Mesa Boogie Mark III Simul-Class modded to be non simul

[Jordan1990]

No telling why it was modded.I have never modded an amp as you describe,but I have done an adjustable bias mod to a few MkIV simuls and I can tell you its a royal pain in the ass.It becomes more of a compromise bias control since there are different voltages going to the inner pair and the outer pair of power tubes,get the inner pair biased where you want and the outer pair may be too hot,so if someone wanted to set up the 4 power tubes to run "balanced" I could see doing it,but it might be more work than someone would want to do.I am not a fan of simul,for numerous reasons,so if I owned a simul amp,I might mod it,but I wouldnt buy a simul amp to begin with.
Could also be that the amp had a bad OT and someone replaced it with a standard OT.Who knows,wait til you get it and see just what someone did.Oh,and just FYI,"60/100" isnt necessarilly "simul".

Say this was modded to be non simul. Would I get 15/75 watts or whatever the non green stripes are

 

[JOEY B.]

Ok guys wait is over. I hope everybody sees this so I won't have to quote everything. I got the amp and barely saw it has a Simul-Class OT. When I got home from work I yanked it out of the headshell and the inner tubes pin 8 are connected together and running to the half power switch on the front. And pins 3 on the inner tubes are goin to the OT that says Simul-Class. So WTF lol.

The pin #8 thing is normal and correct for a 60/100 or Simul-Class. The thing to check is does it have different wires at pin #3 of the inner or outer tubes connected to the output transformer. The resistors from pin #5 will be the same value on a 60/100, but much different on a Simul-Class model. If this adds to the confusion, I am sorry.

 

[Jordan1990]

Ok guys wait is over. I hope everybody sees this so I won't have to quote everything. I got the amp and barely saw it has a Simul-Class OT. When I got home from work I yanked it out of the headshell and the inner tubes pin 8 are connected together and running to the half power switch on the front. And pins 3 on the inner tubes are goin to the OT that says Simul-Class. So WTF lol.

The pin #8 thing is normal and correct for a 60/100 or Simul-Class. The thing to check is does it have different wires at pin #3 of the inner or outer tubes connected to the output transformer. The resistors from pin #5 will be the same value on a 60/100, but much different on a Simul-Class model. If this adds to the confusion, I am sorry.

[email protected] is my email address contact me here so I can take some pictures tonight and get them to whoever wants to help. I can't figure out how to on a phone on the forum

 

[Jordan1990]

Ok looking from the back of the amp the two tube close to the Simul-Class OT have orange or red wires to them and one has a white line the outer one actually. The other 2 tubes have blue with the outer that had a white line on it. All connected to pin 3 and going to the Simul-Class OT. Pin 5 on outer tunes jumps over to pin 1 and 8 and then goes to pin 5 to the inner tube. What I think to be a resistor is purple on the outer tubes and a light blue on the inner.

 

[Jordan1990]

Please excuse my ignorance of what everybody is talking about. This is my first rube amp and I don't mind 60/100 I just want to make sure

 

[stokes]

I dont think anybody can know for sure what went on in any mod from where we sit.As I said earlier,simul is more than the "class A/simul class switch" on the cathodes.The plates are wired as I described earlier,but if you look at the schem,the outer tubes have the screen and plate connected to make a lower powered "triode connected" tube.The inner pair have the screens connected to a seperate B+ rail tap.We need to know more than "pin 3 has a blue wire..." we need to know whee these connections go.

 

[Jordan1990]

I don't know if this means anything but when amp is turned on all tube glow light red or orange when standby is off they have a blue color to them and when half power switch is down the two inner tubes lose the blue

 

[JOEY B.]

I don't know if this means anything but when amp is turned on all tube glow light red or orange when standby is off they have a blue color to them and when half power switch is down the two inner tubes lose the blue

This happens on a 60/100 and a Simul-Class amp, that is why the two inner tubes are tied toether at pin #8. The switch lifts the ground from those tubes.

 

[Jordan1990]

I don't know if this means anything but when amp is turned on all tube glow light red or orange when standby is off they have a blue color to them and when half power switch is down the two inner tubes lose the blue

This happens on a 60/100 and a Simul-Class amp, that is why the two inner tubes are tied toether at pin #8. The switch lifts the ground from those tubes.

Oh ok thanks for the quick reply. I'm just gonna take it somewhere and have it looked at. I found a guy who seems to know a little about boogies about a hour away from me. I did find the amp on reverb when the owner before the owner I bought it from was selling it and he had all his pictures with the el34 tubes that came with the amp in it and talked like it worked great. I'm finally getting a cab tomorrow so I'll be able to see of there is a noticeable drop in volume with it. It's at a friends venue so I can crank it up and try this beast for the first time