Sensibly equivalent¶ to:
20A3 4G/280K 5121 5727 ASG5121 CV797 E1955 EN91 G4S2 PL21 PL2D21 QX21 Ste1300/01/05 WT-210-0001
The 2D21 thyratron is, as usual, a gas filled valve, in this case the gas at low pressure is xenon. 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.
Mandy Malcolm writes: assisting the rebuilding of an APS-13 radar from 1944 that uses two 2D21's. This gives confirmation of the date of introduction.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 44 mm tall.
References: Data-sheet & 1040. Type 2D21 was first introduced in 1944.
Absolute Maximum Operating Conditions¶
Updated October 06, 2020. shape:thin.glass.tube construction:all.glass type:thyratron age:1950.1960 base:b7g heater:6.3v pins:7 pin:1.g1 pin:2.k pin:3.h pin:4.h pin:5.g2 pin:6.a pin:7.g2