The RS242X is a transmitting triode with a 12 Watt anode dissipation. The 'X' variant has a slightly greater heater power. The earlier and larger RS241 (also on the data-sheet) has a smaller heater power than the RS242 design but larger anode dissipation. The RS242 looks to be a more efficient design with a higher peak cathode current, requirements for Class C transmitters, especially for morse (CW)transmission.
The 3.8 Volt filament voltage can be seen marked on the envelope near the base.
The valve carries the word Kriegsmaring (navy).
The side view, also showing the getter holder and filament tension springs at the top.
In this image the filament can be seen as can the control grid. Also clearly seen are the welds fixing the pre-assembled electrode assembly to the pinch connections. The anode support rods pass to a collar around the pinch stem that is held in place by a nut and bolt.
The evacuation hole in the pinch stem and the anode support collar.
The dome and top mica. The filament tension springs are held by the mica. In this image the filament can be seen to be oxide coated and that the filament is a ribbon not a wire.
A close-up of the top mica assembly, clearly showing the filament as a ribbon.
The Type is followed by the suffix IX but the variant should be just X. Is this a special?
The balloon envelope is 51 mm in diameter, and excluding the B4 base pins is 97 mm tall.
Reference: Data-sheet. Type RS242X was first introduced in 1935.