In this paper (http://science.uniserve.edu.au/school/curric/stage6/phys/stw2002/sefton.pdf) the author describes the transfer of energy in an electrical circuit as follows: "To explain energy transfer we need to look at what is happening outside the wires. As a consequence of the surface charges on the wires, there is an electric field in the space outside the wires (as well as inside). Also, as a consequence of having a current in the wires, there is a magnetic field in the space around the wires. It is this combination of electric field and magnetic field in the space outside the wires that carries the energy from [source] to [load]. Once the fields are set up, the energy travels through space, perpendicular to both the electric field and the magnetic field, at the speed of light." I've read similar descriptions in a number of places, often accompanied by a diagram showing the various fields that are participating in this energy transfer, like this: Now here are four photos of alternative layouts for the filament wiring in vacuum-tube amplifiers: (The bottom right amplifier uses the chassis as one of the conductors in the filament circuit.) The total current carried by these wires is typically 2 to 3 amps, and the voltage (most often AC, but sometimes DC) is usually 6.3 volts. A similar variety of layouts can be found in the high-voltage portions of such circuits as well. Now based on the diagram above, I would think the electric and magnetic fields in these various configurations would be significantly different. As different, perhaps, as the diagram above and, say, this one: And yet I've found (in spite of the claims of various aficionados) no significant subjective difference in the performance of such widely different layouts; and certainly no objective difference in the voltage and amperage readings at the corresponding spots. Sure, we might get a little more or less hum one way or another (though, in practice, that's not as easy to predict as one might think); but we never see a significant change in the voltage or current based on the layout. In other words, it seems to me that while these various fields may be truly present as described, it's hard for me to imagine that they are the primary conduit for the transfer of energy in such circuits. Seems to me that the energy is being transferred through the actual conductors (wires or chassis or both), not via the space surrounding those conductors. Comments?