The DFA range of triodes was designed for the output stages of broadcast receivers. The box describes the DFA1 as for power amplification to drive the largest loudspeakers. In 1924 when the DFA1 was issued the speaker would have been of the moving iron or reed type and probably fitted with a horn.
The details are etched into the glass as well as around the base.
The type three BBC trade mark stamp on the glass dates this exhibit to between September 1924 and 1927. The nickel base cape suggests the earlier part of the period.
Unlike our other DFA1 the gettering stops short of the base allowing a view of the electrodes.
The vertical bright box anode with grid wires wound on two stout supports. No filament is seen in this image.
The balloon envelope is 53 mm in diameter, and excluding the B4 base pins is 101 mm tall.
References: 1003, Data & 1043. Type DFA1 was first introduced in 1924. See also1924 adverts.
