Virtual Valve Museum

Virtual Valve Museum

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GT1C / CV1128 / NGT2 / VGT128 / 10E/15 triode thyratron, and GT1CSS solid-state replacement


Size This valve measures 114x45mm overall and has a 5-pin base.

This thyratron found many uses as a timebase for radars, and in particular many were used in the Colossus computer which was used at Bletchley Park to crack the codes of the German Lorenz cipher machines. See, and for further information.

Heater voltage 4V
Heater current 1.4A
Max anode voltage 500V
Max peak anode current 1A
Max mean anode current 300mA
Grid control ratio 28
Max anode-cathode voltage drop 16V


Pin Function
1 Anode
2 Grid
3 Heater
4 Heater
5 Cathode

Left: GT1C; centre: NGT2; right: CV1128; bottom: NGT2 GT1C label, a similar label is carried on the VGT128

GT1C NGT2 CV1128
GT1C label on the NGT2
Solid state GT1CSS
Top quarter view Bottom quarter view