Mesa Boogie MkIIa tube guitar amplifier
Last Update 12/09/2017
This Mesa Boogie MkIIa was the first good guitar amp that I
owned. The previous guitar amp I had was a Peavey Classic which
had two problems:
1: it had this midrange "honk" that I
couldn't get
rid of
2: it ate output transformers.
By the time I was
replacing its third OT at a repair cost of $200, I decided to replace
the amp. I asked my repair tech who makes guitar amps that don't
prematurely wear out OT and he suggested Mesa Boogie. In one of
my earliest strokes of luck of being in the right place at the right
time, the tech knew someone who had one for sale. And the price
was good.
The previous owner had ditched the original combo 1x12 package and had
built a replacement combo cabinet, albeit taller so the speaker was
closer to the ears. It was practical but bulky, so I ditched the
homemade cabinet and ordered the optional rackmount chassis so the head
was installed in my keyboard rack where everything was in one
place (I like quick setups). My memory is hazy as it was over
thirty years ago - I
believe I scavenged an empty combo cabinet for the speaker.
I was playing in a classic rock band at the time and the Mesa Boogie
was a big step up. It was a really good sounding amp, 60w with
graphic EQ. MkIIa models offered either the 12AX7 or a "FETTron"
solid state transistor as the front end input - likely all players
stuck with the former. Back then I was not yet wise to the tone
differences
of different speakers, tubes, guitars, pickups, and strings like I am
today. I was lucky that the combination I had then WORKED.
Although I was the keyboard player, our soundman told me he liked the
sound of my guitar setup better than the guitar player in our
group. My guitar player brother whom I grew up with around
several amplifiers takes the blame.
I had bought another Mesa Boogie amp for a good price for the band
practice room. That was the next model MkIIb, similar setup 60w
combo amp with graphic EQ. It sounded very similar, but had this
rasp in the tone that I couldn't get rid of. Had I known about
tone differences of tubes I would had tried swapping them out, but I
wound up selling that amp.
After I left the band I wasn't playing guitar anymore and no longer
needed the MkIIa, so I sold it to a buddy from high school who lived in
the south. I told him that if he ever sold it that I wanted first
dibs. Some years later I got interested in playing guitar again
and he
happened to be ready to sell the amp so it came back in my hands.
One of his buddies had borrowed it and had changed all the tubes - this
was the state I got back the amp and the tone was not at all to my
liking. So I took the amp to my repair tech with the goal of
sorting through his stock of Groove Tubes. I could not find a
preamp tube I liked, so he suggested swapping out power tubes. The
first set of power tubes made a DRASTIC
difference. That was
my first revelation that power tubes make a significant contribution to
the tone of an amp, one that would serve me well when selecting a guitar amp modeller.
With the emphasis this time on recording, I sought to do away with a
speaker cabinet and the hassles of micing it. So I opted for the
Hughes & Kettner Red
Box
which is a direct box with filtering
circuitry designed to emulate the sound of a guitar speaker
cabinet. It does this job very, very well. But because this
amplifier has a tube power stage, it absolutely positively MUST have a
load connected to it. The load can be a speaker (duh) or a
passive resistor. Two important specs of the passive resistor is
that it must equal the output impedance of the amplifier and the power
rating must be conservatively rated. Since this was a 60w
amplifier, I selected a 75w power
resistor. These are not small
components so I mounted the resistor on the back of the front cover of
the rack
case, along with the Red Box. This way the direct connection was
always ready. Stay away from carbon power resistors as they are a
fire hazard as they approach their maximum power rating.
Eventually the capacitors in the amp dried out, I could hear the impact
it was
having on the tone. These amps were built around 1979-1980, and
capacitors
have an average life of 25 years so they were past their expiration
date. I took it to an authorized Mesa Boogie repair
tech who my brother knew and sure enough the capacitors were visibly
leaking. The recap did restore the glory of that amp.
I was happy to have my old amp back, and as I was more active in
writing and recording songs there were other guitar tones I was
seeking. But these Mesa Boogie MkII amps are one trick ponies -
they do one sound and do it very well, but seem resistant to be coaxed
into other tones. I was never entirely satisfied with the
clean
tone of the rhythm channel (I would discover years later later that a
Fender preamp tube in the rhythm channel of my brother's Mesa Boogie
Studio Preamp went a long way to get that glassy clean tone I was
after). The lead channel was the amp's raison
d'etre - the overdrive had a very very good lead tone.
But I wasn't a lead player, I was a rhythm player. It was a great
rhythm crunch for 80s metal and hard rock, but "that sound" was
starting to sound dated. When I was in a band, I was playing
keyboards or
guitar but never both at the same time. Later when I was
recording at home, I began using both at the same time. "That
sound" tended to conflict with the keyboard sounds I was using and it
was hard to get the two to co-exist in a mix. There were other
sounds that I wanted. I was well aware that the interactions of
the settings of the rhythm and lead channels will impact the sound,
alas
any deviation from the control settings from "that sound" didn't sound
good. It would had been an exercise in futility anyway because
the high gain architecture tends to sound the same regardless of tube
choice.
I eventually found the Vox
Valvetronix
amp that gave me much more variety of sounds that I
wanted. It could also get a close approximation of the Mesa
Boogie tone. One of my other frustrations of the Mesa Boogie was
it was too damn loud - I seldom had the master volume above 1.5 and
around that setting the control was VERY touchy (need just a little
more volume ARGH TOO MUCH). The Vox had
power settings for 60w, 30w, 15w, and 1w for lower volume which was
much more reasonable (and neighbor friendly). That made the Mesa
Boogie redundant so I
sold it. To be fair, I had only one guitar at the time and had
yet to appreciate the tone differences of tubes, strats, teles,
speakers, et al. But I don't regret letting it go. It did
make me a tube snob though.
But I never had to replace the output transformer in that amp.
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