[Amps] RL Calculations

[Bruce Osterberg]

Good Morning:

In an Effort to calculate the RL of my two Tube 3cx1500A7, (8877 Amp) 
Usually the formula is Voltage on the Plate,  (Ep), divided by 1.8 x Ip. 
  My question is for this calculation do you use the Voltage that 
appears on the tube plate key Up, ( my case 3900 VDC)  or Key Down 3500 
VDC.
Thank you.  160 meter amplifier Only  Calculating for C1, L1, C2, L2 in 
a Pi-L Network.

Bruce N9BX 73