Other vacuum tube devices

Many devices were built during the 1920–1960 period using vacuum-tube techniques. Most such tubes were rendered obsolete by semiconductors; some techniques for integrating multiple devices in a single module, sharing the same glass envelope have been discussed above, such as the Loewe 3NF. Vacuum-tube electronic devices still in common use include the magnetron, klystron, photomultiplier, x-ray tube, traveling-wave tube and cathode ray tube. The magnetron is the type of tube used in all microwave ovens. In spite of the advancing state of the art in power semiconductor technology, the vacuum tube still has reliability and cost advantages for high-frequency RF power generation. Photomultipliers are still the most sensitive detectors of light. Many televisions, oscilloscopes and computer monitors still use cathode ray tubes, though flat panel displays are becoming more popular as prices drop.

Many of the better tube radios had so-called "tuning eye" indicator tubes behind their front panels, with just the top of the tube showing. These tubes were used as a visual indication of received signal strength, and an aid to properly tuning in a station.

Secondary emission is the term for what happens when electrons in a vacuum strike certain materials, and the impacts cause electrons to be emitted. For some materials, more electrons are emitted than originally hit the surface. Such devices, called electron multipliers, amplify the current represented by the incoming electrons. Several stages (as many as 15 or so) can be cascaded for high gain, and are essential parts of very sensitive phototubes, usually called photomultipliers or multiplier photoubes. The image orthicon TV studio camera tubes also used multistage photomultipliers.

For decades, electron-tube designers tried to use secondary emission to obtain more amplification in vacuum tubes with hot cathodes, but they suffered from short life because the material used for the secondary-emission electrode (called a dynode) "poisoned" the tube's hot cathode. (For instance, the interesting RCA 1630 secondary-emission tube was marketed, but did not last.) However, eventually, Philips of The Netherlands developed the EFP60 tube that had a satisfactory lifetime, and was used in at least one product, a laboratory pulse generator. However, transistors were rapidly improving, and eclipsed tubes in general.

A variant, called a channel electron multiplier, is a curved tube, such as a helix, coated on the inside with material with good secondary emission. One type had a little funnel to capture incoming electrons. The tube was resistive, and its ends were connected to enough voltage to create repeated cascades of electrons.

Tektronix made a high-performance wideband oscilloscope CRT with a channel electron multiplier plate behind the phosphor layer. This plate was a bundled array of a huge number of short individual c.e.m. tubes that accepted a low-current beam and intensified it to provide a display of practical brightness. (The electron optics of the wideband electron gun could not provide enough current to directly excite the phosphor.)

The fluorescent displays commonly used on videocassette recorders, some microwave oven control panels, and automotive dashboards are vacuum tubes, using phosphor-coated anodes to form the display characters, and a heated filamentary cathode as an electron source. These are referred to as "VFDs", or vacuum fluorescent displays. Because the filaments are in view, they must be operated at temperatures where the filament does not glow visibly. Often found in automotive applications, their high brightness allows reading the display in daylight. VFD tubes are flat and rectangular, as well as relatively thin. Typical VFD phosphors emit a broad-spectrum greenish-white light, permitting use of color filters. This type of phosphor provides a bright glow with only modest operating voltage, low tens of volts.

Some tubes, such as magnetrons, traveling-wave tubes, carcinotrons, and klystrons, combine magnetic and electrostatic effects. These are efficient (usually narrow-band) RF producers and still find use in radar, microwave ovens and industrial heating. Traveling-wave tubes (TWTs) are very good amplifiers; they are used in some communications satellites. High-powered klystron amplifier tubes can provide hundreds of kilowatts in the UHF range.

Gyrotrons or vacuum masers, used to generate high-power millimetre band waves, are magnetic vacuum tubes in which a small relativistic effect, due to the high voltage, is used for bunching the electrons. Gyrotrons can generate very high powers (hundreds of kilowatts). Free electron lasers, used to generate high-power coherent light and perhaps even X rays, are highly relativistic vacuum tubes driven by high-energy particle accelerators.

Particle accelerators can be considered vacuum tubes that work backward, the electric fields driving the electrons, or other charged particles. In this respect, a cathode ray tube is a particle accelerator.

A tube in which electrons move through a vacuum (or gaseous medium) within a gas-tight envelope is generically called an electron tube.

Some condenser microphone designs use built-in vacuum tube preamplifiers.

Jolida JD502B, a modern tube integrated amplifier, with preamp tubes in front, power tubes in back.

As of 2008, scores of small companies are manufacturing audiophile amplifiers and preamps that use vacuum tubes.^[15]

Vacuum tubes using field electron emitters

In the early years of the 21st century there has been renewed interest in vacuum tubes, this time with the electron emitter formed on a flat silicon substrate, as in integrated circuit technology. This subject is now called Vacuum Nanoelectronics. The most common design uses a cold cathode in the form of a large-area field electron source (for example a field emitter array). With these devices, electrons are field-emitted from a large number of closely spaced individual emission sites.

Their claimed advantages include greatly enhanced robustness combined with the ability to provide high power outputs at low power consumptions. Operating on the same principles as traditional tubes, prototype device cathodes have been fabricated in several different ways. Although a common approach is to use a field emitter array, one interesting idea is to etch electrodes to form hinged flaps – similar to the technology used to create the microscopic mirrors used in Digital Light Processing) that are stood upright by an electrostatic charge.

Such integrated microtubes may find application in microwave devices including mobile phones, for Bluetooth and Wi-Fi transmission, in radar and for satellite communication. Presently they are being studied for possible applications in field emission display technology, but significant production problems seem to exist.

Modern manufacturers

Vacuum tubes are still being manufactured in the following countries:

China

Manufacturer	Area of expertise
Shuguang Electron Group Co.	Primarily audio tubes, also some rare transmitting models (211, 805, 807, 813, 845 and 6146B). Tubes marketed by Shuguang, Valve Art, TAD, Sophia Electric, Ruby Tubes and Taylor Tubes brand names.
Tianjin Quanerzhen Electron Tube Technology Co.	Very small manufacturer of high-end audio tubes. Products marketed by Full Music brand.
Nanjing Sanle Electronics Co.	Transmitting and industrial tubes. Some models (3-500ZG & 4-400C) marketed by Taylor Tubes brand.
JiangXi Jingguang Electronics Co.	Ceramic transmitting tubes, some of them marketed by Penta Laboratories.
Huaguang Electric Power & Electronics Co.	Transmitting and industrial tubes, also Chinese made 833C.

Russia

Manufacturer	Area of expertise
ZAO Ekspopul - New Sensor Inc.	Audio tube factory of New Sensor Inc.; Tubes are marketed as Sovtek, Electro Harmonix, Tung-Sol, Mullard, Genalex Gold Lion and also Svetlana S-marked in USA. Known formerly as tube factory of JSC Reflektor.
LLC "Ryazan" Vacuum Components	Russian made SV811 and SV572 series tubes for audio applications and transmitting tubes like 811A, 572B and GU-81, marketed in western countries by Svetlana, Sovtek and Ryazan brands
"SED-SPb" Svetlana Electron Devices, St.Petersburg - JSC Svetlana	Svetlana transmitting and "Winged-C" audio tubes
JSC "Voskhod" KRLZ	Tubes for small signal RF and audio applications
HC JSC NEVZ-Soyuz	Ceramic transmitting and microwave tubes, known as Novosibirsk Electro-Vacuum Plant - Soyuz

United States

Manufacturer	Area of expertise
Western Electric Inc.	300B triodes
Communications & Power Industries Inc.	Eimac and rebuilt Econco high power transmitting tubes
Burle Industries Inc.	Industrial and transmitting tubes, formerly factory of RCA
MPD Components Inc.	Planar triodes and magnetrons, formerly Ken-Rad and later GE tube factory
MU Incorporated	Contract manufacturer of obsolete electron tube models for special purposes.
LND Inc.	Geiger-Mueller tubes

United Kingdom

Manufacturer	Area of expertise
e2v Technologies Ltd.	Transmitting tubes, formerly known as English Electric Valve Co. Ltd.
Centronic Ltd.	Geiger-Mueller tubes, formerly Philips GM-tubes
TMD Technologies Ltd.	Magnetrons, Klystrons, Travelling Wave Tubes, Transmitters (formerly THORN Microwave Devices Ltd.)

Germany

Manufacturer	Area of expertise
Vacutec GmbH.	Geiger-Mueller tubes

France

Manufacturer	Area of expertise
Covimag	Transmitting tubes. Products marketed by Richardson Electronics with Amperex brand name. Formerly Philips transmitting tube factory.
Thales Electron Devices	High power transmitting tubes. Formerly known as Thomson-CSF.

Czech Republic

Manufacturer	Area of expertise
Emission Labs	High-end audio tubes
KR Audio Electronics s.r.o.	High-end audio tubes
Tesla Electrontubes s.r.o.	Transmitting tubes

Slovakia

Manufacturer	Area of expertise
JJ-Electronic	Primarily for audio applications, factory was formerly part of Tesla Electrontubes
Euro Audio Team	Very small manufacturer of high-end audio tubes, products marketed by EAT brand

Poland

Manufacturer	Area of expertise
Thales Lamina Przyrzady Elektronowe Sp.Z.o.o	Microwave tubes for radiolocation equipment, microwave tubes for industrial applications