Proper Grounding for chip amp

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I've been reading a lot of posts here and now I am confused about grounding.
When this board arrived I hooked up a 12.6-0-12.6 transformer and the speakers, plugged in a sony walkman and I played this all night.

Now I have it in a case and I have some questions,

Do I need to use silicone pads, the heat sing is inside a case.
Do I need to ground the negative speaker returns to earth?

Just curious because it worked fine without grounding everything.
Ground and earth are two different entities. You should not ground the negative return if it is working the way u made it. However grounding the chasis is required at the psu ground point, at the filter capacitors.

However, what to do with the earth connection(third point on mains) is a subject of much more knowhow...and priorities.

Gajanan Phadte
You must have a Safety Earth.
The third wire (PE = green or green/yellow) in mains powered equipment MUST be Directly CONNECTED to the Chassis.
This is not optional !!!!!!!!!

Some manufacturers build equipment to ClassII regulations. These do not have the PE wire and thus cannotbe connected to Chassis.
The design and manufacture and testing and guarantee that apply to ClassII products cannot be replicated by us Members.
We can only build ClassI equipment.
my earth ground is going to a transformer mounting bolt even though the case is all plastic exept for the aluminum face plate.
Interesting case, it is an old parallel switcher for 2 printers. It was sprayed with some sort of shielding that had a consistent 10ohm reading.

I'm a maintenance person so I understand the 120/240 side of electric.
This is my first electronic build and just wanted to make sure I am grounding the amp correctly.
I should be listening to this in the morning.
Once you have the Safety Earth in place, then you must look at the next safety requirement.

All exposed conductive parts must be connected to Protective Earth.

This does not need to be a Direct to Chassis connection, although this would be the highest standard of safety.
You can use a Disconnecting Network (DN) between Main Audio Ground and Chassis.
This DN MUST be able to pass FAULT current of the order of 1000Apk until after the mains fuse ruptures and the arc extinguishes.
As far as I am concerned there is no reason for an ungrounded plug.
I have taken many pieces of gear apart and the ones without the 3 prong plugs have a small fortune in plastic stand offs.
The reasons I used a plastic case is it cost me 10 bucks a decade ago and I had no use for it and I like to recycle items. I have a couple of useless tuners and cassette decks that may become small amps one day.
The biggest challenge is getting the power supply in a small box.
I have a couple of Commodore floppy drives that would make interesting amps.
I attempted to put this system in a commodore power supply box but I would need 2 of them, one for the amp and 1 for the power supply.
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