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Place of Origin: China Material: Stainless Steel Structure: Ball Brand Name: AOMI Certification: ISO9001 Terms of Payment: L/C at sight, T/T 30% deposit, balance paid after copy of B/L Minimum Order: 500pcs Delivery Lead Time: 30 days Features: 1) Sanitary stainless steel ball valve 2) Material quality: SUS304, SUS316L 3) Flux domination of pipeline: DN25-150 and 1′ - 6′ 4) Standards: ISO9001, DIN, SMS, IDF
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A valve RF amplifier (UK and Aus.) or tube amplifier (U.S.), is a device for electrically amplifying the power of an electrical signal, typically (but not exclusively) radio frequency signals.
Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers during the 1960s and 1970s, initially for receivers and low power stages of transmitters, transmitter output stages switching to transistors somewhat later. Specially constructed valves are still in use for very high power transmitters, although rarely in new designs.
Contents
1 Valve characteristics
1.1 Circuit advantages of valves
1.2 Disadvantages of valves
1.3 Distortion
2 Applications
2.1 Historic transmitters and receivers
2.2 Modern narrow band RF / tuned amplifiers
3 Radio circuits
3.1 Transmitter baseband anode circuits
3.2 Active (or tuned grid) amplifier
3.2.1 Operation
3.3 Passive grid amplifier
3.3.1 Advantages
3.3.2 Disadvantages
3.4 Grounded grid amplifier
3.4.1 Advantages
3.4.2 Disadvantages
3.5 Neutralization
3.6 Class C amplifiers
3.7 UHF
3.8 Tube noise and noise figure
4 Decline
5 Footnotes
6 References
7 External links
//
Valve characteristics
Valves are high voltage/low current devices in comparison with transistors (and especially MOSFETs) and their transfer characteristics show very flat anode current vs. anode voltage indicating high anode output impedances.
The high working voltage makes them 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 transformer is required. The transformer is a critical component and heavily influences the performance (and cost) of the amplifier.
Many power valves have good open-loop linearity, but only modest gain or transconductance. As a result, valve amplifiers usually need only modest levels of feedback. Signal amplifiers using tubes are capable of very high frequency response ranges - up to radio frequency. 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 high end.
Circuit advantages of valves
very linear (especially triodes) making it viable to use them in low distortion linear circuits with little or no negative feedback[citation needed]
extremely high input impedance (cf bipolar transistors but a characteristic shared by FETs)
Valves are high voltage devices and thus inherently suitable for very high voltage circuits.
Valves 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, and especially high power/high voltage applications such as Radio & TV transmitters long into the age when transistors had displaced valves in most other applications. However today these also are increasingly obsolete
Electrically very robust, they can tolerate overloads which would destroy bipolar transistor systems in milliseconds (of particular significance in military and other “strategically important” systems).
Disadvantages of valves
Cost
Heater supplies are required for the cathodes
Dangerously high voltages are required for the anodes
High impedance / low current output unsuitable for direct drive of many real world loads, notably various form of electric motor
Valves may have a shorter working life than solid state parts due to various failure mechanisms (cathode poisoning, breakages (ie open circuit) or shorts internally, notably of the heater or grid structures, or in the case of glass valves, physical breakage, although this should not be overstated: many valve types typically have operation lives of the tens of thousands of hours and an indefinite shelf life (many 60 year old tubes are still in regular use), and in worst case a failed tube can simply be unplugged and replaced by a user, cf a failed transistor which normally destroys the entire product beyond economic repair
Compared to transistors, valves have the disadvantage of being available in a single polarity only. In most processes transistors are available in complementary polarities (e.g., NPN/PNP), making possible many circuit configurations that cannot be realized with valves.
Distortion
Historic radio techniques were…(and so on)
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