Mark III bias

Mark I's, II's, III's and the almight IV

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Bottle Rocket
Posts: 19
Joined: Mon Apr 25, 2011 5:53 pm
Location: Chicago

Mark III bias

Post by notune » Sat Aug 31, 2019 6:10 pm

I have a mark iii blue stripe simulclass, I'm running EL34's in the outer sockets and I tried a few different pairs and there all running cold 10 to 16ma. It had Mesa branded El34's and those where 14ma Grey code.I tried some 6L6's and they where 46ma so i'm guessing the bias supply is working correctly it also sounded really good. I have had amps in the past that I would have to change a resistor so the bias pot would adjust to get the tubes in operating range. The outer tubes have a 1/2 resistor from pin 1 and 5 would that be what i need to change.

Mark II
Posts: 138
Joined: Tue Oct 11, 2011 4:36 am
Location: Austria

Re: Mark III bias

Post by TiPiMods » Sat Oct 19, 2019 11:36 am

Which stripe is yours? try to find the right tubes, that fit. Dont change the bias. In my red stripe simul I run JJ EL34 in the outer sockets which run quite hot. Dont know if they changend the bias setting in the different stripes, only know the green stripes run on pentode operation in class A sockets, wheras the older Mk IIIs run in triode mode on the class A sockets. I always order the hottest tubes with the strongest emitting I can find for my Boogies because they traditionally run quite cold in the AB sockets. With the outer pair you have to experiment. Anyway it's not real class A but rather a hotter class AB, so try not to get too hot.
Mesa Boogie MkIIB, MkIII red stripe, Caliber 22+, Studio Preamp

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