Choke Loaded Driver Load Lines Question

[Troncones]

I'm reverse engineering a bread board SE 2A3 amp I picked up. It uses choke loaded 6SN7GTs to drive the 2A3s.

When drawing the 20hz and 20khz load lines do you use just the impedance of the choke or do use the choke impedance parallel with the 2A3 input impedance?

[DF96]

Remember that only a resistor gives a load line. Adding reactance gives a load ellipse.

[Troncones]

The only info I have is posts I have found here and there. I do recall somebody mentioning a ellipse. Can you expand a little on this or point me to some text and equations?

[Troncones]

I found the text and math needed for this application. Now I know why there was very little input on the subject. Creating the load ellipse looks like a lot of work and not much fun. What really impresses me is to think people use to work through problems like this with just a slide rule.

I'm guessing there is software out there to model this application.

[dsavitsk]

Yes, it's an ellipse, but for practical purposes, the impedance of the choke, anywhere above 100Hz or so, is so high that it can be ignored. Thus, it is the next stage (probably the grid leak resistor) that matters and provides the "real" load.

Now, if you have a grid choke on the next stage in addition to your plate choke, things are both harder and easier. Harder because the math is tough and there is likely to be interaction between the chokes, easier because it hardy matters -- the load line is almost horizontal.