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2D21

Sensibly equivalent to:
20A3 4G/280K 5121 5727 884 885 ASG5121 CV797 E1955 EN91 G4S2 PL21 PL2D21 QX21 Ste1300/01/05 WT-210-0001
See also:
Mufax Chart Recorder Maintenance Manual - CV797 short entry
    
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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.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 44 mm tall.
References: Datasheet & 1040. Type 2D21 was first introduced in 1952.

 

Pin Connections
B7G
1
2
3
4
5
6
7
g1
k
h
h
g2
a
g2

 

Absolute Maximum Operating Conditions
Thyratron
Vh
Ah
Va
mAa
6.3
0.6
650
500
Thanks to Frank Philipse for supplying the above PDF datasheet.
Updated April 07, 2015.
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