Recent Developments in Miniature Tubes

The development of two indirectly heated miniature tubes, a triode and a sharp cut-off amplifier pentode especially suited for use at high frequencies, is described. The electrical and mechanical factors involved in the design and application of these tubes are discussed and their novel structural appearance is described. Because of their decreased lead impedances, interelectrode capacitances, and transit times, these miniature tubes allow considerable improvement to be made in high-frequency receiving equipment. It is possible to operate the triode as an oscillator in a conventional circuit down to a wavelength of approximately 40 centimeters. The pentode can be operated as a radio-frequency amplifier down to a wavelength of approximately 70 centimeteres. It is practicable to obtain stable gains with it of from ten to fifteen at three meters, a wavelength at which standard tubes are almost entirely ineffectual. Both tubes can be used, down to much lower wavelengths, in exactly the same manner and for the same applications that the corresponding conventional tubes are used; i.e., as oscillators, amplifiers, detectors, converters, and as negative-resistance devices. The small size of the tubes and their novel structural design allow compact and convenient receiving equipment to be built. Even at the longer wavelengths, they are applicable to a large nunmber of uses for which their excellent characteristics, small size, and low weight make them particularly useful.