The TD03-10 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.
This shows the central grid with the copper anode on the right. The grid is formed from a parallel series of wires across the central hole. It looks as if the grid wires are held in a sandwich between two copper discs. In the picture the wires run from top left to lower right.
An overall view with heater connection at lower right.
The planar envelope is 16 mm in diameter, and is 62 mm overall.
References: Datasheet & 1040.