How to bias a tube amp with a Multimeter

To be clear, I recommended trying to screw the test points, which have indentations for a blade-type screw driver; I was NOT talking about the adjustment pots.

Most bias adjustments are measured in milliamps, not millivolts. When you adjust the bias pot, you are changing the bias voltage, but, typically, you measure the current flowing which is milliamps.  Could it be that you are trying to measure the wrong thing?

Also, if you have a tech doing the adjustment, you might want to know how he determined the correct range for adjustment.  This depends on the design of the amp, so there is no single value that works well for all amps.

@larryi okay, so how do I set the multi meter to display Milliamps? No, I didn’t turn what appears to be the small screws. Are you suggesting to turn the screws while hoping the MM on them at the same time? If that’s the case, what of the larger outside screws?

That’s what I thought was the way to raise or lower the voltage.

I know from several owners of the S8Mk that it’s correct bias point should be between 35-40.

Sorry, an electronics technician I am not. In fact, I’ve never attempted to bias any tube amp that didn’t possess a meter and a clearly defined bias switch to determine which tube I was trying to adjust. With no manual I’m flying in the dark with this amp.

I thought that turning the screw would create a contact that would activate the probe point.  Your amp otherwise does not appear to have a switch to activate bias testing.  I could not think of any other reason why the test point has a groove that makes it appear to be a flat head screws.  

The picture you have of your VOM has, for the selector knob, 40A and 400A, which I assume is not 40 or 400 amps (crazy high current), but is 40 and 400 milliamps.  Select 400A and try testing, if the needle barely moves, then select 40A.  

^^^ Thinking about what he's saying..Try backing one of the + screws out & see if it comes all the way out or has a stop point..If it has a stop point move the ground screw out as well & retest,you never know...

@larryi @freediver thanks for your suggestions. I will try adjusting the MM, and the screws on the amplifier tomorrow to see if I can get a reading. Thanks for your assistance!