For glass tubes, while the tube envelope is being evacuated, the internal parts except the getter are heated by RF induction heating to evolve any remaining gas from the metal parts.

The US names "vacuum tube", "electron tube", and "thermionic tube" all simply describe a tubular envelope which has been evacuated ("vacuum"), has a heater and controls electron flow.

Vacuum hardness and proper selection of construction materials are the major influences on tube lifetime. Of course, there are other sizes that will fit inside each other, but often with a good couple of millimetres ‘play’, and therefore we wouldn’t describe them as telescopic. Advances using subminiature tubes included the Jaincomp series of machines produced by the Jacobs Instrument Company of Bethesda, Maryland. Elimination of silicon from the heater wire alloy (and more frequent replacement of the wire drawing dies) allowed the production of tubes that were reliable enough for the Whirlwind project.

A vacuum tube needs an extremely high vacuum (or hard vacuum, from X-ray terminology [71]) to avoid the consequences of generating positive ions within the tube. The highest-power tube currently available is the Eimac 4CM2500KG, a forced water-cooled power tetrode capable of dissipating 2. Within commercial and domestic settings, steel pipe and tubing is used to manufacture appliances, as protective coverings for utility pipes, and within numerous fabrications and engineering projects.Since no current flows through a tube's grid connection, these batteries had no current drain and lasted the longest, usually limited by their own shelf life. Additionally, multi-factor authentication (MFA) support enables you to apply additional security without updating your enterprise applications. The RCA Type 55 is a double diode triode used as a detector, automatic gain control rectifier and audio preamplifier in early AC powered radios. Tubes designed for high gain audio applications may have twisted heater wires to cancel out stray electric fields, fields that could induce objectionable hum into the program material. Pliotrons were closely followed by the French type ' TM' and later the English type 'R' which were in widespread use by the allied military by 1916.

These devices became a key component of electronic circuits for the first half of the twentieth century. Most vacuum tubes have a limited lifetime, due to the filament or heater burning out or other failure modes, so they are made as replaceable units; the electrode leads connect to pins on the tube's base which plug into a tube socket.

They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers. Marconi had developed a magnetic detector, which was less responsive to natural sources of radio frequency interference than the coherer, but the magnetic detector only provided an audio frequency signal to a telephone receiver. Amplification by vacuum tube became practical only with Lee de Forest's 1907 invention of the three-terminal " audion" tube, a crude form of what was to become the triode. A negative temperature coefficient device, such as a thermistor, may be incorporated in the equipment's heater supply or a ramp-up circuit may be employed to allow the heater or filaments to reach operating temperature more gradually than if powered-up in a step-function.

Main article: Triode The first triode, the de Forest Audion, invented in 1906 Triodes as they evolved over some 45 years of tube manufacture, from the RE16 in 1918 to a 1960s era miniature tube Triode symbol.Traveling-wave tubes (TWTs) are very good amplifiers and are even used in some communications satellites. The dynatron region of the screen grid tube was eliminated by adding a grid between the screen grid and the plate to create the pentode. Where 230 V nominal mains voltage was used, television receivers as well could dispense with a power transformer. The vapor is deposited on the inside of the glass envelope, leaving a silver-colored metallic patch that continues to absorb small amounts of gas that may leak into the tube during its working life. With the voltage of the grid less than that of the cathode, no direct current could pass from the cathode to the grid.