Valve amplifier - AbsoluteAstronomy.com

A valve amplifier or tube amplifier is a type of electronic amplifier

Electronic amplifier

An electronic amplifier is a device for increasing the power of a signal.It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude...

that makes use of vacuum tubes to increase the power

Power (physics)

In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...

and/or amplitude

Amplitude

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation...

of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state

Solid state (electronics)

Solid-state electronics are those circuits or devices built entirely from solid materials and in which the electrons, or other charge carriers, are confined entirely within the solid material...

amplifiers during the 1960s and 1970s. Valve amplifiers are used for applications such as guitar amplifier

Guitar amplifier

A guitar amplifier is an electronic amplifier designed to make the signal of an electric or acoustic guitar louder so that it will produce sound through a loudspeaker...

s, satellite

Satellite

In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

transponder

Transponder

In telecommunication, the term transponder has the following meanings:...

s such as DirecTV

DirecTV

DirecTV is an American direct broadcast satellite service provider and broadcaster based in El Segundo, California. Its satellite service, launched on June 17, 1994, transmits digital satellite television and audio to households in the United States, Latin America, and the Anglophone Caribbean. ...

and GPS, audiophile stereo amplifiers, military applications (such as radar

Radar

Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

) and very high power radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

and UHF television

Television

Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

transmitter

Transmitter

In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...

Origins

Until the invention of the transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

in 1947, all practical amplifiers were made using thermionic valves. The simplest valve was invented by John Ambrose Fleming

John Ambrose Fleming

Sir John Ambrose Fleming was an English electrical engineer and physicist. He is known for inventing the first thermionic valve or vacuum tube, the diode, then called the kenotron in 1904. He is also famous for the left hand rule...

while working for the Marconi Company

Marconi Company

The Marconi Company Ltd. was founded by Guglielmo Marconi in 1897 as The Wireless Telegraph & Signal Company...

in London in 1904 and named the diode

Diode

In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...

, as it had two electrodes. The diode conducted electricity

Electricity

Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

in one direction only and was used as a radio detector and a rectifier

Rectifier

A rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...

.

In 1906 Lee De Forest

Lee De Forest

Lee De Forest was an American inventor with over 180 patents to his credit. De Forest invented the Audion, a vacuum tube that takes relatively weak electrical signals and amplifies them. De Forest is one of the fathers of the "electronic age", as the Audion helped to usher in the widespread use...

added a third electrode and invented the first electronic amplifying device, the triode

Triode

A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...

, which he named the Audion
Audion
An Audion is a wireless signal detector device invented by Lee De Forest in 1906.Audion may also refer to:* Audion , an electronic music album by Larry Fast* Audion , a media player for Apple Macintosh created by Panic...

. This additional control grid modulates the current that flows between cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

and anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

. The relationship between current flow and plate and grid voltage is often represented as a series of "characteristic curves" on a diagram. Depending on the other components in the circuit this modulated current flow can be used to provide current or voltage gain

Gain

In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...

.

The first application of valve amplification was in the regeneration of long distance telephony signals. Later, valve amplification was applied to the 'wireless' market that began in the early thirties. In due course amplifiers for music and later television were also built using valves.
The overwhelmingly dominant circuit topology during this period was the single-ended triode

Single-ended triode

A single-ended triode vacuum tube electronic amplifier uses a single triode to produce an output, in contrast to a push-pull amplifier which uses a pair of devices with antiphase inputs to generate an output with the wanted signals added and the distortion components subtracted...

gain stage, operating in class A, which gave very good sound (and reasonable measured distortion performance) despite extremely simple circuitry with very few components: important at a time when components were hand made and extremely expensive. Before World War II, almost all valve amplifiers were of low gain and with linearity dependent entirely on the inherent linearity of the valve itself, typically 5% distortion at full power.

Negative feedback

Negative feedback

Negative feedback occurs when the output of a system acts to oppose changes to the input of the system, with the result that the changes are attenuated. If the overall feedback of the system is negative, then the system will tend to be stable.- Overview :...

(NFB) was invented by Harold Stephen Black

Harold Stephen Black

Harold Stephen Black was an American electrical engineer, who revolutionized the field of applied electronics by inventing the negative feedback amplifier in 1927. To some, his invention is considered the most important breakthrough of the twentieth century in the field of electronics, since it...

in 1927, but initially little used since at that time gain

Gain

was at a premium. This technique allows amplifiers to trade gain for reduced distortion levels (and also gave other benefits such as reduced output impedance). The introduction of the Williamson amplifier

Williamson amplifier

A Williamson amplifier refers to a type of vacuum tube amplifier whose circuit design is similar to that originally published by D.T.N. Williamson.- Explanation :...

in 1947, which was extremely advanced in many respects including very successful use of NFB, was a turning point in audio power amplifier design, operating a push-pull output circuit in class AB1 to give performance surpassing its contemporaries.

Post-war developments

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

stimulated dramatic technical progress and industrial scale production economies. Increasing affluence after the war brought about for the first time a substantial and expanding consumer market. This enabled more advanced valve designs to be marketed at affordable prices, with the result that the 1960s saw the increasing spread of electronic gramophone players, and ultimately the beginnings of "high fidelity

High fidelity

High fidelity—or hi-fi—reproduction is a term used by home stereo listeners and home audio enthusiasts to refer to high-quality reproduction of sound or images, to distinguish it from the poorer quality sound produced by inexpensive audio equipment...

". Hifi was able to drive full frequency range loudspeakers (for the first time often with multiple drivers for different frequency bands) to significant volume levels. This combined with the spread of TV, produced a 'golden age' in valve development and also in the development of the design of valve amplifier circuits.

A range of topologies with only minor variations (notably different phase splitter

Phase splitter

A phase splitter is a device that separates a signal into multiple phases .The term is most often applied to amplifiers that produce two "balanced" voltage outputs: of equal amplitude but opposite polarity , but sometimes is used to refer to the generation of quadrature signals...

arrangements and the "Ultra-Linear

Ultra-Linear

Ultra-linear is a term used to describe a type of electronic circuit that is used to couple a tetrode or pentode vacuum-tube to a load ....

" transformer connection for tetrodes) rapidly became widespread. This family of designs remains the dominant high power amplifier topology to this day for music application. This period also saw continued growth in civilian radio, with valves being used for both transmitters and receivers.

Decline

From the 1970s the silicon transistor became increasingly pervasive. Valve production was sharply decreased, with the notable exception of cathode ray tube

Cathode ray tube

The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...

s (CRTs), and a reduced range of valves for amplifier applications. Popular low power tubes were dual triodes (ECCnn, 12Ax7 series) plus the EF86 pentode, and power valves were mostly being beam tetrode and pentodes (EL84, EL34, KT88 / 6550, 6L6), in both cases with indirect heating. This reduced set of types remains the core of valve production today.

The Soviets retained valves to a much greater extent than the West during the Cold War, for the majority of their communications and military amplification requirements, in part due to valves' ability to withstand instantaneous overloads (notably due to a nuclear detonation

Electromagnetic pulse

An electromagnetic pulse is a burst of electromagnetic radiation. The abrupt pulse of electromagnetic radiation usually results from certain types of high energy explosions, especially a nuclear explosion, or from a suddenly fluctuating magnetic field...

) that would destroy a transistor .

The dramatic reduction in size, power consumption, reduced distortion levels and above all cost of electronics products based on transistors has made valves obsolete for mainstream products since the 1970s. Valves remained in certain applications such as high power RF transmitters and the microwave oven

Microwave oven

A microwave oven is a kitchen appliance that heats food by dielectric heating, using microwave radiation to heat polarized molecules within the food...

, and audio amplification equipment, particularly for the electric guitar, recording studios, and high-end home stereos.

Audio Usage

In audio applications, valves continue to be highly desired by most professional users, particularly in recording studios' equipment and guitar amplifiers. Among stereo enthusiasts, there is a subgroup of audio buffs who advocate the use of tube amplifiers for home listening; they argue that tube amplifiers produce a "warmer" or more "natural" valve sound. Companies in Asia and Eastern Europe continue to produce valves to cater to this market.

Many professional guitar players use 'tube amps' because of their renown 'tone'. 'Tone' in this usage is referring to timbre, or pitch color, and can be a very subjective quality to quantify. Most audio technicians and scientists theorize that the 'even harmonic distortion' produced by valve tubes sounds more pleasing to the ear than transistors, regardless of style. Many of the musicians who use solid state amplification technology do so for its portability, low cost and high reliability, not its 'tone'. It is the tonal characteristics of valve tubes that have sustained them as the industry standard for guitars and studio microphone pre-amplification.

Tube amplifiers respond differently from transistor amplifiers when signal levels approach and reach the point of clipping

Clipping (audio)

Clipping is a form of waveform distortion that occurs when an amplifier is overdriven and attempts to deliver an output voltage or current beyond its maximum capability...

. In a tube amplifier, the transition from linear amplification to limiting is less abrupt than in a solid state unit, resulting in a less grating form of distortion at the onset of clipping. For this reason, some guitarists prefer the sound of an all-tube amplifier; the aesthetic properties of tube versus solid state amps, though, are a topic of debate in the guitarist community.

Characteristics

Valves are high voltage and low current devices in contrast to transistor

Transistor

s, which typically operate at lower voltages and higher currents for the same power level. The high working voltage makes valves well suited for radio transmitters, for example, and valves remain in use today for very high power radio transmitters, where there is still no other technology available. However, for most applications requiring an appreciable output current, a matching

Matching

In the mathematical discipline of graph theory, a matching or independent edge set in a graph is a set of edges without common vertices. It may also be an entire graph consisting of edges without common vertices.- Definition :...

transformer

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

is required. The transformer is a critical component and heavily influences the performance (and cost) of the amplifier.

Many power valves have good linearity but modest gain

Gain

or transconductance

Transconductance

Transconductance, also known as mutual conductance, is a property of certain electronic components. Conductance is the reciprocal of resistance; transconductance, meanwhile, is the ratio of the current change at the output port to the voltage change at the input port. It is written as gm...

. Signal amplifiers using tubes are capable of very high frequency response ranges – up to radio frequency

Radio frequency

Radio frequency is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals...

. Indeed, many of the directly heated single-ended triode (DH-SET) audio amplifiers are in fact radio transmitting tubes designed to operate in the megahertz range. In practice, however, tube amplifier designs typically "couple" stages either capacitively, limiting bandwidth at the low end, or inductively with transformers, limiting the bandwidth at both ends.

Advantages

Very linear (especially triodes) making it viable to use them in low distortion linear circuits with little or no negative feedback.
Inherently suitable for high voltage circuits.
Can be constructed on a scale that can dissipate large amounts of heat (some extreme devices even being water cooled). For this reason valves remained the only viable technology for very high power applications such as radio and TV transmitters long into the age when transistors had displaced valves in most other applications.
Very low "drift" (of specifications) over a wide range of operating conditions, specifically high heat and high power. Semiconductors are very heat sensitive by comparison, forcing compromises in solid state amplifier designs.
Electrically very robust, they can tolerate overloads for minutes which would destroy bipolar transistor
Bipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...

systems in millisecond
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....

s.
Easily removable for testing or replacement – it is much harder to replace a faulty transistor.
Softer clipping when overloading the circuit, which many audiophiles and musicians think gives a more pleasant sound.
Valves with the same type number tend to have very similar characteristics to each other whereas semiconductor devices of the same type can have considerably different characteristics.

Disadvantages

A cathode heater is required. Heater power represents a significant heat loss and energy use.
Higher voltages are required for the anodes, compared to solid state amplifiers of similar power rating.
They are significantly larger than equivalent solid-state devices
High impedance and low current output is unsuitable for direct drive of many real world loads, notably various forms of electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...

s.
Valves may have a shorter working life than solid state parts due to various failure mechanisms (such as heat, cathode poisoning, breakage, or internal short-circuits).
Available in a single polarity only whereas transistors are available in complementary polarities (e.g., NPN/PNP), making possible many circuit configurations that cannot be realized directly with valves.
Valve circuits must avoid introduction of noise from ac heater supplies.
Microphonics
Microphonics
Microphonics describes the phenomenon where certain components in electronic devices transform mechanical vibrations into an undesired electrical signal...

– valves may sometimes be sensitive to sound or vibration, inadvertently acting like a microphone
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

.
Power consumption due to the heater requirements.
During the life of a valve, its characteristics can change considerably as it ages whereas the characteristics of a semiconductor tend to change very little.

Operation

All amplifier circuits are classified by "class of operation" as A, B, AB and C etc. See amplifier classes. Some significantly different circuit topologies exist compared to transistor designs.

The grid (where the input signal is presented) needs to be biased substantially negative with respect to the cathode This makes it extremely difficult to direct couple the output of one valve to the input of a following valve as is normally done in transistor designs.

Valve stages are coupled with components rated to withstand several hundred volts, typically a capacitor, occasionally a coupling transformer. The phase shifts introduced by coupling networks can become problematic in circuits that have feedback.

There is no valve analog of the complementary devices widely used in "totem pole" output stages of silicon circuits. Push-pull valve topologies therefore typically require a transformer.

The very high output impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...

of valves (compared with transistors) usually requires matching transformers to drive low impedance loads such as loudspeakers or cutting lathe heads. The transformer is used as the load, in place of the resistor usually used in small-signal and driver stages. The impedance of the transformer primary at the frequencies in use is much higher than the DC resistance of the windings, often kilohms. High performance transformers are however severe engineering compromises, are expensive, and in operation are far from ideal. Transformers dramatically increase the cost of a valve amplifier circuit compared to a direct-coupled transistor alternative.

The open loop linearity of valves, especially triodes, makes it possible to use little or no negative feedback in circuits whilst retaining acceptable or even excellent distortion performance (especially for small-signal circuits).

Topologies

Linear small signal circuits almost invariably use a triode in the single ended gain stage topology (in class A), including the output stage.
Broadband valve amplifiers typically use class A1 or AB1.
Modern high power output stages are usually push pull, often necessitating some form of phase splitter to derive a differential/balanced drive signal from a single ended input, typically followed by a further gain stage (the "driver") prior to the output tubes. For example SRPP)
single ended power stages using very large valves exist and dominate in radio transmitter applications. A sidebar is the observation that the niche "DH-SET" topology favored by some audiophiles are extremely simple and typically constructed using valve types originally designed for use in radio transmitters
more complex topologies (notably the use of active loads) can improve linearity and frequency response (by removing Miller capacitance effects).

Output impedance

The high output impedance of tube plate circuits is not well matched to low-impedance loads such as loudspeakers or antennas. A matching network is required for efficient power transfer; this may be a transformer at audio frequencies, or various tuned networks at radio frequencies.

Audio Frequency (AF) and Broadband amplifiers

Valves remain in widespread use in guitar and high-end audio

High-end audio

High-end audio is a term used to describe a class of consumer home audio equipment marketed to audio enthusiasts on the basis of high price or quality, and esoteric or novel sound reproduction technologies. High-end audio can refer simply to the price, to the build quality of the components, or to...

amplifiers due to the sound quality they produce, due to their linear nature resulting in low distortion. They are largely obsolete elsewhere because of higher power consumption, costs, reliability, and weight in comparison to transistors.

Telephony

Telephony was the original, and for many years was a driving application for audio amplification. A specific issue for the telecommunication industry was the technique of multiplexing many (up to a thousand) voice lines onto a single cable, at different frequencies.

The advantage of this is that a single valve "repeater" amplifier can amplify many calls at once, this being very cost effective. The problem is that the amplifiers need to be extremely linear, otherwise "intermodulation

Intermodulation

Intermodulation or intermodulation distortion is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities...

distortion" (IMD) will result in "crosstalk" between the multiplexed channels. This stimulated development emphasis towards low distortion far beyond the nominal needs of a single voice channel.

Audio

Today the main application for valves is audio amplifiers for high-end hi-fi and musical performance use with electric guitar

Electric guitar

An electric guitar is a guitar that uses the principle of direct electromagnetic induction to convert vibrations of its metal strings into electric audio signals. The signal generated by an electric guitar is too weak to drive a loudspeaker, so it is amplified before sending it to a loudspeaker...

s, electric bass

Electric Bass

Electric bass can mean:*Electric upright bass, the electric version of a double bass*Electric bass guitar*Bass synthesizer*Big Mouth Billy Bass, a battery-powered singing fish...

es, and Hammond organ

Hammond organ

The Hammond organ is an electric organ invented by Laurens Hammond in 1934 and manufactured by the Hammond Organ Company. While the Hammond organ was originally sold to churches as a lower-cost alternative to the wind-driven pipe organ, in the 1960s and 1970s it became a standard keyboard...

s, although these applications have different requirements regarding distortion which result in different design compromises, although the same basic design techniques are generic and widely applicable to all broadband amplification applications, not only audio.

Post World War II, the majority of valve power amplifiers are of the Class AB-1 "push pull" ultralinear topology, or lower cost single ended i.e. 6BQ5/EL84 power tubes, but niche products using the DH-SET and even OTL topologies still exist in small numbers.

Instrumentation amplifiers

The basic moving coil voltmeter and ammeter itself takes a small current and thus loads the circuit to which it is attached. This can significantly alter the operating conditions in the circuit being measured. The vacuum tube voltmeter (VTVM) uses the high input impedance of a valve to buffer the circuit being measured from the load of the ammeter.

Valve oscilloscopes share this very high input impedance and thus can be used to measure voltages even in very high impedance circuits. There may typically be 3 or 4 stages of amplification per display channel. In later oscilloscopes, a type of amplifier using a series of tubes connected at equal distances along transmission line

Transmission line

In communications and electronic engineering, a transmission line is a specialized cable designed to carry alternating current of radio frequency, that is, currents with a frequency high enough that its wave nature must be taken into account...

s, known as a distributed amplifier

Distributed Amplifier

Distributed amplifiers are circuit designs that incorporate transmission line theory into traditional amplifier design to obtain a larger gain-bandwidth product than is realizable by conventional circuits.-History:...

was employed to amplify very high frequency vertical signals before application to the display tube. Valve oscilloscopes are now obsolete.

In the closing years of the valve era, valves were even used to make "operational amplifiers" – the building blocks of much modern linear electronics. An op-amp typically has a differential input stage and a totem pole output, the circuit usually having a minimum of five active devices. A number of "packages" were produced that integrated such circuits (typically using two or more glass envelopes) into a single module that could be plugged into a larger circuit (such as an analog computer). Such valve op-amps were very far from ideal and quickly became obsolete, being replaced with solid-state types.

Narrow band and radio frequency tuned amplifiers

Historically (pre-WWII) "transmitting tubes" were among the most powerful tubes available. These usually had directly heated thoriated filaments cathodes that glowed like light bulbs. Some tubes were capable of being driven so hard that the anode would itself glow cherry red; the anodes were machined from solid material (rather than fabricated from thin sheet) to withstand heat without distorting. Notable tubes of this type are the 845 and 211. Later tetrodes and pentodes such as 817 and (direct heated) 813 were also used in large numbers in (especially military) radio transmitters

RF circuits are significantly different from broadband amplifier circuits. The antenna or following circuit stage typically contains one or more adjustable capacitive or inductive component allowing the resonance of the stage to be accurately matched with carrier frequency in use, to optimize power transfer from and loading on the valve, a so called "tuned circuit".

Broadband circuits require flat response over a wide range of frequencies. RF circuits by contrast are typically required to operate at high frequencies but often over a very narrow frequency range. For example, an RF device might be required to operate over the range 144 to 146 MHz (just 1.4%)

Today, radio transmitters are overwhelmingly silicon based, even at microwave frequencies. However an ever decreasing minority of high power radio frequency amplifiers continue to have valve construction.

External links

Tubeopedia – Wiki of electronic tubes and related topics
The Vacuum Tube FAQ – Henry Pasternack's FAQ from rec.audio
The Audio Circuit – An almost complete list of manufacturers, DIY kits, materials and parts and 'how they work' sections on valve amplifiers
Conversion calculator – distortion factor to distortion attenuation and THD
AX84.com – Although oriented towards valve guitar amplifiers, AX84's free schematics and theory document apply well to any tube/valve project
http://sites.google.com/site/diyrbt7 - A high performance phase splitter with sheet beam tube.
Tube Data Archive – Massive collection (7 GB+) of tube data sheets and information.

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Origins

Post-war developments

Decline

Audio Usage

Characteristics

Advantages

Disadvantages

Operation

Topologies

Output impedance

Audio Frequency (AF) and Broadband amplifiers

Telephony

Audio

Instrumentation amplifiers

Narrow band and radio frequency tuned amplifiers

See also

External links