Large glass vacuum radio valve with black bakelite base and metal cap electrode at the tip. The internal metal components (plate, cathode, and grid assembly) are clearly visible through the bulb. The base features six metal pins for connection.
This model, a 6V6 GTA, is an audio power amplifier tube commonly used in military communication and signal equipment, including transmitters and field radios. It was housed within the Case Spare Valves No. 4L (Accession 2020.658) as part of a portable maintenance kit for field operators.