[dconant]

I'm pretty sure I understand now. I watched an Uncle Doug YouTube video that helped explain this in dummy terms. https://www.youtube.com/watch?v=5jUitplchok I would hate to do all that measuring with my transformer. So if I use the plate load impedance of PP 42 tubes at 10K and a voice coil of 1.5 ohms I could just use the chart I posted earlier that would tell me to use the 4&5 connection. If I used the PM speaker with voice coil at 5.3 ohms I could use the 6 ohm column and find the nearest row to 10K. If that is so I don't need all that arithmetic?

Please if you would tell me what happens when the match is not perfect.

Just to help me understand a little more about the 42 tube, is my radio class A or AB?