The bias trims on the DSL/TSL amps are VERY different than all of the past Marshall's. Once you remove the back screen cover you will find three gold plated wire prongs poking out from the back of the amp with two bias screws, one on each side. Don't see them? Careful, they'll BITE you! OPEN your eyes! For you combo amp owners you will find these prongs under a black rectangular plastic plug on the back panel.
The center tap is ground and the left tap measures the two left tubes in a 100 watter and the right tap measures the two right tubes and a setting of 80 to 90 DC Milivolts is good. Marshall recommends 90 per side. Don't worry if you temporarily have the bias hotter than 90 while adjusting to a final setting. For instance if both sides are reading at 100 and you turn one side down to 80 the other side will hit about 110 so when you turn this side down, kick it down to about 75 and when you go back to the first side which will probably be at about 100 by now, back it off to about 90 and both sides will probably be very close. After you do this a couple times you will be able to hit it on the first or second adjustment.
In a 50 watter the single tube on each side is adjusted by the respective trim pots and a setting of 40 to 45 is good. Marshall recommends 45 and it's the same scenario, when you adjust one side higher it makes the other side go lower so you have to jockey back and forth to get both sides the same.
Now the biggest question I keep getting is "will I get electrocuted?" Why of course you will! It wouldn't be any fun unless you got electrocuted! So ok, I lied... No, you're dealing with Millivolts here so there is no possible way to get a shock of any kind period. Stop shakin in your boots and bias that amp!
Just clip the black negative lead to the middle prong with the meter set to DC millivolts and then touch the red positive lead to the left prong to test and adjust the left side and repeat by touching the right prong to test and adjust the right side until both read about the same as explained above. This is done with the amp on and in the play mode with a speaker load on the amp. This does not mean that you set a speaker cab on top of the amp to put a load on it, it means plug a speaker cab into the amp!!!
Now that you have read about biasing a 2000 series amp you ca watch a video about it here!
http://www.eurotubes.com/euro-video.htm
The bias trim on the TSL 60 is very different and much simpler to adjust than the DSL/TSL 50's and 100's which have two trim pots. The center tap on the TSL 60 is ground and the left tap measures the left tube and the right tube and a setting of 80 millivolts is good. Just set your multimeter to DC millivolts and dial in the tubes.
You guys with 201 and 401 amps have to take the amp apart to get the test points and trim pot. Here is a pic. Marshall recommends a setting of .675 volts for the 201 and 1.375 volts for the 401, I feel that the 1.375 is way too hot and recommend a setting of between .8 to 1 volt if you are using the test point and for the 201 .375 to .400 to .500 is good.
