scope & tube amp bias quesion

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I just got an oscilloscope.  great to finally be able to properly calibrate all this DIY gear. 

My first project w/ it is to build a dummy load box,  and use the scope to bias some tube amps w/ that method.
What isn't clear to me,  is where would be the best place to put the probes in the dummy load circuit.  I get that the probe would be connected right at the front of the load.  But i'm unclear to where the proper place to put the ground prove would be using this biasing method.

I appreciate any info about this process.

 

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I may have just found the answer to that questions.  found this image.  so the probe to the front of the load,  and the negative clip on the other side of the 8ohm 100w resistor.

If anyone can recommend any tips for this biasing method,  let me know.  will be testing it out when i get the load box build.