[klondike98]

Someone else should check me on this but the full service bulletin #326 that you can find here (you need the djvu reader to see it) says the output meter should measure the AC voltage across the screen grid and plate of the 41 output tube.  That would be pins 2 & 3.  Those pins drive the primary of the output transformer so you could also connect to a point where the black and white wires of the transformer connect if its not at the tube pins (if there is an spot to do so...I've not worked on one of these).  I believe the adapter just allows you to put the tube in place and access pins 2&3 from on top of the set.