The 6GU7 was designed for use in the matrixing circuits of colour TV receivers. It is said to also be useful in phase inverter, multivibrator circuits and as a general purpose amplifier.
The RCA logo.
The twin triode sections with heat radiating fins on the tops of the control grids.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 59 mm tall.
Reference: Data-sheet. Type 6GU7 was first introduced in 1963. See also1963 adverts.