Half/Full power switch on Mesa Mark III green stripe head ?

[asookazian]

I recently acquired a used Mesa Mark III green stripe head that sounds phenomenal (and I have a Marshall JCM 800 2205 and Mesa RK to compare this head too!).

The user manual I downloaded from Mesa web site only shows the model with the half/full power or class A/simul-class switch ON THE BACK OF THE HEAD. Mine has a half/full power switch ON THE FRONT OF THE HEAD, next to the standby and EQ switches. It is labeled Half (below switch) and Full (above switch). There is no switch on the front or back of the amp labeled "Class A".

One person on here posted me back earlier and said that I have the medium chassis, the manual is only referring to the short chassis. There is a simul-class sticker on the back of the amp. I called Petaluma and the tech there said the only way to know is to check the side(s) of the transformers and see if there is a simul-class sticker. I didn't see any sticker(s) as such but did not remove the amp chassis from the head cab to view from all angles.

Somebody else on here stated that all Mesa Mark III's are simul-class. I don't believe that b/c in the manual (page 5 of the online PDF version) it states the following:

"This is the 'Class A/Simul-Class' switch or the '60/100' switch, depending on amplifier type."

So my question is................

Is my green stripe amp a Simul-Class or not? In other words, when I switch to half-power on the front of the amp, is the head now in 60watts or Class A (only the outer-EL34 tubes are in use)? If it's in Class A, is it in 15 watts now? And then how many watts in full power mode?

I have a feeling half-power mode is Class A b/c it sounds completely different than in full power or my Marshall JCM 800 which is running two EL34's as well. Has very nice violin-like sustain in half-power mode. And sounds like a giant killer in full power when cranked to 5 on masters.

Any feedback would be appreciated.

thx.

 

[Paul Secondino]

here's a similar thread that might help you

http://forum.grailtone.com/viewtopic.php?t=8757

 

[asookazian]

yeah thx. I read those responses after I posted that.

Guess that means half-power = Class A (15 watts???) I honestly don't know how many watts this head runs at in Class A and simul-class. I'm guessing 15 and 85 but not sure. Mark IV with four 6L6 is advertised as 85 watts on the Boogie web site.

Although Mesa does a very good job on amp documentation (much better than Marshall, for example), there is some room for improvement. This Mark III situation is a good example. Also had to call their tech support in Petaluma to find out the purposes of all five 12AX7 preamp tubes in the RoadKing b/c it's not in the 50+ page user's manual. That seems pretty basic stuff that's missing...

 

[Paul Secondino]

The best thing to do is pull the chassis and check the tranny. It's not hard to do and isn't dangerous. UNscrew the 4 screws on top of the head and the chassis is ready to come out. Jsut pull it out slowly and remember to disconnect the fan so that you don't stress the connection. You aren't in danger of being shocked until you start touching the contacts on the PCB or on the transformer itself.

 

[Boogiebabies]

There is no sticker on the OT. At the advent of the green stripe it is the simul-class 562004 like from the MK IV. If the amp is a MK III green stripe it is a simul-class. The sticker on the left rear is proof.

 

[asookazian]

I saw some info engraved on the top of the tranny (looking from behind, back left -- OT??) It's hard to read b/c of angle but I will check for that model # again. Thanks for the info.

 

[asookazian]

here's a link about another green stripe and id'ing it:

http://www.grailtone.com/forum/viewtopic.php?t=2174&view=next

 

[Boogiebabies]

I saw some info engraved on the top of the tranny (looking from behind, back left -- OT??) It's hard to read b/c of angle but I will check for that model # again. Thanks for the info.

The back left is the power transformer. You need the one on the right.

IT IS A SIMUL-CLASS.........

 

[Guitarzan]

I saw some info engraved on the top of the tranny (looking from behind, back left -- OT??) It's hard to read b/c of angle but I will check for that model # again. Thanks for the info.

The back left is the power transformer. You need the one on the right.

IT IS A SIMUL-CLASS.........

Wow, 3 posts in a row. can we say that you're back? Good to see you BB!

 

[Boogiebabies]

Hey GZ,

I'm just trying with all of my heart to say " It's a Simul-Class" !!!!

Now I feel better.

Of course I am at work and I had a little down time.
It's good to contribute to this place every once in a while.

I also wrote a manifesto on the IIC+ and it's bias.

 

[asookazian]

OK cool. The half-power (Class A) mode is killer for Gilmour style blues in lead channel. Great sustain and juicy tone with an Epi Elitist Les Paul.