Is it ok for tube amp directly to the outlet?

Sounds like you are where you would want to be on this wiring schema.

Actually, I have a 80A line from the main panel to the subpanel and from the subpanel to 4 outlets in the room. All the gound lines from the outlets go to subpanel ground and the subpanel ground to the house's main ground.

Is the subpanel's ground line should be separate from the house's ground line and is this dangeous, violate the city's code if I separating them?

If subpanel ground shares with house's main gournd, is this called dedicated line or are they must be separate ground lines?

Thanks!

Directly to the wall should be the unanimous choice.
You already know the sound using your line conditioner.
Try the amps directly to the wall.You will be surprised.

Another recommendation here to go straight into the wall. If you don't already have a dedicated electrical line coming to the outlet, do that before reverting back to a power conditioner.

Most conditioners limit current, therefore you are better off going straight into the wall. Cheers,
Spencer

Tubes are not damaged by voltage spikes that would zap transistors.

if you plug direct into wall I'd make sure you have a dedicated 20 amp line and I'd routinely only plug the amp in when using it.
Larry

I think it is better to plug directly in all occasions except one.
You will get some little (or more) grunge but you will also gain dynamics and what's usually termed "ease of drive". Try it.