The GT1C thyratron is from the late 1930s and was used in timebases for Radar. The worlds first computer, Colossus, used these thyratrons as pulse generators. The operating speed of Colossus was 5,000 cycles per second.
At a defined grid voltage a Thyratron will rapidly switch to full conduction. The valve is turned off by reducing the anode voltage. 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 envelope has the etched Type designation within the distinctive M-OV oval lozenge.
The Marconi name etched into the glass envelope.
A closer view of the electrodes. The heater wires can be seen entering the cathode at the lower part of the image. The trigger electrode is in the centre.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 102 mm tall.
References: Datasheet, 1040 & 1043. Type GT1C was first introduced in 1937.