The VT25 directly heated transmitting triode has a large four pin base and was made for the RAF. Originally the VT25 had a carburised thoriated tungsten filament that proved fragile in airborne applications. The filament was replaced by an M shaped oxide coated filament on a nickel ribbon. The anode box is quite large and carbonised to radiate heat and larger than the original as the oxide filament was both wider and gave greater emission and thus greater power. The ceramic insulators and special base suggest a high operating voltage. Operating frequency would be in the HF range and probably the output power was of the order of 50 Watts.

The original valve was from M-OV and a development of the DET1.

The John Lawrence collection has three of these valves, each from a different manufacturer.

The wide glass tube envelope is 52 mm in diameter and, excluding the L4 base pins, is 160 mm tall.

Reference: ¹⁰⁰⁵.

 
Pin Connections

L4	1	2	3	4
	a	f	f	g1

 
Absolute Maximum Operating Conditions^¶

Triode	Vh	Ah
	6.0	1.9

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