When calculating the (max) power supply needed for an tube amp and using the formula

V(max supply) = (Vo(peak) + Vd)( Transformer voltage regulation)(Line land variation)

Vo(peak) ^2 = RL * P*2.

Vd = voltage lost across the tube
Would Vd be the voltage across the plate resistor or what voltage from the data sheet would be used?

 

You will need to check the data sheet of the tube(s) you plan to use. Also you need to know whether you are going to use a triode, pentode or beam tetrode and if the latter two if you are going to use those in triode connection.
For example a KT66 in triode connection drops 100V at Vg=0 and 100mA, so you need to add 100V to the input voltage to the transformer. In pentode mode you might get 200mA at only 50V drop. Then there is "ultra linear" mode that is somewhere between, but it also depends on what voltage you plan to run Vg2 at.

 

You will need to check the data sheet of the tube(s) you plan to use. Also you need to know whether you are going to use a triode, pentode or beam tetrode and if the latter two if you are going to use those in triode connection.
For example a KT66 in triode connection drops 100V at Vg=0 and 100mA, so you need to add 100V to the input voltage to the transformer. In pentode mode you might get 200mA at only 50V drop. Then there is "ultra linear" mode that is somewhere between, but it also depends on what voltage you plan to run Vg2 at.

I am looking to use an set of 6L6-GC Beam Pentode in a Push Pull type amp close to a B type amp.

 

One thread is enough for the same topic.

Pre(Solid State) to Power (Tube Amp)
https://forum.allaboutcircuits.com/threads/pre-solid-state-to-power-tube-amp.142172/