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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: 8
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
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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
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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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