The TD03-10G is an indirectly heated disc seal triode, without internal feedback, primarily intended for use as a common grid, earthed anode, concentric line oscillator. It has a 10 Watt anode dissipation and can also be used as a power amplifier. We have no details of this specific variant.
The grid ring leads to a frame of thin wires with the cathode and anode mounted close to it on opposite sides.
The co-axial cathode and heater connection can be seen inside to lead to an insulated heater and the flat topped cathode cylinder. The underside of the frame grid is also visible. Wound under tension the fixed loops are then cup to leave a single layer of wires.
The planar envelope is 15 mm in diameter and, including the base pins, is 60 mm tall.
References: Data-sheet & 1040. Type TD03-10G was first introduced in 1957.