Rectifying the Rectifier

Written on: 29sep2025 --- Updated on: 20oct'25 | View v1 (29sep'25)

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The Rectifiers were a focus for me for a long time, and I still love the circuits a lot. My curiosities first got started when I read forums that mentioned the 2ch.'s 1Meg gain pot (as it says in the schematic) is actually 250k. This lead me to read more and more and more.. until I found some claims that the Red Presence is actually 100k instead of 25k, and that really piqued my autism. So, I thought about sharing the years of research, hence this post.

The time before the light

I won't delve much into the oral history of the whole thing, but the circuit is largely just an SLO, despite what Mesa or their fanboys claim otherwise. So what has been changed and what not? (purely talking about the high gain modes, not the clean mode on the 2ch.)

So yes, that is basically an SLO with higher voltages (less fuzzy distortion), a more 'tight' pre-distortion filtering, a very different FX loop, and a revoiced tonestack and NFB circuit. Few changes, yet many big impacts!
It is also worth noting that the clean channel stays connected on an SLO-100, which leads to the clean channel bleeding through when the overdrive channel's gain is at zero. This also loads the SLO's first gainstage more, although I do not know how this affects the feel of the preamp.

Genesis

The first Rec released was the '2ch.', which has no official name other than being the quintesencial amp people thing of, and it is also what sparked my interest, but regardless. It has five known revisions; C/D/E/F/G. While the next part is pure speculation, based on gut shots I believe C&D, E&F to be largely the same, with RevG circuit-wise being again the same as E&F but with different transformers.
These original units have some cool quirks like Org presence working on Red Vintage, allowing you to use both presence pots, or the fact you can make the clean channel into modern voicing (only possible on the 2ch.s!).

So to go into further detail of that table:
Red presence used to be 220k for the 'pre-500', which Fluff's site lists as not being close to RevE, which is interesting because those two revisions I know for certain have the old clean channels. Later revisions like RevF and RevG for sure used 100k pots (thanks Bret!).
The clean channel on the C&D used to be bypassing the first gain stage (like plugging into a low input of a 2203), meanwhile the later E&F&G use a giant pad before the gain pot. They effectively achieve the same thing but in different ways; none is better or worse.
As far as I know all models up to the RevF all used the 561136 power trannies, while the RevF began switching to 561140 and RevG uses 561140 completely.

Everything largely, if not completely, stayed the same. The biggest differences are in the tonestack and clean design between C&D and E&F&G. The RevG has a parallel loop as well, not that it influences the sound.

Schematics of the different revisions:
->Pre-500

->RevF Correct
->RevF Falsified
->RevF Fixed

->RevG w/ tech notes (still a RevF schematic)
->Trem-O-Verb - Despite this not being a solo head, it still is very much a standard Rec and is seemingly based around the RevG circuit with some slight tweaks, and of course the tremolo and reverb.

Genesis: continuation

The success of the '2ch. Solo head' seemed to really go to Mesa's head at the time and thus you have non-Rectifier circuits with the 'Dual Rectifier' logo and name, like the Blue Angel and Maverick.

Non-Rec schematics:
->Maverick
->Blue Angel

The dark ages

I call this the dark ages, because I like the 3ch. Recs the least in both design and sound. There's nothing wrong with them, but I have to name this paragraph something.
There are many revisions of these as well but they're so minute that it barely matters. Just the earlier ones clinged onto the 561140 trannies while most used the 561160. The biggest and as far as I can tell only change is that V2a's grid JFET and cathode relay got switched. A common problem was (and still is) that these J175s leaked voltage onto the grid and that would make the tube unhappy.

So to explain the table:
-Ch.2 Raw's voicing is rather unique, it has a 25kB (linear) in the tonestack, and NFB. Because the NFB is on without having an NFB presence, it means that it is perpetually set to zero. I think this voicing can best be compared to having Ch.2/3 on Vintage and having the presence at null.
-Ch.2 Vintage's voicing is the classic 2ch. Orange Vintage, nothing got changed
-Ch.2 Modern's voicing is the classic 2ch. Orange set to Modern, once again nothing got changed, and that does mean the presence pot barely does anything. From my experience such a setup just means a slight midboost the higher you set it. Emphasis on the slight, because it might as well not be anything

-Ch.3 Raw's voicing is like the Ch.2 Vintage voicing, but with a 100kB pot, meaning that most, if not all, of the rotation is pretty useless. This channel is very much voiced and biased for being in Modern.
-Ch.3 Vintage's voicing is Ch.3's Raw verbatim.
-Ch.3 Modern's voicing is that of the 2ch. Red Modern, nothing got changed. Out of all the 3ch. voicings, this is the only one to have a 680p treble cap, shifting the mids.

Schematics of the different revisions:
->3ch. early
->3ch. Late - see page 8 for the difference; very minute.

Renaissance

And thus the lord (John Marshall, no joke, a guy named Marshall designed many Mesas :) gave us the Multi-Watt, or alternatively known as the 'Reborn' due to marketing flyers and forum regurgitation. Despite these things being visually identical to the 3ch., they have a completely redesigned PCB (for better and worse) and the scope was narrowed a lot more. The MW is like a 'best of', the (in my opinion) less interesting modes have been cut.

As a quick rundown:
-Raw has once again been revoiced, and is like 3ch. Ch.3's Raw, except with a useful presence taper
-Vintage is 2ch. Org Vintage, but with a better presence taper
-Modern is 2ch. Red Modern

To expand on the taper change: the 'Raw/Vintage presence' (the one in the negative feedback) got changed from 25kB (linear) to 25kC (reverse logarithmic). A good change, because with 25kB you'd only get the presence active at the last 10% of or so, while with a 25kC that 10% is at noon, thus giving you more nuance in the 'high treble' zone of the presence rotation. This makes the vintage/Raw modes a lot more sizzly/treble with everything set to noon, but also more usable in my opinion.

The Gibson ages

Remember when Gibson bought Mesa in 2021? Long time ago, and yet the Badlander was released in 2020, but it doesn't deserve its own chapter. The Badlander, despite what Mesa and youtube shills try to claim, isn't a Rec. Neither a 'Dual' (as in, diode and tube rectification) or 'Rectifier' (having an SLO-based circuit). It actually is just a dumbed-down Mark circuit, and mirrors the Mark7 a fair bit (maybe the unreleased Mark6 Randy Smith spoke of?).
And then comes the 2ch. Reissue, which like most Gibson reissues, isn't even close to a carbon copy of what they claim. I don't have any circuit info on it, but by looking at the PCB... it definitely isn't a '90s Dual Rectifier'.

->Schematics of the Badlander

The oddballs

I obviously haven't touched on the RoadKing/Roadsters, Rectifier Recording Preamp, Single Rectifier Solo Head / Rect-o-verb or the Mini Rectifier / Rect-o-verb. They're oddballs and not just 'Rectifier circuit with one pair of 6L6s'.

Singles came in four versions, Series 1 Solo Head (classic, non-reverb) and Rect-o-verb (solid state reverb) and Series 2 Solo and Rect-o-verb. The difference between a Solo and Verb is the ommitance of the reverb circuitry and a different headshell design, much more reminiscent of the Trem-o-verb.
-The Series 1 might be my favorite design out of all of them, because it is generally speaking a 2ch. Red channel with a 3ch. ch.1 (green) channel tacked on. The only real difference between the 2ch. and Single Series 1 is that the treble cap isn't 680p but rather 500p, thus shifting the mid frequency upwards. Like the 2ch, when on Modern only the Red presence works, but on Vintage both work.
-The Series 2 is just like a Series 1 but with a 3ch's 3rd channel (red) presence switching. Once again the tapering has been messed with so it's not something you're ever gonna find on a 2ch.

The Minis came in two versions, a Solo Head and a Rect-o-verb.
The preamps are once again identical and it's merely the omittance of the tube reverb and redesign of the FX loop a little. The Solo has a bypassable FX loop, the Verb doesn't. The rest of the amp is ripped from the Multi-Watt, just lacking the Raw mode and having some things tweaked for the lower voltages and different output tubes, presumably.

Now the Road series.
-Starting chronologically with the RoadKing1. The RK1 is basically just a 3ch. Rec but with an additional clean/pushed channel, although only the clean/pushed channels having been revoiced a little here and there. What also got changed was the first high gain channel (Ch.2 on the 3ch., Ch.3 on the RK1) got changed from having NFB enabled and preamp presence to NFB enabled and poweramp presence. What it also has is: two FX loops, solid state reverb (like from the Single Recs), and speaker switching. Only talking about the high gain channels (3&4) it's really just a 3ch. Rec.
-The RK2 now has tube reverb again, modifies the clean/pushed channels even further, but the high gains stays the same barring Ch.3: instead of a 25kB pot, it has a 10kC pot like they would end up doing on the Multi-Watt later on. This channel isn't suited for Modern, only if you like the presence on 1 or 0.
-Then comes the Roadster, different name, same clean/pushed and high gain circuits. Simpler FX loop and no speaker switching, so just basically a dumbed down RK2.

As for the Rectifier Recording Preamp, it's like a very basic RK1 Ch.2 set to clean, and a 3ch. high gain channel, always with a preamp presence, switchable 500p/680p treble cap (vintage/modern), and the modern adds a Mark-style fixed GEQ in there for that XXXtra midscoop.

Assosciated schematics:
->Single Series 1
->Single Series 2

->Mini Solo Head
->Mini Rect-o-verb

->RoadKing1 Early
->RoadKing1 Late
->RoadKing2
->Roadster
->Roadster Alternative bulletins

->Recording Preamp

Addendum

If there are any mistakes, improvements, or even anything to add, please do send me an email at:
Thanks for reading! :)
-MB

v2 was mostly based on suggestions/recommendations from a friend, to whom: thanks! :)