The D.3 design from Mullard dates from 1924. It is a dull emitter triode and the two red rings denote the HF variant. Other variants included one with two green rings for LF (AF) use also introduced in 1924 and the detector with two white rings introduced in 1925.

The D.3 HF had a μ of 17 whereas the other two had amplification factors of seven.

The electrodes are mounted vertically at an angle. The cylindrical anode has a spiral grid within and a single strand filament running through the centre.

The balloon envelope is 35 mm in diameter and, excluding the B4 base pins, is 81 mm tall.

 
Absolute Maximum Operating Conditions

Triode	Vh	Ah	Va	Vg	mAa	ra	gm
	2.0	0.3	50-125	-	-	60,000	0.28

This exhibit was last updated on 02 December 2007