The D.06 was released in three versions, this one has two green rings and was designed for use as an AF amplifier. The D.06 with two red rings and was designed for HF use and had a higher impedance. The D.06 with two white rings was designed as a detector. All types had the 3 V 60 mA filament rating.
The third style of BBC stamp is etched onto the envelope. Thus this exhibit dates from 1924 to 1927.
The D06 design was introduced as an improvement to the DF ORA that was also released in 1924. The DF ORA also had a 3 V 0.06 A filament.
When Mullard introduced the D.06 range it also released the D.3. The D.3 was electrically identical to the D.06 with the exception of the filament which in the case of the D.3 was a 2 V 0.3 A type. The single accumulator 2 V filament supply was a standard and the the use of two dry cells to power the D.06 was new.
The Mullard Logo. The pinch is just visible and looking up into the envelope a small diameter vertical cylindrical anode inclined at an angle can just be seen.
The base with lead-out wires soldered to the split pins below the composition base.
The balloon envelope is 35 mm in diameter, and excluding the B4 base pins is 86 mm tall.
Reference: Data-sheet & 1003. Type D.06 was first introduced in 1923. See also1923 adverts.