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The 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 thin glass tube envelope is 18 mm in diameter and, excluding the B7G base pins, is 45 mm tall.

References: Data-sheet & ¹⁰⁴⁰. Type EN91 was first introduced in 1944. See also 1944 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.