C2200: How do you get the top off?

I'm trying to change the tubes in my McInotsh C2200 and I removed the 6 black screws on the chassis but the lid won't come off. It seems to be held on in the front by some invisible screw. I don't want to tug at it and damage the glass front.

I no longer have my C2200 but I recall changing tubes.
If I recall correctly, when all screws are removed the top is ready to come off. The top piece must be pushed or pulled towards the BACK of the unit. Kind of walk it back and forth as you move it towards the rear. The front that you think is secured is just inserted into a narrow channel to hide and give the finish look.
I do not recall any fasteners under or around the front.
The top is slide under the front extrusion when you replace it.
Check for screws also on the side? I cannot recall that area.
hi pookie,the lid isnt held on by a screw it kinda locks in place under the top rail,you need to lift from both sides in the rear & tilt the rear of the lid upwards then it will slide out,if you are trying to lift the entire top lid at once it will never come off,if you look real close you can see that the leading front edge of the lid is wedged under the top rail.

I have a C2200 and have changed tubes many times - finally settling on NOS Amperex - a tremendous improvement over the stock Chinese tubes.
In addition to the screws on the sides there are two on the back. After all are removed you do have to carefully pry it backwards (and upwards ad Bigjoe suggests); there are no other (hidden) screws. After the top has been removed the first time, it comes off easily in subsequent removals.