Receiving Tubes

electron tubes designed mainly to amplify and detect electrical signals, to convert frequencies, and to rectify and generate low-power electrical oscillations in various radio receivers, amplifiers, and measuring circuits. Electron-beam indicator tubes, electrometer tubes, and mechanotrons are also classified as receiving tubes. Receiving tubes have a low noise level, a high transconductance, a high input resistance at frequencies up to several gigahertz, and a low interelectrode capacitance. Because of these advantages, such tubes are capable of linear amplification and nonlinear conversion of very weak oscillations, at frequencies from zero (direct current) to several gigahertz, with practically no power consumption in the circuit of the control electrode, usually a grid.

Receiving tubes are subdivided according to a number of characteristics into several groups. One classification is based on the number of electrodes and comprises vacuum-tube diodes, including low-power kenotrons and damping diodes, triodes, tetrodes, pentodes, hexodes, heptodes, pentagrids, and octodes. Another classification is based on the method of heating the cathode and includes directly heated tubes, using direct current, and indirectly heated tubes, using alternating current. A third classification is based on the design and external dimensions and includes several series, each having tubes with identical appearance, dimensions and shape of connecting components, diameter, and envelope material but each consisting of a set of tubes with a differing number of electrodes. Examples of such series are miniature glass tubes with a base, glass tubes without a base (bantam tubes), glass microminiature tubes with flexible terminal leads and envelope diameters of 13, 10, 6, and 4 mm, tubes with metal-ceramic envelopes, including titanium-ceramic, tubes of the nuvistor type, and multiple tubes that contain in one common envelope two or more systems of electrodes with independent electron beams, such as double diodes, triodes and beam power tubes, diode-triodes, and triode-pentodes.

Receiving tubes have several basic engineering parameters. The cathode-heating voltage is most often 1.2, 2.0, 6.3, or 12.6 volts (V). The cathode-heating current is usually 0.03, 0.1, 0.15, or 0.30 ampere. The electrode voltage ranges to 300 V; the inverse voltage of high-voltage kenotrons and damping diodes may be as high as 35 kV. The anode current ranges to 150 mitliamperes (kA) and for low-power kenotrons can reach 400 mA. Maximum plate dissipation ranges to 25 watts. Transconductance is approximately 1 to 40 mA/V, and the amplification factor is approximately 5 to 2,000. Plate resistance varies approximately between 1 × 10³ and 2 × 106 ohms. The noise-equivalent resistance is of the order of 100 ohms or higher, and tube life may be 1,000, 2,000, 5,000, or 10,000 hours or longer. Permissible acceleration under vibrational loads may exceed 30 g, and the operating temperature ranges from —60° to +200°C for tubes with glass envelopes and from —60° to +500°C for tubes with ceramic envelopes. Permissible humidity is 98 percent at 40°-50°C, and there are indexes of resistance to other ambient conditions as well.

Since the 1960’s and 1970’s, receiving tubes have been increasingly replaced by semiconductor devices. However, receiving tubes retain a number of advantages, the most important of which are the ability to operate in a wide range of temperatures with no substantial change in parameters and high radiation stability. The development of new receiving tubes is aimed at reducing their outside dimensions and improving their parameters and characteristics, including the operating temperature.