The GT3 is a thyratron and it looks like a successor to the GT1C although sources differ as to peak current capability. The GT1C data-sheet gives an average current of 300 mA the same as the GT3. It is probably safe to say that the GT3 is effectively the same valve but on an IO base with a 6.3 Volt heater.
The anode completely enclosed. The reverse side of the envelope just displays the GEC logo. The branding as GEC denotes a valve for industrial or professional use.
The wide glass tube envelope is 38 mm in diameter, and excluding the IO base pins is 76 mm tall.
Absolute Maximum Operating Conditions¶
Updated January 23, 2013.