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In order to obtain amplification over a wide band of frequencies, a tube having high transconductance and low input and output capacitance is required. A grid-controlled inductive-output tube having these attributes and giving 10 watts output at 500 megacycles is described. A high ratio of transconductance to input capacitance is attained by close cathode-grid spacing and large grid-screen spacing, the latter made possible by use of a very high screen voltage. A low output capacitance is obtained by the use of an inductive-output arrangement which requires no power dissipation by the output electrodes. The design of the output circuit for low inherent capacitance is facilitated by the use of magnetic lenses to focus the electron beam. These lenses can be energized by a permanent magnet. Loading caused by secondary electron emission from the current collector is eliminated. The performance of the tube as a wide-band amplifier is described.