I know a little late to the party, about the W.E. 300B testing But I was looking for setting for a 2A3 and came across this forum!
We have an older Precision Apparatus 920 with many older tube chart sheets (all older) that did not have setting for the 2A3
However our supplementary tube charts do have the settings for the 300B
Possibly to help someone else for future reference
On a Precision Apparatus 920 settings:
for a 300B are A-3, B-5, C-40, D-4, E-1, F-1, Press B