The NGT2 thyratron was based on the commercial GT1C and was later known as the CV1128. It was a development of the NGT1 and the NG indicates that this was made for the Royal Navy. The VGT128 was the RAF designation.
This thyratron is from the 1930s and was used in timebases for Radar and television. At a defined grid voltage the valve, will rapidly switch to full conduction. The valve is turned off by reducing the anode voltage. Most thyratrons are gas filled and can be considered as triggered gas discharges. The precision of construction gives the defined and reproducible operating characteristics. This valve not only has a high peak current but is designed for operation at up to 8,000 pulses per second.
The first computer, Colossus, used these thyratrons as pulse generators. The operating speed of Colossus was 5,000 cycles per second.
The heater can be seen on the right.
The anode is fitted with both top and bottom caps to keep the discharge within.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 102 mm tall.
References: Datasheet, 1040 & 1043. Type NGT2 was first introduced in 1937.