Characteristics of vacuum tubes for radar intermediate frequency amplifiers

The desired characteristics for vacuum tubes for use in broad-band intermediate frequency amplifiers are primarily high transconductance, low capacitances, high input resistance, and good noise figure. These characteristics determine the frequency bandwidth, amplification, and signal-to-noise ratio attainable with such an amplifier. The maximum operating frequency is generally limited by the input resistance of the tube which decreases as the frequency is increased, and, in some cases, by the tube noise which increases with increasing frequency. Three other characteristics which are also important are small physical size, low power consumption, and ruggedness. The present paper describes how these characteristics are related to the performance requirements for intermediate frequency (IF) amplifiers used in radar systems and shows how the requirements were met in the design of the Western Electric 6AK5 Vacuum Tube.