The CV1756 magic eye tuning indicator is from RCA who designed the first such tuning indicator in the 1930s. The operating characteristics for this exhibit are the same as for type 6E5. The american service code is VT-138 and this is the designation stamped on the base.
The domed end window seen straight on.
The end window with target components together with the triode amplifier on the left closer to the base.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 83 mm tall.
References: Data-sheet & 3002. Type CV1756 was first introduced in 1942.