This exhibit is an ECC86 double triode. It is very special high frequency double triode. At a time when AF power transistors were replacing valves but no VHF transistors were available the ECC86 was designed to operate directly from vehicle battery supplies for car radio applications alongside transistors.
One half of the valve. The depression in the anode is so the working face can be close to the grid but with lower capacitance than if the whole anode was that close.
The two sections are separated by a screen.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 49 mm tall.
Reference: Datasheet Type ECC86 was first introduced in 1959.