The D.06 is a dull emitter triode from Mullard. The D06 was made in three variants, the first D.06 had two green paint rings and was for audio amplification, the D.06 version with two white rings was for use as a detector, the one shown here with two red paint rings was a high impedance type designed for high frequency use as an amplifier or detector.
The D06 trio of valves were introduced as a development of the DF.ORA.
The other side of the valve carries the type designation and the BBC logo. The D.06 was introduced in 1924.
Although the silver gettering obscures the electrode construction it is possible to obtain a glimpse of the anode cavity. The anode is a Nickel cylinder but the control grid and filament can not be seen.
Our exhibit came in its original box and the packing of the valve was a horse hair mat.
The operating conditions for the valve were published on the side of the box showing that at the time valves were not just supplied to set makers but that enthusiasts were also a key market.
The Balloon envelope is 33 mm in diameter and, excluding the B5 base pins, is 85 mm tall.
Reference: Data-sheet & 1003. Type D.06 was first introduced in 1923. See also1923 adverts.