The PCF802 was designed as the first stages in television line frequency generation prior to the line output stage. The pentode is described by Mullard as the oscillator while the triode is for service as a reactance valve. This suggests the triode acting as a frequency controlling stage.
This image is of another example of the PCF802 and reveals greater detail.
The pentode on the left is oriented at 90 degrees to the triode on the right.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 46 mm tall.
References: Data-sheet, 3002 & 1040. Type PCF802 was first introduced in 1962. See also1962 adverts.