How to bias a tube amp with a Multimeter

Yes, probes are properly connected. 
 

I was just quoted $130 to bias the amplifier. But I’d have to wait 4 weeks to have it done because of other jobs ahead of me! Argh. 

Paying to have the amp biased won't help you in the future..For that much $ I would want at least a diagnostic of the test point problem included..
 In the mean time,I would run the amp & see how it sounds..If it was properly biased before going into storage,there's no reason to think it's drifted off much..
I might also consider buying another meter,I mean $20.00 for another meter that can be returned is a lot faster & cheaper than the alternative..Good luck..

@freediver excellent points all around. I requested a later tech I contacted that I’d need to be instructed how to bias the amp from the bias points. He accepted that. 
 

Since I don’t have a manual, and haven’t found a pdf on the internet I’m kind of at the mercy of someone who has knowledge. I’ve been running the amplifier for several hours without any runaway tubes, but don’t won’t to run the risk of having that happen, and simply operating the amp without knowing the status of the current bias seems a bit foolish. 

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.