The A2900 is a double triode for use in applications where long life and close control of characteristics are essential. The data-sheet also gives details of pulse operation. Additionally the valve will maintain its emission after long periods of operation under cut-off conditions - essential for computer use.
The GEC brand was used for professional use valves.
The twin triode sections. Each grid has a heat radiating fin at top.
The central anode cavity has additional heat sinking in the form of side flanges.
The thin glass tube envelope is 20 mm in diameter and excluding the B9A base pins, is 48 mm tall.
Reference: Data-sheet. Type A2900 was first introduced in 1963.