The VT269 is a most interesting valve. It was made in America on 31st January 1944 and packaged in a buff cardboard box. It was made for military service with the US Army and Navy.

The valve is a type 717A is known as a 'little doorknob'. VT269 is a US Government designation (nothing to do with the RAF).

Intended as a low-noise front-end amplifier in UHF radar receivers, the 717A achieves 4 mA/V despite its small size. Designed by Western Electric, the 717A was made in large numbers by several US manufacturers during WW2. It was a successful valve although it was soon superseded by improved (and cheaper) all-glass types.

The inset photograph shows the construction, this sample arrived with a broken envelope, and thus afforded a close view of the electrode assembly. For scale the width between the flats in the base circle is 9 mm. The picture shows indirectly heated cathode, three wire wound grids on notched rods and a cylindrical anode. This pentode lays flat across the pressed glass base of the envelope and the electrode structure is small enough to fit into the B7G miniature envelope that was introduced into the UK after WW2. This design is a hybrid between traditional construction and the all glass valves. Similar experimentation is shown the the metal valves from 1935.

The balloon envelope is 34 mm in diameter and, excluding the IO base pins, is 37 mm tall.

This exhibit was last updated on 02 December 2007