The CV5042 double triode is pin compatible with the ECC81, ECC82 and ECC83 series from Mullard but has slightly different characteristics. Brimar make the commercial equivalent 12BH7 and give the design use as TV frame oscillator and frame output. The CV number suggests a rugged or reliable version.
The identical box anodes seen side on. The getter holder can be seen rising from the right hand anode support.
The anode sheets are stitched together. The copper grid supports can be seen as can the lower and upper portions of the grid winding.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 58 mm tall.
References: Datasheet & 1040. Type CV5042 was first introduced in 1950.