This is the chassis just after attaching the xformers, sockets, and ground plane points. Lots a wiring to follow. Take special note of these ground plane points, they are located in many different parts of the chassis.
The reason for the multiple locations of ground lugs is simple- all grounds are not created equal.
These points all have different paths and impedances to the "real" ground. These paths are like rivers of current carrying ac and dc signal out of the amplifier, some are further upstream than others.
Its important to note that some points carry more "dirty" signal that are the byproduct of dc filtering. Placing a sensitive ground point in the path of these dirty grounds can inject noise into the circuit... Hummmmmmmmmmmmmmmm
We want to keep the most sensitive stages of the amp as far upstream as possible. The most sensitive stage of the amp is the input. Keeping all this in mind and utilizing your brain gives you the best chance for eliminating noisy loops and gives you the best chance for a nice quiet amplifier.
The lugs closest to the power inlet are the closest impedance to real ground, the one that is on your house or studio structure. This is the end of the ground plane for our purposes…
A nice solid 24k gold spike inserted into the earth would be an ideal final ground point, but it probably would get stolen. -Ossie