[ARC5] Tube Question

[Robert Eleazer]

I finally got out the tube tester I bought a while back and stared learning how to use it.  It is simple emission tester. 

I found something puzzling.  I have two 6AW8A tubes that were sold to me as good and a 6AN8A tube still in its original military box; these are basically the same type tube.

In the tube tester all three test as bad, the meter needle in the high area of the "replace" range.  Also, the meter needle wavers.  However a slight upward adjustment to the Shunt control shows the tubes as good.  This is true for both sections of the tubes.

Anyone have any ideas on this?

Thanks,

Wayne