Originally Posted by steelhorse

I think Bob realized that with the bias probes and the multimeter setup he used he probably confused a few folks but it's really simple with the DSL100.

All you need is a decent multimeter. I ordered mine form Euro Tubes.

Take the multimeter and set the dial to the 9:00 position which will be in the DCV 200m setting.

Take the black lead and plug that into the COM port at the bottom right side of the meter.

Take the red lead and plug it into the DC port

I have alligator clip adapters so I use one on the black lead which I clip on to the ground post on the amp bias adjustment.

You'll be using the red lead for the readings.

Be sure the amp has been on for a few minutes to get plenty hot on standby.

Take the amp OFF standby like you are going to play.

Take the red lead and touch each test point on the bias adjustment of the DSL to see where you're at.

We're looking for a reading of between 80 and 90 mV.

With an insulated or plastic small head Phillips screwdriver make MINUTE adjustments to 1 side at a time (you'll see what I mean when you adjust yours!). Remember when you make one side hotter it will cool the opposite side down some, so it will be a back and forth venture until the see-saw quits and you get near identical readings on both sides.

I set mine to 86mV. Played with it for a few days, and went back and checked it for drift but it was still very close so I left it.

The things that could make it easier is of course getting another multimeter, clipping both grounds to the ground post and the positive lead of each to one test point so all you need to do is watch the meters while making the adjustment but it's really simple to accomplish the same thing with only 1 meter, it just takes a little time and patience.

I recently read on the Euro site that the factory test points on the JSX heads are unreliable and they had steps to follow to bias it properly. With that head I switched the meter to the 4:00 position (DCA) moved my red lead to the mA port and used a bias probe on 1 of the tubes (it needs to be a matched set to do it this way). It took some time but with the JSX you just adjust the little dial to get the bias set.

Hope this helps!