This exhibit is clearly marked as being a Type EL38R but no details can be found of this Type. The EL38 is a late 1940s tV line output valve and the construction differs from this valve and the heater runs at 1.4 Amps so either this has a more efficient heater or the peak cathode current is less. The heater requirement for this exhibit was measured at the museum.
Does this view look familiar? It looks just like the squat 807 with the exception of the base. The 807 is on the UX5 base whereas this is on the International Octal base just like the 6L6G that the 807 was based on.
The lower screen has the oval shape normally only seen on the 807.
The valve on the left is the 807 and EL38R is on the right. Apart from the visual similarities the differences lie with the base cap and the top cap. The top cap of the 807 is 8.5 mm diameter whereas the EL38R has the normal domestic top cap with a diameter of 6.3 mm.
The classic envelope is 50 mm in diameter, and excluding the IO base pins is 122 mm tall.