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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