Help with a MK IIC+ lead channel

I just picked up a Mark IIC+ head and I'm having some issues with the lead channel. With the volumes cranked and the lead channel engaged, I'm hearing the pre-amp gain with the lead master way down. As I turn the lead master up, it seems to blend with the clean channel; it sounds cleaner and cleaner the higher up I turn the lead master and with the lead master way down, it sounds like a crappy fuzz pedal. Most of the pots are pretty scratchy and I can tell the amp was played a bunch. It needs some servicing for sure but does anyone have any idea what might be the issue with the lead channel? Could it be a bad preamp tube? Which preamp tubes should I check? The clean channel works fine and sounds awesome. I'm looking for the liquid leads though, and I'm not getting them at the moment.

BTW, it is a factory C+, long chassis with GEQ and reverb. Not sure if it's simulclass but I'll find out when I pull the chassis this weekend. Another cool thing about this amp is that it has Randall Smith's initials on back instead of Mike B's. It was a once in a lifetime find. I have no issue paying for a tech visit, but was hoping it might be something I can address quickly just to check out the lead channel. Thanks in advance!

Where's your Lead Drive at?

Try setting it up this way: http://www.chain-metal.nl/mark3/front.php?bg=0&t=Metallica+-+Master+of+Puppets&p=45&d1=90&d2=70&d3=15&d4=40&d5=45&d6=70&d7=50&p1=&p2=1&p3=&p4=&p5=1&p6=1&p7=&g1=55&g2=50&g3=10&g4=40&g5=55

If that doesn't get you a loud distorted tone, then there is a bigger issue...Careful as that setting is very loud. If you can't figure it out this weekend, call Mesa factory Monday morning and try talking to Mike B.

Careful as that setting is very loud

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Dude, that's setting is VERY LOUD indeed! My settings are similar only the master is at 1.5 and it's super loud, and I have a sixty watt C+. Come to think of it, I have never even heard my amp above 3.5 it's that loud. (I don't actually remember turning it up that loud, but I probably did on the first day I owned it just to do it, but never above 1.5 at practice or at a gig.)

beng2040 said:

As I turn the lead master up, it seems to blend with the clean channel; it sounds cleaner and cleaner the higher up I turn the lead master and with the lead master way down, it sounds like a crappy fuzz pedal.

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It doesn't sound like a tube problem to me, more like some shortage to ground. Anyway for a tube check, Replace one tube at the time to see if there is any difference. Otherwise if you're in the US, send it to Mesa for a full checkup and service, it might cost you some, but in the long run it will definitely be worth it. Great find of one of the worlds most sought after amps regardless if its a 100 or simul.

Thanks guys. I swapped preamp tubes out with no luck. Took it to my tech and he's already done with it. He said that two LDR's in the switching circuit were bad as well as the plate load and cathode resistors on the gain stage. He also said it is not simulclass and only runs on 6L6's. I do have the original factory tag that says it's a DRG model though, which I thought meant it was simulclass. He could be wrong but he has a MKIIC that is simulclass so he is pretty familiar with these amps. He's a great amp tech too (one day turnaround!). Regardless, the clean channel on the amp sounded so great that I don't care if it's simulclass or not. I can't wait to get it today to check out the gain channel now that it's fixed.

Question for you all, I need to buy new power tubes for this amp as it's currently loaded with an unmatched set. Should I stick with Mesa 6L6's or should I go NOS? Thanks.

Glad it got fixed!

I would recommend reading this post: http://forum.grailtone.com/viewtopic.php?f=27&t=18184 and check for the codes on your transformer to confirm Simul-Class or not.

As for tubes, Mesa tubes obviously work well to give you a base sound. From there you can begin to experiment. If you have the $$, look for the STR 415 that the amp originally came with.

Elpelotero said:

Glad it got fixed!

I would recommend reading this post: http://forum.grailtone.com/viewtopic.php?f=27&t=18184 and check for the codes on your transformer to confirm Simul-Class or not.

As for tubes, Mesa tubes obviously work well to give you a base sound. From there you can begin to experiment. If you have the $$, look for the STR 415 that the amp originally came with.

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Thanks! From what I can see (without pulling the chassis) mine has a simul-class OT. I can make out the "simul-class" imprint on the OT. Does that mean that mine is SC? My tech said it wasn't, but as good as he is, I'm not sure. I have the original tag from the amp that says it's a DRG model. I want to put some EL34's in there but I don't want to mess up my amp if it is indeed a 60/100. Is there any other way to be sure, short of pulling the chassis? I'm not very tech oriented but can pull the chassis if needed, though I'd like to figure it out without having to do so if possible. Regardless, this amp sounds awesome!

If your output transformer reads something like "SC-152019B" then it's a Simul-class.

In this picture you can see that pins 3 and 4 are connected in a Simulclass Mark series amp by the big brown resistor. I think that you can use a multimeter set to continuity to probe the outer sockets to verify if these two pins are connected with the chassis in the shell. If you look at the socket to the left of it, you will see the normal 60/100 wiring pattern.

Thanks guys! I pulled the chassis (much easier to take out/put back in than a Fender) and it's definitely a Simul-class. So, I have a factory Mark IIC+ DRG with Randal Smith's initials. Score! I love this amp! Can't wait to try some EL34's in it.

Here it is: