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NAD! Mesa Boogie Mark III Simul-Class: Help & Suggestions Needed


buddhapaugh

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My new to me Mark III Simul-Class head arrived today. The guy said it was blowing fuses. No fuse in it when it arrived. Tubes are Mesa Boogie---4 6L6's--and appear to be in good shape cosmetically. The thing that concerns me is that there is considerable rust on the OT (came from the moisture drenched Pacific Northwest).... and I seem to recall someone saying that any rust that gets between the laminates of the OT can result in fuses being blown.

 

The good news is it is Blue Stripe.... which apparently is one of the more highly thought of Mark III's.:thu:

 

Also, with the Simul-Class is there a problem running all 6L6 power tubes. I thought it was meant to have EL34's in the inner sockets and 6L6's in the outer sockets?

 

Further, can someone fill me in on biasing the amp. I have done biasing before and have the equipment to do so. I am just curious about how best to approach it and where the bias trim pot might be located, and what the appropriate bias range is for the Mark III.

 

Thanks for any input... I really appreciate it. :lol:

 

PICT0260.jpg

 

PICT0265.jpg

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Further, can someone fill me in on biasing the amp. I have done biasing before and have the equipment to do so. I am just curious about how best to approach it and where the bias trim pot might be located, and what the appropriate bias range is for the Mark III.

 

Mesa amps have non-adjustable fixed bias. Unless your amp has been modified, there is no reason to mess with the bias setting.

Buy new Mesa-brand tubes (or the recommended equivalent from a reputable source), put hem in the amp, and :rawk:

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Thanks for all the input. You guys are great!:thu:

 

On closer examination---and you may be able to see from the pics--the rust appears to be on the PT and not the OT. It actually looks like it may have a new OT... and that the OT has been dipped in varnish.

 

All preamp tubes are also Mesa. I have some Svetlana 6L6GC's laying around and some Electro-Harmonix EL34's. I am assuming I can just pop them in there with a new fuse and give it a whirl.... right?

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No - the tubes that you have aren't guaranteed to be within the correct range, because (I'm assuming) that they weren't tested and sold as "Mesa-spec". They will probably work but the probability that they're in the correct bias range is low.

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Just popped a spare 3A 250V fuse in, replaced the 4 power tubes and fired it up.... Uhm.... WOW! This is going to be a fun amp!:love:

 

I also downloaded the manual for the Mark III since there are so many features and all of the different functions seem to be so interactive. I don't have my full rig here at home so it will take rehearsal Friday night to truly see what this baby can do for me. Right now I am just running through an old ADA 2-12 cab loaded with Celestions... so far so good!:thu:

 

If any one has any more suggestions or input I would greatly appreciate it.

 

Thanks.

 

P.S. Considering it is old, well-used, and was in need of some new power tubes I am thinking $600 for it was a pretty good deal!:lol:

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Thanks man! You were one of the ones who steered me to it when I was asking which Mesa to buy!:thu:

 

I am SO glad I listened to you and others. It is perfect for me. I can't wait to tweak it further and really dial it in at rehearsal.

 

I am noticing if you keep the Bass down it is so articulate and clear. I don't know if I have ever heard such TIGHT GAIN on an amp. It's not fizzy or muddy at all (and so many amps are fizzy or muddy when you turn up the gain/drive).

 

Thanks again! By the way, anything ever happen with the Michigan Amp Meetup??

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Well..... for whatever reason I cannot get anything out of the Lead Drive and Lead Master controls.... they are effectively dead.... there is no change in volume or gain when turning them.... and yet I can engage the Lead channel with a footswitch and when Auto EQ is also engaged there is a jump in volume due to the 5 band Graphic being turned on.

 

I tried changing V3 to no avail.... not sure what to try next. Bad pots?? They don't even scratch or hiss when I turn them.... nothing.

 

Any help out there??:cry:

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YOu got the amp for a good price. Take it to someone who know what they are going. Even if it cost's you $200, it's money well spent for a solid amp. Don't {censored} it up by continuing to play it
broken
.

 

Yeah, you are probably right. I did what I could by putting in some different preamp tubes. It's just that the 2 channels I have sound so damn good I want to play it!!:lol:

 

I won't be ampless so I suppose I'll haul into someone and have them give it a look. Maybe I'll pull the chassis out myself and see if anything stands out to me. I like taking stuff apart... I always learn something new that way!:lol:

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Maybe I'll pull the chassis out myself and see if anything stands out to me. I like taking stuff apart... I always learn something new that way!
:lol:

 

Be careful of the big blue caps inside the chassis. These can easily kill you if you touch them. I would take it to a qualified tech in your area. Call Mesa and they can send you to the nearest shop that can give your amp a "once over" and see if there are any repairs that need to be met.

 

Also, make sure that the fuse that you used in the amp is EXACTLY what the amp calls for.

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Thanks. I used a specified fuse... amp sounds great and exhibits no signs of distress... no noise or microphonics... or pot issues other than the lead channel controls don't do a damn thing!

 

I'll make some calls tomorrow and see if I can find someone to look at. May have to ship it.... oh well... I'll feel better knowing it has been gone over with a fine-tooth comb.:thu:

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