NT57T

NT57T silica valve, with anode (left) and grid (right) wire connections at the top, and filament at the bottom, also wire connections only. This valve has two 'hairpin' filaments, each with a pair of wires. The NT57T is the thoriated filament version of the NT57, the first valve to be made specifically for use in radar. The NT86, developed from the NT57T, had three filaments. The use of thoriated tungsten resulted in the increase of cathode emission to 18 A from the 5 A emission of the NT57. Heating power was about 300 W against the some 700 W of the NT57.

Silica glass has a very high melting point (between 1500 and 1700 C) and a low coefficient of thermal expansion. Normal glass softens at around 450 C. Because of these properties, silica glass does not crack by heat.

The picture of this valve features on the cover of the August 2003 issue of "The Collector", published by the "Tube Collectors Association".

Early samples of the NT57T were made and tested in April 1939 into a Type 79 early warning radiolocalization set at the HM Signal School in Portsmouth. By September 1939 the tube was in small-scale production at Signal School and MOV.

Also known as 10E/93

Collection of