2-Channel Dual Rectifier

Revisions, Years, and Serial Numbers:

            The Dual Rectifier (DR) began R&D in 1989 and was first released to the market in 1992. The amp was modeled after the Soldano SLO-100, which is a high gain version of a super hot-rodded Marshall. Mesa expanded on the SLO-100 design, which was revolutionary in its own right by introducing a new version of high gain. One notable difference between both amps (but certainly not the only one) is that the SLO uses a Cathode follower for the effects send whereas the DR uses it for the input of the tone stack. Sonically, the DR is darker and more compressed than a SLO-100.

            Revisions A and B of the DR seem to be prototypes only. Since the first documented Revision C is R-0005, then the first amp, R-0001, last located in Germany, is most likely a Revision C as well because it would have taken too long to get new circuit boards from their suppliers in order for it to be an A or B. Revision D came around the late 200 serial numbers (approx. #280) and finished its run in the very early 500’s, between #506 and #513. Revisions C and D lasted between February 1992 to around August 1992. #505 (seen left ) is the last documented Revision D.

          

            In late August or early September of 1992, Revision E was introduced. #514 is the earliest documented Revision E. This revision had a short life that ended between  #628 and #653. The last accounted for Revision E is #627. Its short life is most likely due to the fact that it seems to be missing many connections on the bottom trace, which led to point-to-point connections to resistors and LDR's. After Revision E, Revision F was introduced at or slightly before #654. It began in late 1992 or early 1993 and lasted until Revision G, the final revision, was introduced in late 1993 or early 1994. Revision G started sometime around #2822-3000 and lasted until the 3 channel Rectifiers were born in 2001.  These started with the approximate serial number #16,000. Users have seen the 2 channels #14,4xx in January of 2000 and #15,18x circa 2000. The 3 Channel Rectifiers were introduced around late 2000 or January 2001.

 

Transformers and George Lynch:

            Amplifiers up into the #2800 serial number range (still Revision F) and possibly beyond are unique due to the transformers they use.  This poses the question of whether these early amps are unique in tone due specifically to the transformers and/or the circuit design. They used the 100-watt output transformers from the MarkIII, made by Schumacher. There is usually a two-year difference in the year of production of the power transformer, usually 1992, and the output transformer, usually dated late 1990.

            The most notable association with the transformer theory is directly linked to George Lynch, who was one of the first to speak about the uniqueness of the first 500 Rectifiers. It has also been written that George looked at the circuit boards for a distinguishable mark that was used to identify these amps. It can be assumed that he was looking for the circuit board revision, serial number, and transformer markings. Mr. Lynch, like many other famous guitar players, may have stated that it was the transformers that made the early DR’s so different, when in reality he was providing useless information to throw other players off the source of his tone. As many seasoned players know, this is not an uncommon tactic. George’s main amp was actually destroyed by Don Dokken who threw drinks at the amp during a gig because he was upset with the loud volume. The amp was never repaired.

Some of the very last 2 Channel amps have the newer 3 Channel transformers.

 

Early Rectifiers’ Transformer Numbers:

Output Transformer: 562100 EIA606-XYZ (the MarkIII 100-watt transformer)

Choke:                          550381 EIA606-XYZ

Power Transformer:  561136 EIA606-XYZ

Export Power Transformer: 561137 (It’s bigger than the USA domestic unit)

The “XYZ” portion of this number contains information on the year and week the transformer was manufactured. For example, the number 302 would signify a 1993 (3) production year that was made during the second week of the year (02).

 

“Pre-500” and “Pre-1000” Lore and Hype:

            For nearly a decade, little was truly known about Pre-500’s and what they exactly were. It was believed that Pre-500 meant the presence of one of the special transformers. However, it is now known that the transformers extended well beyond the 500th serial number, effectively putting that myth to rest. It has also been said that the term Pre-500 referred to either a C or D revision. However, it has been proven that Revision D extended beyond 500 as well. Therefore, it can technically be argued that the term “Pre-500” no longer truly refers to anything special aside from simply the first 500 DR’s.  I say technically because Revision D ended so closely after the number 500, that the term bears some sort of recognition. Revision E has not been studied enough to create any sort of Pre-6XX term. Only time will show whether this revision is similar to Revision C and D or to Revsision F and G.

            The term Pre-1000 also has no specific reference to anything in particular aside from simply the first thousand amps. The term was coined when it was seen that the transformer myth extended well beyond 500. However, it was soon proven that the special transformers extended beyond 1000 (and even 2000) as well. Therefore, this term no longer bears much merit either and should be avoided because it may confuse unknowledgeable buyers and sellers.

            Many sellers often use these two terms to market their amps. However, few of them truly know what they are selling and what features are special. Therefore, beware of sellers that use these terms as marketing gimmicks. The best defense is knowledge of what to look for and what to ask. Sellers that are unable to answer your questions (because they haven’t read this guide!) should be advised as to where to look for the markings.

            One thing is for sure though. These amps are definitely not “hype” that was created to boost prices in the used market. These early amps have a legitimate difference in sound as explained later. Whether or not that difference is subjectively pleasing to your ears is up for you to decide. I always tell others it only takes the first chord to hear the difference.

 

The Identifiable Changes—How to Identify 2 Channel Rectifiers:

            These early DR’s can be identified very easily to the trained eye. Be cautious of sellers who try to sell an early DR without proving some of the following:

• Serial number (see Revisions above)
• Small “Mesa Engineering” logo on the front of the head shell

 

• Smooth black leather covering (not on all of them though; mostly the early ones; I have seen several Pre-500’s with the rhino, bumpy black tolex)

• Serial effects loop — This can be identified in the back of the amp by the presence of only a Send knob and one arrow pointing to the jack.

• The revision printed on the board next to the 4 big blue capacitors (potentially deadly to the touch!). It will read RF-1C, RF-1D, RF-1E, or RF-1F

• 1992-1993 final handwritten tech date for the earliest DR’s. The signatures may include GM (George Mueller) and MB (Mike Bendinelli). DW (Doug West) is a possibility as well, though very unlikely.
• Attached power cable (which actually helps to reduce hum from the amp)
• A speaker output impedance configuration of 8-16ohm, 8-16ohm, 4ohm, 4ohm

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The following changes *mostly* all took place when Revision G was introduced. As discussed later, there were some anomalies.

• Higher Serial Number (obviously)

• Large “Mesa Engineering” logo on the front of the head shell. This appeared a few thousand amps into Revision G.

• Tolex covering

• Parallel effects loop — Identifiable by the presence of two knobs (Send and Return) and two arrows pointing to the jacks. This appears on every Revision G.

• The Revision RF-1G printed on the board next to the 4 big blue capacitors (potentially deadly to the touch!)
• Detachable power cable. Appeared after a few thousand amps into Revision G.
• A speaker output impedance configuration of 16ohm, 8ohm, 4ohm, 4ohm

           

The Transitional Anomalies:

            As with most transitional periods in Mesa history, there are certain features that overlap. The Rectifiers are no different and the most visible differences are the following two:

1) All Revision G's have parallel loops and all Revision F's have serial loops. But whereas all Revision F's have a serial loop, small logo, and attached power cord, there are some G's that carry over the attached power cord and a small logo in addition to a parallel loop. This is contrary to later Revision G's that have a detachable power cord, large logo, and a parallel loop.

            This statement can be proven with the following picture. As can be seen, despite the presence of an attached power cord, there is a parallel loop and small logo (though you can't see it here). I have seen this trend in amps up to around #R-00544x, although it almost certainly goes beyond that. I have seen it as early as #R-0306x.

If you have a parallel loop and wish to mod it to a serial loop, it's a very easy mod to do. It literally takes 2 minutes of soldering 2 wires. An authorized Mesa technician can do it.  However, modding to a serial loop defeats the Solo function on a 3-channel Rectifier.

 

2) The second anomaly is found on the speaker impedance jacks. Revisions C-F have a configuration of 8-16ohm, 8-16ohm, 4ohm, 4ohm. Revision G's have a configuration of 16ohm, 8ohm, 4ohm, 4ohm. HOWEVER, I have found a Revision G in the #R-0054xx range that has the first, older configuration. Like other Revision G's in this range, it has a small logo, attached power cord, and a small logo. This amp can be seen below. The resolution is small, but trust me, it's the same amp. Is it possible the latter confirguration came much later when the large logo came about? Perhaps...

 

Chrome/Blackface:

For some reason, many of the early DR’s bear a chrome chassis and black diamond plate. This is the  opposite of the classic Rectifier design of a black chassis and chrome diamond plate. Contrary to what some may perceive, not every early Rectifier is dressed in chrome/black. Many were dressed in the classic black/chrome design as well as black/black and a very few chrome/chrome. In fact, R-0001 (below) bears the classic  black/chrome design. Today, anything other than the classic black/chrome design is a custom option. It has not been researched whether or not it was also a custom option back in the day.

 

 

So, How Do They Sound?!:

            Revisions C and D have been tested back to back under ideal conditions (same tubes, cables, cab, settings, guitar, etc.) by several people and each has noted that they sound almost identical except the fact that C is noticeably brighter than D. However, the differences are minimal enough that you can just turn the Presence pot to make them sound the same. Therefore, if seeking a C or D, it does not matter much as to which you get, unless one is seeking collector value. It can be said that C is more of the true “Solo Head” whereas D is geared slightly more for rhythm due to its slightly darker nature. The difference in the presence is not the only difference in preamp design between these two versions. Sonically speaking however, this is the most noticeable difference of any interest to guitarists seeking to sculpt their tone.

            The distortion on C and D is very organic and warm. It is creamy, and aggressive, yet still very smooth. Notes jump off the fret board with fierce attack and bite. Under high gain, chords retain incredible clarity in their note's definition (provided you have a decent guitar). The amps are tighter than other DR’s, but are nowhere near as tight as a Mark Series amp. Tightness can be improved with the addition of an overdrive pedal or external EQ. Turning the gain up to 2:00 or 3:00 reveals a very satisfying saturation and compression that does not mush. The lead sound for solos is creamy and smooth, but not as smooth as a Mark Series amp. It is its own unique sound that can stand on its own, but benefits from the addition of an overdrive pedal. The cleans on both C and D are not very good at all, to say the least. They have very low output and are not chimey, despite cranking some of the knobs. The original owners manual states to run the clean in Red Mode for less negative feedback and a better clean channel.

            Revision E is still too new to public knowledge for any comparisons to have been made. One can only assume it sounds like the connection between D and F. The only recording of a Revision E known to public knowledge can be found on the Sound Clips page.  It sounds like an early DR, but the clip is not sufficient enough to justify saying how it differs from other revisions. I do not know how its cleans are, which would be a good indicator of its likeness to the other revisions.

            An individual once quoted Revision F as being between C and D in terms of tone (not sure what that means). However, it does have a looser feel, which translates to less fierce attack and bite. The sound is darker than both C and D, making it great for rhythm. Most notably though is the general consensus that F has great cleans as compared to C and D. Aside from these differences, it still retains most of the early Rectifier characteristics. An overdrive pedal can bring it closer to the aggressiveness on C and D.

            Despite being the last revision, Revision G still has a great sound. This is the sound that defined many of the recordings of the late 1990’s and early 2000’s. It has an even looser feel than Revision F and plenty of bass. Revision G’s do not carry the famous transformers. However, this doesn’t mean they suck! It has the classic Rectifier growl, but lacks the aggressive feel of C and D. It has decent cleans.

            It is worth noting that most of these amps sound great at lower volumes and even better when cranked. This is partly due to the circuitry within DR’s which places all the gain and tone shaping in the preamplifier, as opposed to something like an old Marshall or Fender Twin that relies on volume to get its distortion.

            The early amps sound great with flat settings alone; extra tweaking is almost unnecessary. Simply put, they have “mojo.” These amps were all shipped with STR-420 6L6 tubes and 5U4G Rectifier tubes. STR-420’s are very “sweet” sounding tubes with a low to average life span. They have been discontinued by Mesa. These tubes can be found today as “coke bottle” 6L6’s. 5U4G’s offer less sag (tighter sound) and are still available. Late 2 Channels and early 3 Channels shipped with STR-430, or Sovtek 6L6WXT’s.

 

Why Did Mesa Go Through So Many Changes?:

            It can only be assumed that Mesa went through all these changes because they are a very innovative company that is continually learning and perfecting their designs. They never settle on one design, as has been proven with the many versions of the MarkI-V. Furthermore, speculation exists as to whether Mesa altered the tone on their early “shred” revisions to cater to the “grunge” and “alternative” market that found favor with the amp’s deep and aggressive sound. Mesa did not intend for bands such as Soundgarden and Tool to use this amp for down tuned riffage the way they did in 1993. They have officially stated they never planned for this amp to redefine a decade of music. However, it is entirely possible they made a wise business decision in altering the amp’s tone to cater to the new market, especially since 80’s shred was in decline. Regardless, a Rectifier will always sound like a Rectifier. It just depends on which flavor you want.

The following snippet from a PremierGuitar.com interview says it best:

            Doug West: "When we first launched the Rectifiers, I would say it was a year and a half before they kicked in. We were actually shooting for the hair bands of the late ‘80s, and we missed that completely and created this new style of amp. We’re currently 16 years into its success."

                 James Egolf: "And that totally turned into the grunge amp."

            Doug West: "Exactly, and that wasn’t even what we were aiming for at all. It’s just this weird thing that happened. Now it’s really appreciated by a lot of the goth and death metal bands, so I think it’s that same thing where you just have to be really patient."
        

 

Much thanks to Edward Morgan and the countless Boogie Board forum members who unknowingly contributed to this document!

©Miguel Massens 2008