The CV8158 (commercial EN91) is a xenon filled thyratron valve and previously known as Type 2D21. This example is of tetrode construction and was designed for relay or grid-controlled rectifier applications.
When a certain critical anode current flows the ionisation of the gas begins an avalanche discharge that overrides the grid control and leads to saturation current flow. The anode current can then only be extinguished by reducing the anode volts below the ionisation threshold.
The gm value in a normal hard valve is replaced by the control ratio parameter. In this valve the ratio is 250. At saturation the valve voltage drop is 8 Volts.
The box anode covers the internal electrodes. Note the ceramic tube screening the anode lead.
The face view of the anode box.
The thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 47 mm tall.
