A triode is an electronic amplifying vacuum tube consisting of three electrodes inside an evacuated glass envelope: a heated filament or cathode, a grid, and a plate (anode). Developed from Lee De Forest's 1906 Audion, a partial vacuum tube that added a grid electrode to the thermionic diode, the triode was the first practical electronic amplifier and the ancestor of other types of vacuum tubes such as the tetrode and pentode. Its invention helped make amplified radio technology and long-distance telephony possible. Triodes were widely used in consumer electronics devices such as radios and televisions until the 1970s, when transistors replaced them. Today, their main remaining use is in high-power RF amplifiers in radio transmitters and industrial RF heating devices. In recent years there has been a resurgence in demand for low power triodes due to renewed interest in tube-type audio systems by audiophiles who prefer the sound of tube-based electronics.
A vacuum tube, electron tube, valve, or tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.
A tetrode is a vacuum tube having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids, and a plate. There are several varieties of tetrodes, the most common being the screen-grid tube and the beam tetrode. In screen-grid tubes and beam tetrodes, the first grid is the control grid and the second grid is the screen grid. In other tetrodes one of the grids is a control grid, while the other may have a variety of functions.
The control grid is an electrode used in amplifying thermionic valves such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the anode (plate) electrode. The control grid usually consists of a cylindrical screen or helix of fine wire surrounding the cathode, and is surrounded in turn by the anode. The control grid was invented by Lee De Forest, who in 1906 added a grid to the Fleming valve to create the first amplifying vacuum tube, the Audion (triode).
A suppressor grid is a wire screen used in a thermionic valve to suppress secondary emission. It is also called the antidynatron grid, as it reduces or prevents dynatron oscillations. It is located between the screen grid and the plate electrode (anode). The suppressor grid is used in the pentode vacuum tube, so called because it has five concentric electrodes: cathode, control grid, screen grid, suppressor grid, and plate, and also in other tubes with more grids, such as the hexode. The suppressor grid and pentode tube were invented in 1926 by Gilles Holst and Bernard D. H. Tellegen at Phillips Electronics.
In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a process called secondary emission. It was the first negative resistance vacuum tube oscillator. The dynatron oscillator circuit was used to a limited extent as beat frequency oscillators (BFOs), and local oscillators in vacuum tube radio receivers as well as in scientific and test equipment from the 1920s to the 1940s but became obsolete around World War 2 due to the variability of secondary emission in tubes.
KT66 is the designator for a beam power tube introduced by Marconi-Osram Valve Co. Ltd. (M-OV) of Britain in 1937 and marketed for application as a power amplifier for audio frequencies and driver for radio frequencies. The KT66 is a beam tetrode that utilizes partially collimated electron beams to form a low potential space charge region between the anode and screen grid to return anode secondary emission electrons to the anode and offers significant performance improvements over comparable power pentodes. In the 21st century, the KT66 is manufactured and used in some high fidelity audio amplifiers and musical instrument amplifiers.
A beam tetrode, sometimes called a beam power tube, is a type of vacuum tube or thermionic valve that has two grids and forms the electron stream from the cathode into multiple partially collimated beams to produce a low potential space charge region between the anode and screen grid to return anode secondary emission electrons to the anode when the anode potential is less than that of the screen grid. Beam tetrodes are usually used for power amplification, from audio frequency to radio frequency. The beam tetrode produces greater output power than a triode or pentode with the same anode supply voltage. The first beam tetrode marketed was the Marconi N40, introduced in 1935. Beam tetrodes manufactured and used in the 21st century include the 4CX250B, KT66 and variants of the 6L6.
The 6V6 is a beam-power tetrode vacuum tube. The first of this family of tubes to be introduced was the 6V6G by Ken-Rad Tube & Lamp Corporation in late 1936, with the availability by December of both Ken-Rad and Raytheon 6V6G tubes announced. It is still in use in audio applications, especially electric guitar amplifiers.
A pentode is an electronic device having five electrodes. The term most commonly applies to a three-grid amplifying vacuum tube or thermionic valve that was invented by Gilles Holst and Bernhard D.H. Tellegen in 1926. The pentode was developed from the screen-grid tube or shield-grid tube by the addition of a grid between the screen grid and the plate. The screen-grid tube was limited in performance as an amplifier due to secondary emission of electrons from the plate. The additional grid is called the suppressor grid. The suppressor grid is usually operated at or near the potential of the cathode and prevents secondary emission electrons from the plate from reaching the screen grid. The addition of the suppressor grid permits much greater output signal amplitude to be obtained from the plate of the pentode in amplifier operation than from the plate of the screen-grid tube at the same plate supply voltage. Pentodes were widely manufactured and used in electronic equipment until the 1960s to 1970s, during which time transistors replaced tubes in new designs. During the first quarter of the 21st century, a few pentode tubes have been in production for high power radio frequency applications, musical instrument amplifiers, home audio and niche markets.
A grid leak detector is an electronic circuit that demodulates an amplitude modulated alternating current and amplifies the recovered modulating voltage. The circuit utilizes the non-linear cathode to control grid conduction characteristic and the amplification factor of a vacuum tube. Invented by Lee De Forest around 1912, it was used as the detector (demodulator) in the first vacuum tube radio receivers until the 1930s.
The EL34 is a thermionic vacuum tube of the power pentode type. The EL34 was introduced in 1955 by Mullard, who were owned by Philips. The EL34 has an octal base and is found mainly in the final output stages of audio amplification circuits; it was also designed to be suitable as a series regulator by virtue of its high permissible voltage between heater and cathode and other parameters. The American RETMA tube designation number for this tube is 6CA7. The USSR analog was 6P27S.
In Europe, the principal method of numbering vacuum tubes was the nomenclature used by the Philips company and its subsidiaries Mullard in the UK, Valvo(de, it) in Germany, Radiotechnique (Miniwatt-Dario brand) in France, and Amperex in the United States, from 1934 on. Adhering manufacturers include AEG (de), CdL (1921, French Mazda brand), CIFTE (fr, Mazda-Belvu brand), EdiSwan (British Mazda brand), Lorenz (de), MBLE(fr, nl), RCA (us), RFT(de, sv) (de), Siemens (de), Telefunken (de), Tesla (cz), Toshiba (ja), Tungsram (hu), and Unitra. This system allocated meaningful codes to tubes based on their function and became the starting point for the Pro Electron naming scheme for active devices.
Vacuum tubes produced in the former Soviet Union and in present-day Russia carry their own unique designations. Some confusion has been created in "translating" these designations, as they use Cyrillic rather than Latin characters.
The KT88 is a beam tetrode/kinkless tetrode vacuum tube for audio amplification.
Ultra-linear electronic circuits are those used to couple a tetrode or pentode vacuum-tube to a load.
Explosive forming is a metalworking technique in which an explosive charge is used instead of a punch or press. It can be used on materials for which a press setup would be prohibitively large or require an unreasonably high pressure, and is generally much cheaper than building a large enough and sufficiently high-pressure press; on the other hand, it is unavoidably an individual job production process, producing one product at a time and with a long setup time. There are various approaches; one is to place metal plate over a die, with the intervening space evacuated by a vacuum pump, place the whole assembly underwater, and detonate a charge at an appropriate distance from the plate. For complicated shapes, a segmented die can be used to produce in a single operation a shape that would require many manufacturing steps, or to be manufactured in parts and welded together with an accompanying loss of strength at the welds. There is often some degree of work hardening from the explosive-forming process, particularly in mild steel.
The 807 is a beam tetrode vacuum tube, widely used in audio- and radio-frequency power amplifier applications.
