Current calculation from datasheet

[boyofwax]

Regarding this datasheet: http://www.drtube.com/datasheets/ecc82-philips1969.pdf

@ Operating characteristics AF amplifier one unit
First column Vb 100v and Ra 47K

Can someone show how Ia (1.2mA) is calculated?

[DualTriode]

Originally Posted by boyofwax

Regarding this datasheet: http://www.drtube.com/datasheets/ecc82-philips1969.pdf

@ Operating characteristics AF amplifier one unit
First column Vb 100v and Ra 47K

Can someone show how Ia (1.2mA) is calculated?

Hello boyofwax ,
The calculation you are asking about is a tough one. You listed some operating conditions; B+, current and Ra value. There are other things that also need to be included such as connected load.
The item, current, you are asking to calculate is more a as measured and reported in the data sheet thing than a calculated thing.
A Spice program or other Computer Aided program such as Tube CAD: Tube Audiio Design Software include a complex mathematical model that will do those calculations. The spice models contain some not totally accurate assumptions that output more a Scientific Wild *** Guess, SWAG.
TubeCad is an interesting program to play with. You can see the results of adjusting things such as B+ voltage, Plate resistor, cathode resistor ect.
DT
All Just for fun!

[DF96]

1.2mA is not calculated, it is measured or read from a graph in the datasheet. A valve model as used in Spice is an attempt to calculate current so that it looks something like a real valve.