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Small gridded-tube characteristics for cw applications are compared with other microwave devices in Table 2. For pulse work, transistors and varactors are not even in the running at the moment. The tube can be easily pulsed to provide a 1000-to-1 improvement in power output over cw conditions. Solid-state devices are not presently suited to pulse service; and in some cases, their maximum pulse voltages and currents cannot exceed the cw ratings.

Certainly a comparison of gridded tubes and solid-state devices is subject to change. The solid-state art is advancing rapidly, and any comparison could be obsolete before it was published. The current state-of-the-art is reflected in the curves of Fig. 11, which represent an updating of previously published curves.

Advantages of gridded triodes

Gridded tubes are applicable to many microwave systems. Features of these tubes include: low cost, small size and weight, simply circuitry, good tolerance to adverse environments, high pulse power output and low oscillator sideband noise (FM and AM), high gain-bandwidth at high power, high over-all efficiency at high frequencies, low cross and intermodulation and fast rise and fall times at high voltages.

Who makes them?

Aside from G.E., companies that possess ceramic planar-tube know-how include Amperex, Eimac Div. of Varian, Machlett, RCA, Siemens and Halske, and Sylvania.

Admittedly, some of the state-of-the-art described here is found only in experimental tubes. But demand could bring most of the indicated performance into the open.