Audio amplifiers
The vacuum tube appears to be the earliest invented amplifier. By pumping all the air out of a glass (non-conducting) cylinder, a thin wire inside (called a ‘filament’ can be heated very hot by driving an electrical current through the wire. But because there is no oxygen inside the vacuum tube the wire does not burn up.
This permits the wire to emit electrons without being destroyed.
At the other end of the tube, the electrons can be “picked up” by a type of plate and thus a current is flowing through the tube from the filament to the plate.
Between the two another charged plate is placed and if there is a small signal on that plate the varying charge on the plate causes a variation of the electron flow between filament and receiver plate.
So this electron flow now varies exactly as the smaller controlling voltage varies on the in-between plate.
So the small signal causes the larger flowing current to become a larger or amplified signal, an exact model of itself as a signal, but now larger and more powerful. The signal has been amplified.
This brilliant innovation was used in radios, telephone companies, televisions and… guitar amplifiers.
The Transistor? Nope.
Later a solid state device was developed which did a similar job but was much smaller and which didn’t wear out over time as do vacuum tubes. This new ‘transisitor’ was also very durable; it wasn’t made of fragile glass.
So in most commercial applications, the transistor became the amplifying device of choice, in the United States. (For historical reasons, both China and Russia did not initially have access to transistor technology, and so they actually carried vacuum development much further creating tiny vacuum tubes so durable they were used in Russian space capsules.)
However, the “softer” sound of vacuum tube amplification remained more popular with many audiophile applications, including amps used for electric guitars. Guitarists just liked the sound of electric guitar amplifiers made with vacuum tubes.
Preamps and Power Amps
To make a more powerful amplifier you simply use several ’stages’ of amplification. First you amplify the tiny signal from a guitar pickup, and then you amplify *that* signal again with larger vacuum tubes that can handle a larger amount of power.
If you’ve ever gone to buy guitar amps and were looking at musical instrument reviews, or stores which offer musical instrument prices you’ll soon notice that nowadays you can purchase both ‘preamps’ and ‘power amps’. The second one — the power amplifier — does all the heavy work.
Typical Guitar Power Amplifiers
The 12AX7 Power Amp — This is not a manufacturer but the name of a vacuum tube model — the 2AX7 (ECC83) dual triode. Although this tube has a high gain it is normally used in preamps, and the idea of using it for a power amp was an odd one. However a designer named Tim de Paravicini undertook the task “because it was there” and the result was unconventional and interesting. The amp he designed uses a battery of these smaller tubes, and produces a sound that handles brilliance well, the sheen of strings and a sweet and compliant sound.
Mesa Boogie Power Amp — Mesa Boogie is famous for using a ‘rectifier’ sound which is distinctive and which very well supports the long sustain of controlled feedback. Carlos Santana and Harvey Mandell both played this kind of long-sustain music.
Peavey Power Amps — The Peavey company has developed a wide range of amplifiers for the guitar market and has several designs which especially cater to the generally-preferred vintage tube sound, including the Peavey ValveKing line.
Traktor Topaz does most web-design and online articles for Mobius Megatar Touchstyle Basses. Makes instruments, too.
His latest website about how to get a cheap electric guitar amplifier that sounds great.
He has also authored a detailed how-to guide to help you shop for a guitar power amplifier on that same website.
Custom Audio Amplifiers w. Suhr Guitar Demo – NAMM 2010 -CAE CAA Bradshaw Electronics TTK 10
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