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This switch selects between two-tube and four-tube operation in the power section. In the CLASS A position, only the two end power
tubes are active, producing around 30 watts before clipping when operating TRIODE, or 50 watts when in PENTODE. For the nastiest
shredding tone and the greatest amount of power amp distortion, use CLASS A with TWEED
POWER and TRIODE.
In the SIMUL-CLASS position, the middle two 6L6’s switch on in parallel with the end tubes and
the total output is combined through our unique output transformer. You’ll find an increase in
low-end punch as well as overall volume as the power kicks up to around 85 watts PENTODE
or 70 watts TRIODE (power ratings based on standard U.S. music amp specs which call for 120
volt A.C. Mains and allow 5% distortion).
When you deliberately push the power section into clip, the wattage continues to rise, peaking out at about double. The MARK IV
provides an external jack for the power switching function so this feature can be programmed to operate in sync with, say, RHYTHM
2 via a MIDI switcher such as our MIDI Matrix.
NOTE: For the external jack to function properly, the mini-rocker switch must remain in the CLASS A position.
This switch affects the LEAD mode only. Most noticeable is the big increase in gain and sustain when MID GAIN is selected. This
added gain is focused in the mid-range “punch” region and is most noticeable when the LEAD DRIVE control is set very low - at the
“threshold of distortion” point discussed earlier. Using this low setting with the MID GAIN on
(switch in the down position) produces a punchier, fatter blues sound, especially when used
with Pentode and Simul-Class.
As the setting of the LEAD DRIVE control is increased, the MID GAIN continues to add huge
amounts of extra boost, which at some point will become overwhelming and will cause unnec-
essary noise, squealing and feedback when used in conjunction with the LEAD BRIGHT and
LEAD FAT switches. For loud high-gain lead playing most seasoned veterans will prefer the
switch in its HARMONICS position (so named because it produces a carefully balanced har-
monic spectrum rather than the blatant mid-boost sound). To duplicate the sounds of our fabled MARK II-C, switches should be set
for HARMONICS and TRIODE, with the PRESENCE controls pulled out. This produces a great balance between punch, smoothness
and rich overtones to deliver a guitar voice that’s truly classic! Notice that hiss, noise and feedback levels are extremely low for an
amplifier with this much gain.
This procedure is in keeping with Mesa/Boogie’s quest for ultimate versatility. As you know, different tubes offer different sounds and
playing characteristics and your new MARK IV offers four choices: FIRST: the standard four 6L6’s which produce by far the best all-
around performance. They deliver the most powerful clean sounds along with the richest distortion. SECOND: Type 5881 is similar to
the 6L6, but these tubes are just slightly less powerful. Although they will produce a somewhat rounder, more “vintage” tone. THIRD:
For those seeking the traditional British edge to their overdrive sounds, EL-34’s can replace the 6L6’s in the end two sockets (outer-
left and outer-right). When running the amp in class A, only the two EL-34’s will be operating. In Simul-Class, a combination of two
6L6’s plus the EL-34’s produce a louder, fatter sound while retaining the British edge. (Expect the clean sound to suffer a bit whenever
EL-34’s are used.) All combinations of Triode, Pentode, Tweed and Normal power can be used with this EL-34/6L6 combination.
FOURTH: Those of you who recall the great sounds of old Fender Deluxes will be delighted to know that four 6V6’s can also be used
in the MARK IV...but, ONLY when TWEED and SIMUL-CLASS are selected. Also, to reduce tube wear when using 6V6’s, the 8
REAR VIEW MKIV
(Continued)
SIMUL-CLASS / CLASS A SWITCH:
LEVEL OUT
POWER AMP
TRIODE SIMUL-CLASS HARMONICS
PENTODE
CLASS A
SPEAKERS
8 OHM
4 OHM
4 OHM
MID GAIN
LEAD VOICING
2
3
4
5
6
7
8
9
1
0
10
2
3
4
5
6
7
8
9
1
0
10
PAGE 12
HARMONICS / MID GAIN SWITCH:
LEVEL OUT
POWER AMP
TRIODE SIMUL-CLASS HARMONICS
PENTODE
CLASS A
SPEAKERS
8 OHM
4 OHM
4 OHM
MID GAIN
LEAD VOICING
2
3
4
5
6
7
8
9
1
0
10
2
3
4
5
6
7
8
9
1
0
10
POWER TUBE SUBSTITUTION: