The S6F33 is a special quality version of the 6F33 RF pentode, the structure is open with the anode being formed by two small plates that are strapped together. The suppressor grid is closely spaced and the valve has a very short suppressor grid control curve.
The maximum anode dissipation is 3 Watts and the fine wire screen grid dissipation is up to 1.5 Watts.
The two small anode plates connected by the strap in the foreground. The suppressor grid is close wound and probably useful as a second control grid. The actual control grid is placed very close to the cathode within the winding of the screen grid. All visible in this image.
The S6F33 is identical to the specification for the CV4064. At the top is the control grid radiator.
The thin glass tube envelope is 18 mm in diameter, and excluding the base pins is 45 mm tall.
References: Data-sheet, 1040 & Ray Cooper. Type S6F33 was first introduced in 1961. See also1961 adverts.
