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Mesa Boogie Mark IIA

1980 – Mark IIA Mesa Boogie pioneers yet another development in guitar amplifiers with the Mark-II, the first channel-switching amplifier. Before long, separate channels for rhythm and lead will be commonplace.

Make and model Mesa Boogie - Mark (II)
Power (Watt) 100 W
Type Combo
Channels 2
Footswitchable channels Yes
Lamps
Power lamps 4 x 6L6GC/6P3S
Preamp lamps 4 x 12AX7
Rectifier Solid
Effect loop No
Effects Yes
5 Band EQ
Reverb Yes
Impedance 4/8/16
Size
Weight

Mesa-Boogie-Mark-2A

Other specifications:

  • Available as Head or 1×12 Combo
  • 60/100 WATT combo
  • ElectroVoice (EV) 12L speaker
  • Reverb
  • 5 Band EQ
  • Pre-out/Power amp
  • Slave out

The Mark II introduced channel footswitching, and wasn’t referred to as the Mark IIA until the Mark IIB was issued. It was also available as a head, which could be hooked up to a number of different speaker combinations, although a 1×12 cabinet was typical. However, the reverb circuit is considered noisy and the footswitching made a popping sound when used; both of these features were later improved on the Mark IIC. The preamp gain on the Mark IIs occurs after the tone controls and so, according to Mesa/Boogie, the IIA has a tighter, more focused sound than the Mark I.

The IIA and IIB, and some late-model Mark I amps, used a silicon device called fetron in place of one of the 12AX7 preamp tubes, and included a switch for configuring the amp for either fetron or 12AX7 operation. The reason for using a fetron was to address some of the problems associated with microphonic 12AX7 tubes in a high-gain situation; its use was later discontinued.


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