Mercury-vapour thyratron: once the grid loses control and the tube fires, the grid cannot regain control until the anode voltage is removed or reversed.
Must be operated within the specified ambient temperature range to ensure correct mercury vapour pressure.
Allow adequate filament warm-up time (typically 30 seconds minimum) before applying anode voltage.
The Valve Museum describes the classic envelope as 45 mm in diameter and 128 mm tall (excluding base pins).
Anode connection is via the top cap (tc), not through the octal base.