Mark III
Thermionic Studios Mesa/Boogie is Serial Number 22797. It is a "Blue Stripe" Mark III with the full control compliment offered at the time:
- Reverb
- Simul-Class power amp section
- Graphic Equalizer tone shaping
Since it is currently in a state of disrepair, we're going to have to get inside and fix up quite a bit before it's ready for rental.
According to the Mesa/Boogie website, only around 13384 Mark IIIs were ever built. Given our serial number, we believe ours was built sometime in the middle of 1988. Once we get inside to refurbish it, we'll have a much better look and be able to date it more accurately.
There are several different "flavors" or editions of the Mark III:
Red Stripe: The third revision of the Mark III amp was the "Red Stripe", which featured a red marker stripe above the power cord. The amplifier had increased gain over the purple stripe, and lead mode circuitry almost identical to the IIC+. It was produced about 12/86 to 1/88 and included serial numbers 18949 to 21863.
Here is something rather special to note regarding the Green Stripe / Simul-Class Mark IIIs:
“In Simul-Class, the amp must use two 6L6s in the inner tube sockets for 60 watts Class A/B, and two EL-34s (or 6L6s) in the outer sockets for 15 or 25 watts in Class A. So, on a Mark III Simul-Class amp, when the switch is UP ("Simul-Class"), you get 75/85 watts. This is all four power tubes. Switch DOWN ("Class A"), is 15 watts. Only the outer pair is on.”
From Mesa/Boogie:
In March of 1985, the Mark III introduced the world to three footswitchable voices in one amplifier and took its position as the flagship of the line, the next step in the evolution of the Mark Series Family of amps. The Mark III, like the Mark II had a few different versions over the period it was in production but rather than indicate the changes as an A, B, C or C+ model, the chassis was marked with a stripe or dot of different colored markers above where the power cable meets the chassis to indicate the revision.
As with all things MESA, what these various stages represent are a matter of opinion with respect of the sound character. They represent snapshots in time of the development of an amplifier line. If the amplifier gets you the tone you want, the jiffy marker is nothing more than a mark of its vintage.
The order of these versions and what one can expect to notice from version to version is as follows:
Categorization
No Mark, Black Marks
- Early Mark III
- These are lean and powerful amps with more output power than a Mark IIC+
Purple
- Rhythm 2 was shaped to be more "rounded", have less gain, with improved level.
=== Red ===: Rhythm 2 & Lead Mode Tweaked
- Rhythm 2 was further developed and is very hot.
- Lead mode was also tweaked to close in on the Mark IIC+ sound. It was produced from around 12/86 to 1/88 and included serial numbers 18949 to 21863.
Blue
- Reshaping of Rhythm 1, more aggressive preamp gain, Power section made akin to IIC+
Green / Simul-Class
• Cleaner Rhythm 1 & Lead channel reshaping
- Unlike other Simul-Class amps, these Mark III's were wired in Pentode (not triode) in the Class A sockets for more power.
- Power section is same as Blue Stripe/Dot otherwise
Additional Sources:
- https://mesaboogie.zendesk.com/hc/en-us/articles/218914817-When-was-my-amp-made-
- https://mesaboogie.zendesk.com/hc/en-us/articles/115003821874-What-Version-Mark-III-do-I-own-
- http://tubefreak.com/fschema.htm (gif images)
- https://forum.grailtone.com/viewtopic.php?f=27&t=74647 (cleaner Mark III black dot images)
- https://schematicheaven.net/boogieamps/boogie_mkiii.pdf
