Buying a Mark IIB and Lots of Questions

[DC3 Gridlock]

Looks like I am going to buy a Mark IIB Simui-Class. The amp has the EV speaker that I want and the Simul-Class settings.

How well does the 15 watt setting drop volume?

Should I run the amp at 4 ohms at the 15 watt Class A setting?

Can the two EL34's be easily changed out to 6L6's and will the amp need to be rebiased?

I cannot seem to find a users manual for this amp online and am winging it.

I appreciate your help.
Thanks,
Grid

 

[tony777]

I don't have a IIB, but have IIC's, III and a IV.
The class a setting drops volume for some degree, don't know what you have in mind, but it can also be dialed load enough.

You don't need to use the 4ohms output, but experiment if you like. A safe mismatch is always having a speaker with impedance greater, than the output of the amp. Bear in mind that if you use two speakers at 4 ohms and hook them up to both 4 ohms output, the amp will see 2 ohms and is not a safe mismatch.

You can use both 6L6 and EL34 at the outer sockets without rebiasing but you might like to read the quote from the Mark III manual;

NOTE: In the past, MESA/Boogie advertised the "interchangeable power tubes" feature of the Mark III Simul-Class. We told players that they could use either EL-34's or 6L6's in the outer (Class A) power sockets. However, in recent years we've observed a much greater reliability factor with the use of EL-34's in these outer sockets, with much fewer incidents of tube failure. Therefore, today we strongly recommend using EL-34's in the outer sockets and 6L6's in the inner sockets of your Simul-Class Boogie.

 

[DC3 Gridlock]

I don't have a IIB, but have IIC's, III and a IV.
The class a setting drops volume for some degree, don't know what you have in mind, but it can also be dialed load enough.

You don't need to use the 4ohms output, but experiment if you like. A safe mismatch is always having a speaker with impedance greater, than the output of the amp. Bear in mind that if you use two speakers at 4 ohms and hook them up to both 4 ohms output, the amp will see 2 ohms and is not a safe mismatch.

You can use both 6L6 and EL34 at the outer sockets without rebiasing but you might like to read the quote from the Mark III manual;

NOTE: In the past, MESA/Boogie advertised the "interchangeable power tubes" feature of the Mark III Simul-Class. We told players that they could use either EL-34's or 6L6's in the outer (Class A) power sockets. However, in recent years we've observed a much greater reliability factor with the use of EL-34's in these outer sockets, with much fewer incidents of tube failure. Therefore, today we strongly recommend using EL-34's in the outer sockets and 6L6's in the inner sockets of your Simul-Class Boogie.

Thanks for the info Tony, I noticed when I looked at the amp the speaker was plugged into one of the 4 ohm inputs. I am a little worried about how long it has run that way and if it has done any damage to the transformers?

 

[tony777]

Relax!
An 8 ohm speaker plugged into the 4 ohm output is just fine, there will be no damage.

 

[Markedman]

According to the manual, it should be run that way! To quote the Mark llB manual - "Three speaker jacks are provided: one 8 ohm and two 4 ohm. With 60 watts models, plug the single 8 ohm speaker into the 8 ohm jack for the most power and clarity. If two 8 ohm, speakers are used, plug each one into a 4 ohm jack for proper balance. But you may also try other combinations if you want one speaker slightly louder or happen to prefer the tone caused by a slight mismatch; it will do no harm to the amplifier. With 100/60 watt models we recommend that when you run a single 8 ohm speaker you use the 60 watt position and plug into a 4 ohm jack. This will give the strongest possible output without damaging the speaker. You may get more clean power by switching to 100 watts, and still more by also plugging into the 8 ohm jack but remember to avoid lead tone distortion as it increases power dramatically (though not so much the apparent loudness) and may cause speaker damage. With two 8 ohm speakers, one in each 4 ohm jack, the 100 RMS can be safely used."

 

[Markedman]

http://www.mesaboogie.com/manuals/Mark%20IIb.pdf Here's the manual.

 

[DC3 Gridlock]

Thanks guys, good info. I'll keep you posted.

 

[DC3 Gridlock]

Bought the amp. A Boogie owner once again.

 

[DC3 Gridlock]

Got the Mark IIB Thursday evening and am loving the amp so far. I will post a NAD this weekend.

Sure like to get some feed back from member experts on settings for this amp.

Thanks,
Grid