The DET29 disc seal valve
The cathode is in the form of a thimble coated on the end, while the grid is composed of parallel wires tightly stretched across a hole in a metallic disc and the anode is a plain flat disc, the various parts being spaced by means of glass or ceramic seals. The outer rims of the discs extend beyond the seals for connection to the external circuit which can advantageously be of cylindrical co-axial form to suit the construction of the valve.
Such valves are intended for use in grounded-grid circuits and will operate up to frequencies of several thousand megacycles with quite good efficiencies: they are available both as triodes and as tetrodes. The anode is generally cooled by an air blast through radiating fins or by conduction to the external coaxial circuit elements. Valves of this form are also known as planar.
In the ceramic stacked triode the electrode discs are sealed directly to accurately machined ceramic washers. The valve can give 15 db gain at 1000 MHz with a noise factor of 8.5db.