The D.3 design from Mullard dates from 1924 and was a replacement for the bright emitter LF ORA. The D.3 is a dull emitter triode and the two green rings denote the LF variant. Other variants included one with two red rings for HF use also introduced in 1924 and the detector with two white rings introduced in 1925.
The D.3 AF had a μ of 7.
The D.3 differs from the D.06 in that the latter was designed with a 3.0 V 60 mA oxide coated filament whereas the D.3 range have thoriated tungsten filaments.
The above image enhanced to show more of the etched lettering.
The reverse carries the Mullard logo.
Enhanced to reveal more detail.
Etched lettering on glass with a mirror surface within gives a double image.
The wording is Protected by Patents.
The silvered inside of the envelope obscures the inner detail. The electrodes are mounted at about 30 degrees to the vertical and can only be seen by looking up from the base with the valve almost horizontal.
The bright anode cylinder with helical grid and single strand filament.
The filament running from a restricted constant current source.
The filament at 300 mA.
Taken with the microscope to show the geometry.
With dark-field illumination the third BBC stamp is revealed. This dates the valve to between 1924 and 1927 as expected.
Illumination as above.
μ-Tracer plot of the basic characteristics. The anode is run at 100 Volts.
Special thanks to John Barber for allowing the museum to borrow his D.3 set.
The balloon envelope is 35 mm in diameter and, excluding the B4 base pins, is 85 mm tall.
Reference: 1003. Type D.3 was first introduced in 1924. See also1924 adverts.
