The GL446A from GE is what the Americans call a lighthouse tube because of its appearance. The 2C40 was the successor.
The cathode with its flat top is placed in close proximity to the wire mesh grid, that connects to the middle ring. The anode protrudes down the top glass cylinder and almost touches the grid. This follows the pattern of most high frequency planar triodes. So called because the operating area is all in the one plane and the electrodes have a very small physical separation.
Most of the European devices had co-axial connections unlike the conventional base used by General Electric. The 1951 data book has this listed but later editions do not.
The GL446A used as a microwave mixer at a wavelength of about 10 cm. Image courtesy of E G Bowen from A Textbook of Radar chapter XII published 1954.
The GE Logo.
The US Navy anchor. The very small gap between the cathode at the bottom and the grid above can be seen. To achieve performance at microwaves the inter-electrode spacing has to be small.
The grid disc with internal metal mesh.
The grid.
The mesh grid seen from the anode side.
A closer view if the woven wire grid.
The first thin glass tube envelope ring is 17 mm in diameter and excluding the IO base pins, the valve is 49 mm tall.
