Long-Life Grid-Controlled Amplifier.

Techniques were evolved that permit a tungsten grid to be securely bonded to a porous tungsten cathode disk. A thin film of boron nitride insulation is first deposited directly on the cathode surface. Then a thin layer of tungsten is deposited over the surface of the boron nitride. An alumina particle erosion technique is used to form a grid pattern in the tungsten and boron nitride layers thereby exposing again the cathode surface. Oxide coating is finally impregnated into the pores of the tungsten disk. The resulting assembly is well insulated, structurally sound and capable of providing thermionic emission. However, a change in the method of preparation of the tungsten disk will be required in order to attain the desired high level of thermionic emission from the cathode. When this is achieved, computer studies indicate that high-power broadband operation can be expected by use of input circuits designed to accommodate the larger input capacitance inherent in the bonded grid construction. Author