Output tubes for ARC Ref 110

One more question but regarding output tubes and bias.
My amp came with 6550 and the manual says to set the bias to about 65mA
Now that I have KT120 - do I still adjust to the same bias of 65mA or should it be adjusted to a different value ?

 Yes, bias them the same at 65ma. The KT 120s should last much longer than 6550s. I have heard around 4000 in the Ref 110.

OK....so just finished replacing the tubes and re-adjusting the bias.
The instructions say to adjust bias at the V5 tube to 65mVDC and then measure V7 to make sure it falls between 55 and 75 mVDC and do the same for other pairs.....

What I noticed is that  the mVDC at the main tube in the pair is showing as positive number (always 65mVDC) but when I check the voltage at the slave tube - I get negative reading...( ex: -60mVDC)
I was able to adjust the tubes and everything is as it should except for that reverse voltage for every slave in the pair.... I made sure I am not reversing the probes....
The manual doesn't say anything so I am just surprised.....