The NR38 is a vari-μ RF pentode and originally the specification was based on the VMS4 and the MVS/Pen. The CV register Type designation is CV1165.
Later valves would have had the top hat top connection. This exhibit with the screw top cap probably dates to the initial introduction of the type around 1933.
The internal coating shows little other than the pinch.
The B5 base and above the pinch the base support of the electrodes. The heater passes through the cathode tube four times.
The screw top cap that was obsolete by the mid 1930s.
The classic envelope is 44 mm in diameter, and excluding the B5 base pins is 117 mm tall.
