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PostPosted: Tue Jul 10, 2018 6:31 pm 
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Bottle Rocket

Joined: Mon Dec 14, 2015 8:19 pm
Posts: 13
So I sent my Mk3 to boogie to get some major work on it done and found out that it’s not a simul class even though it was labeled a simul class. So my question is, has anyone had a none simul class modded to a simul class or is it even possible?


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PostPosted: Tue Jul 10, 2018 9:21 pm 
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Donating Member
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Location: Norfolk, CT
I have heard of it, you can search here on the BB and you'll find something like this - viewtopic.php?f=3&t=71308&hilit=simul+class+mod

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PostPosted: Wed Jul 11, 2018 10:50 am 
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Bottle Rocket

Joined: Mon Dec 14, 2015 8:19 pm
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Wow lots of info in that thread, I think a call to Boogie is in order. Thanks!!


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PostPosted: Wed Jul 11, 2018 11:49 am 
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Mark II

Joined: Fri May 04, 2018 10:36 pm
Posts: 90
I've been doing some reading on simulclass. It took some time to find the information and read it and digest it. Sorry we didn't have any answers for you within 15 minutes.


There are those who have dissected output transformers from simul-class amps and found that there's nothing different about them vs. the "regular" variety output transformer from a non-simul-class amp. But I don't know if that's ALWAYS the case.

However, if it IS, then all that's really happening is that the outer two tube sockets have added resistors that function as a voltage divider on the cathodes, to change the bias points on the outer tubes so they run closer to class A.

BUT....there are multiple schemes Mesa has used. It may be that there ARE different output transformers, and I tend to think that there actually are, since simply rebiasing the tube to run in class A means it's going to run a lot hotter. Unless you reduce current which requires reducing plate voltage, which would require a different wind on the output transformer.


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PostPosted: Wed Jul 11, 2018 12:19 pm 
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Mark IV
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Joined: Wed Sep 08, 2010 4:12 pm
Posts: 664
Location: Petaluma, California
woodbutcher65 wrote:
I've been doing some reading on simulclass. It took some time to find the information and read it and digest it. Sorry we didn't have any answers for you within 15 minutes.


There are those who have dissected output transformers from simul-class amps and found that there's nothing different about them vs. the "regular" variety output transformer from a non-simul-class amp. But I don't know if that's ALWAYS the case.

However, if it IS, then all that's really happening is that the outer two tube sockets have added resistors that function as a voltage divider on the cathodes, to change the bias points on the outer tubes so they run closer to class A.

BUT....there are multiple schemes Mesa has used. It may be that there ARE different output transformers, and I tend to think that there actually are, since simply rebiasing the tube to run in class A means it's going to run a lot hotter. Unless you reduce current which requires reducing plate voltage, which would require a different wind on the output transformer.


This requires a different transformer, and more.

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PostPosted: Mon Jul 30, 2018 8:58 pm 
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Bottle Rocket

Joined: Mon Dec 14, 2015 8:19 pm
Posts: 13
Well I called and confirmed that it can be done so no worries there.


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PostPosted: Mon Aug 06, 2018 2:42 pm 
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Mark II

Joined: Fri May 04, 2018 10:36 pm
Posts: 90
Before you send your amp in for that work, please make a note of the part numbers on your transformers. Then when the amp has come back after the upgrade, check the part numbers on the transformers again.

If you really feel frisky, remove the chassis and make good detailed photos of it before and after the surgery, too, so we can see what's really getting changed.


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PostPosted: Mon Aug 06, 2018 3:16 pm 
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Mark III

Joined: Sun Aug 21, 2016 5:23 pm
Posts: 221
Location: Hardwood Heaven
woodbutcher65 wrote:
Before you send your amp in for that work, please make a note of the part numbers on your transformers. Then when the amp has come back after the upgrade, check the part numbers on the transformers again.


My Mark I was converted to simul-class at Mesa and I can confirm the output transformer was swapped.

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