Lighthouse Tube

a triode for use at ultrahigh frequencies, the vacuum envelope of which resembles a lighthouse tower.

The lighthouse tube is used as an oscillator or amplifier in the decimeter and centimeter wavelength ranges. In order to reduce the electron transit time between electrodes and decrease the inductances of their terminals (the inductances being a major obstacle to raising the maximum operating frequency of an electron tube), the interelectrode distances of the lighthouse tube are made very small (fractions of mm), and the terminals are made of flat metal disks of various sizes welded to the end faces of glass cylinders. The edges of these disks, which remain outside the vacuum envelope, are connected to a detachable part of the oscillatory system (sections of coaxial line). The first lighthouse tubes, which were manufactured in the 1940’s, had maximum operating frequencies of 3.3 gigahertz and output powers of 30-150 milliwatts. Since the 1960’s superior metal-ceramic tubes have been used instead of lighthouse tubes in radio equipment.