Can you relate this explanation to the "Source Impedance" of the secondary of the transformer to the input of the first filter element? Thanks. Or the primary of the OPT to the plate of the power tube? That would be helpfull. I have a very comprehensive library of electronics reference books as well as explanations on the net from Rod Elliott and Bas and others. But you are building a data bank of explanations that can pull all this info together in a simple line of responnses that reflects well on ART. Thats why I persue this with you. If it becomes tiresome then I of course will cease and desist. Anyone can learn but few can teach. Wayne is a good example of speaker explanations; you do electronics.