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Based on my reading of the Mark III schematics on the web, the R2 channel does not cascade any additional gain stages relative to the R1 channel. Instead, it utilizes more of the gain that is inherently available in the R1 circuit, but which is simply not used in the R1 setup. For example, the...

The Mark I is quite different from the other Marks. If we're talking about the lead channel (and what else would we be talking about :wink: ), the architecture of the Mark I is totally different...its lead circuit is pre-EQ, rather than post-EQ like on the Mark II/III/IV. Therefore, from a...

Whoa, whoa, whoa. Ease up a little here...let's not get to crazy with too many conclusions all at once :wink: It is true that the non-lead portions of the pre-amp in the Mark series is derived from the classic blackface Fender pre-amp. It is true that pulling the "Pull Bright" and the "Pull...

Ah, I had not noticed C30 going to ground. Very good! Thank you for pointing it out.

Thanks so much for this! I don't own a Mark III (I have a Mark IIC that was upgraded to a IIC+), but I've always been curious about the circuit differences between the various Mark III stripes. If I may request, could you also trace out the power amp...especially the presence circuit (which is...

I have a Mark IIC(+) and a 65 Fender Deluxe Reverb Reissue. The cleans do feel quite a bit different, so I totally agree with you there. But, on the narrow issue of the circuit that implements the tone stack (the Treb, Bass, and Mid knobs), it turns out that the Boogie and the Fender are built...

Regarding the hypothetical mod to turn a Simul-Class into a 60/100... To go the other way -- to turn a 60/100 into a Simul-Class -- they have to put in a new output transformer. I can only presume that to go from Simul to 60/100 they'd also need to swap the transformer. That's not cheap. You...

I have a deluxe reverb re-issue and a Mark IIC+ (not a Mark IV). In my opinion, the Fender and Boogie are quite a bit different sounding and, most importantly for the player, they are vastly different *feeling* when you're playing them. Still, if you are gonna give it a try, I'd recommend the...

IIRC, for Channel 3 on the Mark V, the circuit is built as if "Volume 1" were hard-wired to 7.75. So, its function in the circuit is there in the Mark V...it's just not changeable by the user to adapt to different styles or guitars. Chip

If you're looking at the 30 uF caps and the 220 uF caps, I think that you're looking in the wrong place to tame your perception of too much bass. As suggested above, look at reducing the value of the caps on the cathode of each pre-amp tube, or reducing the value of the caps between each...

I popped open the Mark V schematic to see what they were doing about the "Pull Deep" functionality and to see how it compares to its implementation on the IIC+. On the IIC+, the Pull Deep enables a big fat cap on the cathode of the tube immediately following the reverb and effects loop (V2B)...

Do you know that the circuit is designed to mimic the not-pulled-deep mode? Or are you just saying that there's no switch? There's no Mark V switch for the equivalent of the pull-bright on the Mark II/III volume knob, yet it's built into the circuit. The same could be true of the Pull Deep...

One important driver of the brightness of these amps is the Presence knob. The voicing of the Presence circuit (IIRC) is quite different on the Mark III vs the Mark IIC+. I don't own a Mark III myself, but I've heard comments like "Presence of 7 on my IIC+ is like a zero on my Mark III"...

Don't confuse your bright switches. Yes, there are two. One is engaged by pulling the Volume knob (the one on the far left of the Mark II and III), which affects both the clean channel and the lead channel. The other is engaged by pulling the Lead Master knob (the one on the far right of the...

Hey George. Gonna disagree with you here. As much as I love the clean channel on my IIC(+), it's different than a Fender. Anyone who's deep in love with a Twin Reverb should not expect to find that sound in the Mark IIC...because, if they expect to find it, they're gonna be disappointed...

I've got a IIC+ open-backed combo with an EVM12L. I also have a Mesa Thiele that came with an EVM12L. A couple years ago (when the IIC+ was fairly new to me), I tried a few different speakers in the combo and in the Thiele, including a V30. I agree that the EVM and the V30 sound VERY...

I spent some time A/B'ing my Boogie with a few different speakers. My Boogie is a IIC->IIC+ conversion. It's a 60/100 not simulclass, so there's some difference there. In my opinion, in the open-back 1x12 combo, the EVM12L is definitely superior to the V30 for the IIC+. Absolutely no...

I have an IIC->IIC+ upgrade that was done by MB sometime around 2009-2010 (I can't remember...time passess so quickly). He seemed to be a pretty decent and direct guy. In addition to doing the usual IIC+ upgrade, he also suggested that my amp needed a fix/replacement of the reverb tank and...

I didn't know that about the later ones. I also never really understood what that cap was doing. I went back and forth. One option was "it must be introducing a high-frequency roll-off", but if so, why not just send it to ground instead of to the cathode. I guess it could be a partial...

In terms of numbers, there are so few IIC+ because they were not in production for very long. In terms of numbers, yes there are a couple thousand made over a couple of years. That might not sound like many amps, but Mesa was a boutique manufacturer back then...not at all like now. For...