Mesa/Boogie Mark Series
Randall Smith began Mesa/Boogie with a practical joke: he borrowed a Fender Princeton (a small 12-watt amplifier) from his friend, Barry Melton of Country Joe and the Fish, and "hotrodded" it by replacing the amplifier section with a powerful Fender Bassman amp and installing a 12-inch speaker instead of the original 10-inch.
Finally, Smith talked to Richards and they agreed that he would send them an amp, and that the Stones would pay for it or return it.
Examples of this amp in its original form and in good condition are sought after by collectors and guitar aficionados.
These amps had a point-to-point wired power section and had large transformers with great headroom.
It was also available as a head (a standalone amplifier), which could be hooked up to a number of different speaker combinations, although a 1x12" cabinet was the most common.
The new footswitching system relied on a relay, which made an audible popping noise when switching modes.
The Mark IIB is credited as the first guitar amplifier with a tube-buffered effects loop.
The Rear control panel was altered to accommodate the FX Send and Return jacks.
The Mark IIC finally remedied the two major problems of the IIA and the IIB: the previously noisy reverb circuit and a footswitching system that produced a popping noise when activated.
The Mark IIC featured a quieter footswitching system based on optocouplers to reroute the signal, and a new mod to the reverb circuit.
The reverb modification involved resistor swaps and a change in ground lead placement.
The Mark IIC also featured a new Pull Bass shift on the front panel, which slightly extended the low frequencies in the preamp.
The Mark IIC+ was the last of the Mark II series and featured a more sensitive lead channel - due to its featuring a dual cascading drive stage - whereas the IIA and IIB had a single-stage drive circuit.
However, there are some very early "transitional" C+s (in the 133xx range) with gain boost on the panel, but it works the same as the pull Deep on the later versions.
A practical, non-cosmetic method for determining whether a Mark IIC is a C+ is the "Loop Test":[4] 1) Plug your guitar into the Effects-Return-jack 2) Switch to lead-mode 3) Turn the Lead Drive and Gain controls with a note ringing.
Most Mark IIIs have presence and reverb on the back (except for long chassis') unless not desired by the buyer; Graphic EQ was also optional all in either head or combo format.
Mark IIIs contain either four or five 12AX7 tubes in the pre-amp section, depending on if they have the reverb option.
The power circuitry and presence cap remained identical to the previous stripes however.
The lead channel was voiced so brightly, it is considered to be the most aggressive Mark Series Boogie ever introduced.
The presence cap and voltage rating of some of the orange drops in the power section were also altered to mirror that of the IIC+ The final revision was the "Green Stripe" Mark III, which was only available in a Simul-Class format.
It was identical to the Blue Stripe, apart from having its overall gain reduced, except for the wiring of the outer two Class A power amp tubes which were switched to Pentode operation instead of Triode for a 10w RMS increase over previous Simul-Class amplifiers (15w/75w) making 25w/85w.
Mark IIIs were still in steady production around 1994, and finally ceased as late as 1997, 11 years after their launch.
The "crunch" channel is designed for use by hard rock and heavy metal rhythm guitarists.
Some differences: Version A has no stereo effects loop or footswitch for reverb, and the lead channel is much like the Mark IIC+s.
Much like its close cousin, the Triaxis Preamp, it features many voicings based on previous Mark Series amplifiers.
It has three distinct channels, each with their own pre-gain three band tone stack, gain, master, and presence controls.
Similar to the Express and F-series amplifiers, the graphic EQ also had channel-assignable contour-knobs.
It is a smaller, two-channel version of the Mark V. The output section contains two EL84 tubes which can be switched between 10 and 25 Watts.
It also features a built-in CabClone which can be used to emulate a speaker cabinet while driving headphones for silent playing, or a direct-in (DI) box for recording or sound reinforcement applications.
It has three distinct channels, each with their own pre-gain three band tone stack, gain, master, and presence controls.
