[old_tv_nut]

I re-read the Gun Balance section fo the Super Mack manual, and I think the criterion for "good" is poorly written. It says:
"A tube that fails to adjust TO the GUN BAL line should be consdered questionsable..."

It doesn't say from which side it should adjust TO the line. I'm thinking that the tube has too little gainl if it draws too much current and reads to the right of the line, but if it reads lower (or zero) the gun has higher gain than minimum acceptable and is OK *at least for a B&W tube) - just out of spec in a good direction. Of course, if you are looking at a color tube, it's more important that all three guns are similar, and you need SOME current on all three to see if they are equal.

Just for yuks, I would take the tube that tests good on the B&K, put it on the Mack, and try the next (less negative) bias setting if there is one, to see if the GUN BAL control can show a usable meter reading with less negative bias.