports bend outwards and are held in a glass rod. This insulated rod doubles up as a support for the filament tension spring. The filament is a single inverted V.
The anode is formed from a pair of plates. The grid is wound on notched rods. The filament looks to be a thoriated tungsten wire.
From the pinch it can be seen that the pre-assembled grid is spot welded to the wire emerging from the pinch. The anode appears to be crimp fixed onto its support wire.
A closer view of the top support.
The moulded base has the anode pin clearly marked.
The balloon envelope is 52 mm in diameter, and excluding the base pins is 117 mm tall.
Reference: 1043. Type DFA8 was first introduced in 1927. See also1927 adverts.