The 8A8 is from the era of VHF Band III television in the mid 1950's. The valve is a triode pentode, with separate cathodes, designed to function as a mixer and oscillator in the tuner or converter if used with an older Band I television. In the UK Band III television started in 1955.
This view is of the pentode looking across the grids. The plate behind is the inter-section screen.
The screen is in the centre with the pentode on the right and the triode to the left.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
References: Datasheet & 1040. Type 8A8 was first introduced in 1954.