312:, driving the signal far outside the linear range of the tube circuit, to deliberately generate large amounts of harmonic distortion. The distortion and overdrive characteristics of valves are quite different from transistors (not least the amount of voltage headroom available in a typical circuit) and this results in a distinctive sound. Amplifiers for such performance applications typically retain tone and filter circuits that have largely disappeared from modern hi-fi products. Amplifiers for guitars in particular may also include a number of "effects" functions.
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the anode current from becoming too small and ensuring that grid current does not flow at any point. In this case, distortion is largely relatively unobjectionable second harmonic, with percentage closely proportional to the output amplitude. Adding modest negative feedback improves linearity further. Pentodes of the same power dissipation are capable of higher output power than triodes, but distortion is higher and more objectionable.
73:
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relatively undersized power supply capacitors producing a characteristic "sag" at instants of peak output and power draw, and subsequent recovery, that is often considered musically engaging. In addition, guitarists may employ acoustic feedback, further modifying the resulting sound (noting that the feedback signal has a slight time lag relative to the original signal).
530:
631:). Mains hum from the heater filaments is a potential problem in low-level valve stages. Modern amplifiers invariably run from the mains; as there is little need to minimise costs in expensive valve amplifiers, the heater supply is often rectified and even regulated to reduce hum to an absolute minimum.
466:
Prior to WWII, almost all electronic amplifiers were triodes used without feedback. The inherent, albeit imperfect, linearity of tubes makes it possible to get acceptable distortion performance without correction. Amplitude distortion in a class A triode stage can be small if care is taken to prevent
598:
radios. Transistors had the major advantage of working off the voltage provided by a car battery. Early radios required a power unit to convert the battery voltage to a value high enough for the valves. Later radios used special valves that were designed to operate directly from a 12 volt supply.
649:
Amplifiers from and prior to this period often have a distinctive sound that today is still widely referred to as "valve sound" and "warm". This tone is not strictly caused by the use of valves rather than transistors; it is merely a sound that was originally associated with amplifiers built using
356:
Guitar amplifiers are often designed so they can, when desired by the guitarist, distort and create a tone rich in harmonics and overtones. The characteristics of the tube and the circuit directly influence the nature of the sound produced. Even the power supply can influence the tonal shape, with
634:
A representative valve preamp from the 1950s is the Leak 'varislope' series of preamps, which included a switchable rumble filter, a switchable scratch filter with selectable slopes and corner frequency, continuously variable treble and bass tone controls and a selection of 4 different gramophone
360:
Guitar amplifiers are typically designed to withstand a lot of abuse both electrically and physically (since guitarists often travel to gigs, etc.) In large systems the amplifier is separate from the speaker enclosure(s), but in smaller systems it is often integrated, forming a so-called "combo".
462:
riode circuit. Power output ranged from a few watts to perhaps 20 watts for an exceptionally powerful amplifier (modern semiconductor amplifiers produce much higher power). Today this type of circuit retains a niche following at the very extreme of audiophile hi-fi, where it is often referred as
304:
Valve amplifiers for guitars (and to a lesser degree vocals and other applications) have different purposes from those of hi-fi amplifiers. The purpose is not necessarily to reproduce sound as accurately as possible, but rather to fulfill the musician's concept of what the sound should be. For
599:
These later radios were hybrid designs which used transistors only for the audio output stages because a 12 volt power amplifier valve was not practical. For this and other applications, transistors are smaller, cheaper, more durable, use less power, run cooler, and do not need to warm up.
552:, represent the pinnacle of the technology and of production quality. Valve amplifiers produced since that time usually use one of these tubes, which have remained in continuous production (apart from KT66) ever since. Output power was typically 20 watts, exceptionally 35W.
435:'. Cinema sound systems of this period were predominantly supplied by "Westrex", related to the Western Electric company, a telecoms supplier, who were also the makers of the 300B DHT tube that today is central to current production DH-SET
611:
Due to the very poor technical performance of early gramophones, the lack of standardised equalisations, poor components and accessories (including loudspeakers), preamplifiers historically contained extensive and very flexible
390:
connection. The output stage is preceded by a voltage amplification stage (pentode or twin triode) and a phase-splitter (twin triode). Twin triodes with two identical sections in one envelope are used, usually the noval types
602:
Some enthusiasts prefer "tube amps", so a small number of valve car stereos are still made. Manufacturers include
Milbert Amplifiers, Blade, Manley, and Sear Sound. Some are hybrid designs with transistors and valves.
519:
Manufacturers bringing high-quality domestic hi-fi to a steadily widening audience, eventually leading to Dynaco selling over 300,000 ST-70's, making it the world's most popular hi-fi amplifier of any type to
663:
the use of very large amounts of feedback in signal transformerless semiconductor circuits, which leads to distortion that is small but has a much larger proportion of high harmonics than in valve circuits.
352:
Rear view of a valve combo guitar amplifier. Visible are two glass 6L6 output tubes, six smaller 12AX7 preamp tubes in their metal tube retainers and both the power transformer and the output transformer.
344:
were probably audio amplifiers made for other purposes and pressed into service, but the electric guitar and its amplification quickly developed a life of its own, supported by specialist manufacturers.
676:
under-dimensioned and unregulated power supplies in amplifiers where power drawn varied significantly with instantaneous power output (class A not affected, classes AB1, AB2, B, increasingly so),
537:
Valve amplification peaked as the mainstream technology during the 1960s and 70s, with device and circuits being highly developed. There have been only minor refinements since then.
657:
simple circuits with relatively little feedback, producing mainly low-harmonic distortion (feedback that could be applied was limited by phase shift in the output transformer);
508:
output stage (a tapped push-pull output transformer providing power intermediate between triodes and pentodes, at lower distortion than either) was originated by
424:. Radio applications followed soon after, where valves were used for both the audio (AF) and radio (RF) circuitry. (RF is outside the scope of this article, see
486:
Widespread adoption of push pull allowed smaller (and thus cheaper) transformers, combined with more power (typically 10 to 20 watts) to handle peaks. The
420:
The earliest mass usage of valve audio amplifiers was for telephony. Valve amplifiers were critical in development of long-distance telephone circuits and
361:
Since the amplifier is usually at the top of the combo, the tubes often hang upside down facing the body of the enclosure. They may be held in with clips.
305:
example, distortion is almost universally considered undesirable in hi-fi amplifiers but may be considered a desirable characteristic in performance.
431:
Among the first applications of sound recording and electronic replay around the 1920s was its use in many cinemas equipping for exhibiting the new '
702:
In addition to a range of commodity valve amplifiers, some amplifiers were made which are still highly regarded today. Among the best known are:
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amplifiers. While solid-state devices prevail in most audio amplifiers today, valve audio amplifiers are still used where their
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937:– An almost complete list of manufacturers, DIY kits, materials and parts and 'how they work' sections on valve amplifiers.
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circuit. This design and the
Williamson were widely implemented and imitated, with or without crediting the originator.
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valves simply because that is what was available at the time. The origins of that particular sound are in part due to:
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Most modern valve guitar amplifiers use a class AB1 push-pull circuit with a pair of power pentodes or beam tetrodes,
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and Keroes in the USA in 1951, and became the dominant topology during the post war recovery of consumer products
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in the push pull topology yielded greater power and linearity, notably following the publication in 1947 of the
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power pentode was widely used in less expensive 10-watt ultralinear power amplifiers, still of high fidelity.
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Conceptual diagram of a poweramplifier with a split-load phase inverter and push-pull EL34 pentodes endstage
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Small signal valves overwhelmingly changed from octal base tubes, notably the audio tube of choice, the
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The electric guitar originates from
Rickenbacker in the 1930s but its modern form was popularised by
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918:. A long running journal devoted to tube amp construction, published by the Audio Amateur (TAA) Corp
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891:– Contains a short introduction, the rest of the book is many photographs of some tube amplifiers.
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Commercial tube manufacturers developed designs based on their own products, most notably the
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Various basic circuits have been used in designs and in various approaches to construction.
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dedicated guitar amplifiers had frequency response and distortion suited to their purpose,
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are considered pleasing, for example in music performance or music reproduction.
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Factors relevant to valve equipment not designed to high-fidelity standards:
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483:, which set the standard (and the dominant topology) for what was to follow.
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This article is about audio tube amps. For amps from the Valve company, see
931:– Free schematic archive of vintage guitar amplifier and effect schematics.
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the typical circuit designs of the time (class A or AB1), combined with
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Small signal circuits are often deliberately designed to have very high
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571:(UK, in the US known as 12AX7,12AT7, etc.). The lower-power noval base
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in 1937 in the UK, but popularised following publication of a paper by
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the introduction of the "Point One" series of amplifiers (in 1945) by
867:– Compendium of articles of historic interest to people in this field
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912:(A detailed discussion of the limitations of NFB as a panacea)
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in the UK, which first set a performance standard of 0.1% THD
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of the amplifier and so the sound produced by the system.
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Valve preamplifiers use triodes or low-noise pentodes (
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poor quality output transformers in budget equipment.
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475:During the post-war period, widespread adoption of
97:. Unsourced material may be challenged and removed.
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540:The last generation of power tubes, typified by
815:Mullard ECH83, EBF83 are but two such examples.
288:, all electronic amplification was produced by
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660:low damping factor (High Z out) output stages;
559:family, to the smaller and cheaper noval base
442:Amplifiers during this period typically used
493:Other developments included (among others):
879:] (in German). Vienna: Allegro Verlag.
683:
60:Learn how and when to remove these messages
524:
849:Langford-Smith, F.; et al. (1967) .
590:Valve radios and amplifiers were used in
237:Learn how and when to remove this message
219:Learn how and when to remove this message
157:Learn how and when to remove this message
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316:Origins of electric guitar amplification
182:This article includes a list of general
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403:or equivalents, less usually the octal
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635:equalisations (RIAA, ortho, RCA, 78).
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340:(1952) during the 1950s. The earliest
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95:adding citations to reliable sources
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902:Colloms, Martin (January 3, 1998).
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833:(3rd ed.). Elsevier Science.
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300:Instrument and vocal amplification
188:it lacks sufficient corresponding
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757:Valve audio amplifier - technical
411:Amplifiers for sound reproduction
41:This article has multiple issues.
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275:sound recording and reproduction
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690:List of valve amplifier designs
82:needs additional citations for
49:or discuss these issues on the
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803:"Class AB Power Supply Ripple"
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852:Radiotron Designer's Handbook
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594:until they were displaced by
904:"A Future Without Feedback?"
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941:Theory paper on OTL designs
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259:vacuum tube audio amplifier
21:Valve Amplification Company
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422:submarine telephone cables
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450:eated tubes in a Class A
684:Notable historic designs
698:Quad II power amplifier
525:Tube hi-fi in the 1960s
294:audible characteristics
280:Until the invention of
203:more precise citations.
106:"Valve audio amplifier"
16:Type of valve amplifier
829:Jones, Morgan (2003).
731:Mark III and Stereo 70
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871:Trauenstein, Magnus.
748:Technical information
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586:Automobile amplifiers
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380:, or the lower-power
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251:valve audio amplifier
855:(Classic ed.).
713:Williamson amplifier
481:Williamson amplifier
284:devices such as the
91:improve this article
607:Valve preamplifiers
490:industry was born.
271:sound reinforcement
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622:frequency response
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935:The Audio Circuit
477:negative feedback
416:Early development
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330:Fender Telecaster
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916:Glass Audio
908:Stereophile
778:Valve sound
645:Valve sound
639:Valve sound
592:automobiles
336:(1954) and
282:solid state
201:introducing
951:Categories
862:0750636351
789:References
688:See also:
437:audiophile
286:transistor
184:references
117:newspapers
46:improve it
768:Amplifier
269:used for
52:talk page
762:See also
743:8B and 9
735:McIntosh
463:DH-SET.
446:irectly
741:Marantz
433:talkies
265:) is a
197:improve
131:scholar
883:
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729:Dynaco
454:ingle-
326:Gibson
322:Fender
186:, but
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737:MC275
709:TL/12
569:ECC83
565:ECC82
561:ECC81
520:date.
458:nded
401:12AX7
399:, or
397:12AU7
393:12AT7
257:) or
138:JSTOR
124:books
881:ISBN
857:ISBN
835:ISBN
723:Quad
707:LEAK
629:EF86
616:and
573:EL84
557:6SN7
550:KT88
548:and
546:EL34
542:KT66
504:the
499:LEAK
405:6SN7
382:EL84
378:6550
374:KT88
370:EL34
324:and
310:gain
110:news
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384:in
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