Mullard LF Green Ring

Mullard LF 'Green Ring'

Mullard LF Green Ring

BBC Mark

Electrodes

This pre-Phillips Mullard LF 'Green Ring' is a development of the ORA type. It still retains some traces of the green ring (visible at the left of the left-hand image above) which indicated it was suitable for low frequency amplification or detection. The BBC Mark means it was produced in 1923 or 4.

The construction is very primitive. It has a plate anode, with a single support, and a serpentine grid supported at both ends, very similar to the very earliest triodes, except that both these elements are formed into a U-shape. The filament is a simple semicircular arch in the centre of the U-shape. This complex geometry with a hugely varying grid-cathode distance probably gave this valve very non-linear characteristics, making it very suitable for anode bend detection.