You can try a bunch of different ways of grounding to get the best hum reduction.
You can divide it up into three grounds:
1) power line ground- the green wire.
Usually a connection is made to the chassis right after the wire enters the box thru the grommet.
This is a no brainer.
2)I/O jacks
This is where things get tricky.
Some people mount the I/O jacks next to each other for flux loop reduction.
Others prefer a more logical approach, like In's on the left, Outs on the right, or In's on the front, Out's on the back.
You can use either way, but you might have to move some Pin 1 shield grounds around to make this work with low hum.
3) Now we are just left with the electronics ground.
This wire provides a return path for the electricity back to the power supply after they have done their work via the tubes and resistors and of course, transformers.
But audio is also super imposed on the DC current in the form of AC audio, which gets separated out of the DC via the caps.
But there could be some noise currents in the chassis from your green wire ground, and our Pin 1 shield grounds.
So you want to run a separate ground, strraight from the minus side of your power supply, directly to the electronics ground.
This will keep you from getting those nasty noise currents in your audio output.
A good grounding technique is to use a huge soldering iron to make an ultra low resistance, and therefore an ultra low hum connection to ground.
It's one of those tools that you keep in the closet and use once per chassis, but man, it will pay for itself after the first joint is made.And it stays this way over time.
Nuts and bolts can corrode over time, which means your ohms on your ground will go from 0.01 to 0.02 ohms, doubling your noise.
The soldered ground will come out to around 0.000001 ohms, but that is just a guess, you need a four wire meter to measure these low ground connections.
