For sale is my vintage Mesa/Boogie Mark IIB Coliseum – Series 300 head, serial K136 (see rear-panel photo). This is the rare high-power Coliseum/300 Series version, built for huge headroom, punch, and that classic Mark lead channel with the onboard 5-band graphic EQ.

How it sounds (the reason to buy it)

This amp sounds incredible: massive power on tap, ridiculous low-end authority, and a feel that’s bigger than a “normal” Mark.

• Clean channel: crystal clear, very fast and “hi-fi”, with immense headroom—it stays solid and wide even at loud volumes.
• Crunch / edge-of-breakup: tight, dynamic and punchy; it does that addictive Mark “chewy” midrange grind.
• Gain / lead: aggressive and articulate—it roars when you push it, with that singing sustain and harmonics, but still stays focused (not flubby).
  With the graphic EQ you can go from classic scooped Mark tones to thick, mid-forward rock/metal voices in seconds.
• The effects loop works perfectly and plays great with time-based effects (delay/reverb/modulation) — clean, quiet, and very usable.

Key features

• Mark IIB Coliseum / Series 300 chassis (rear plate marked “Series 300”)
• 5-band Graphic EQ (80 / 240 / 750 / 2200 / 6600 Hz) with EQ in/out switching
• Classic Mark IIB control set: Volume 1, Treble (Pull Shift), Bass, Middle, Master 1 (Gain Boost), Lead Drive (Pull Lead), Lead Master (Pull Bright), Presence
• Speaker outputs: 1 × 8Ω and 2 × 4Ω jacks (rear panel)

Voltage / transformer history (important)

The previous owner told me the amp was adapted for European use. The original US 110V transformer was removed and is included separately (the loose transformer you see in the photos, labeled “TRAS. ORIG. 110V AMERICANO MESA COLISEUM”).

I’m reporting this exactly as it was explained to me; I did not personally perform the conversion.

Condition

Cosmetically it shows normal vintage wear (see photos), but overall it presents very very well for its age.

Internals are shown in the gut shots and a youtube video so you can evaluate originality/condition yourself.

What’s included

• Amp head
• 110V transformer in the pics is also include
• Thon Hardcase to safe shipping !