Jim Kelley Amplifiers
Encyclopedia
Jim Kelley Amplifiers is the trademark for the vacuum tube
guitar amplifier
s manufactured by Active Guitar Electronics of Tustin, California between the years of 1978 and 1985. Approximately 600 of these amps were built during that time. The single channel version of the amplifier employed modest gain in the preamp
stages, Baxandall
bass and treble controls, a split load phase inverter
, and four 6V6GT
output tubes. The amplifier produced 60 watts RMS at full power, and included a half power (30/60) switch. An improved version was released in 1980 which included reverb
and an additional stage of gain. These guitar amps were the first to employ a matched quartet of 6V6GT
output tubes. They were also the first guitar amplifiers to be offered with an optional power attenuator
.
Further innovations were incorporated into the FACS (foot activated channel switching) model, which built upon the single channel design by adding switchable preamps and tone stacks, and provided relay
switching for the power attenuator. Another novel feature developed by Jim Kelley was the LED
Bias
Indicator.
The final model to be developed and produced was the FACS Line Amp. It had all the features of a FACS amp, but the lead channel also employed a low power push-pull output
section. The miniature output transformer
was followed by the Main Gain control, which functioned as a Master Volume. The lead channel also had a post distortion passive LC
tone control which could either cut or boost mid-range. A rack mounted, all FET
stereo
guitar amplifier with analog delay reverb was developed but never brought to market.
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
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 manufactured by Active Guitar Electronics of Tustin, California between the years of 1978 and 1985. Approximately 600 of these amps were built during that time. The single channel version of the amplifier employed modest gain in the preamp
Preamplifier
A preamplifier is an electronic amplifier that prepares a small electrical signal for further amplification or processing. A preamplifier is often placed close to the sensor to reduce the effects of noise and interference. It is used to boost the signal strength to drive the cable to the main...
stages, Baxandall
Peter Baxandall
Peter J. Baxandall was a British audio engineer and electronics engineer and a pioneer of the use of analog electronics in audio.He authored many ground-breaking papers, including but not only ones which describe what is now called the Baxandall tone control circuit.-External links:* *...
bass and treble controls, a split load phase inverter
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...
, and four 6V6GT
6V6
The 6V6 is a beam-power tetrode, introduced by Radio Corporation of America RCA United States in late 1937, and still in use in niche applications.Similar to its predecessor the 6L6, the 6V6 was far more widely used...
output tubes. The amplifier produced 60 watts RMS at full power, and included a half power (30/60) switch. An improved version was released in 1980 which included reverb
Reverberation
Reverberation is the persistence of sound in a particular space after the original sound is removed. A reverberation, or reverb, is created when a sound is produced in an enclosed space causing a large number of echoes to build up and then slowly decay as the sound is absorbed by the walls and air...
and an additional stage of gain. These guitar amps were the first to employ a matched quartet of 6V6GT
6V6
The 6V6 is a beam-power tetrode, introduced by Radio Corporation of America RCA United States in late 1937, and still in use in niche applications.Similar to its predecessor the 6L6, the 6V6 was far more widely used...
output tubes. They were also the first guitar amplifiers to be offered with an optional power attenuator
Power attenuator (guitar)
In conjunction with an electric guitar amplifier, a power attenuator is used to divert and dissipate some or all of the amplifier's excess or unneeded power in order to reduce the volume of sound produced by the speaker.- Explanation :...
.
Further innovations were incorporated into the FACS (foot activated channel switching) model, which built upon the single channel design by adding switchable preamps and tone stacks, and provided relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
switching for the power attenuator. Another novel feature developed by Jim Kelley was the LED
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
Bias
Grid bias
Grid bias is a DC voltage applied to electron tubes with three electrodes or more, such as triodes. The control grid of these devices is used to control the electron flow from the heated cathode to the positively charged anode...
Indicator.
The final model to be developed and produced was the FACS Line Amp. It had all the features of a FACS amp, but the lead channel also employed a low power push-pull output
Push-pull output
A push–pull output is a type of electronic circuit that can drive either a positive or a negative current into a load. Push–pull outputs are present in TTL and CMOS digital logic circuits and in some types of amplifiers, and are usually realized as a complementary pair of transistors, one...
section. The miniature output 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...
was followed by the Main Gain control, which functioned as a Master Volume. The lead channel also had a post distortion passive LC
LC circuit
An LC circuit, also called a resonant circuit or tuned circuit, consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C...
tone control which could either cut or boost mid-range. A rack mounted, all FET
Field-effect transistor
The field-effect transistor is a transistor that relies on an electric field to control the shape and hence the conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are sometimes called unipolar transistors to contrast their single-carrier-type operation with...
stereo
Stereophonic sound
The term Stereophonic, commonly called stereo, sound refers to any method of sound reproduction in which an attempt is made to create an illusion of directionality and audible perspective...
guitar amplifier with analog delay reverb was developed but never brought to market.