The Two-Point Earth Method
Red is earth of signal. Green is earth of power supply.
The main earth line's diameter is more than 3mm.
The signal earth line's end is connected to the input terminal and output
This line connects with the chassis at one point near the input terminal.
The power supply earth line connects with the chassis at one point near the power transformer.
In the example of the Sakuma phono preamplifier:
The earth of the top tube 5691's filament is not connected to the main earth line.
Its earth point is the output terminal.