How can I hang a 55 inch TV from old plaster?

You have to locate the studs behind the plaster to secure the TV hanger to something solid . You can purchase a stud finder at a hardware store . they are not costly .

I thought that might be true but I don't know how to do that but my friends will put it in for me Thanks

Don't chance it, why not something like this?

Due to the age of the house, and in keeping with its character, have you ever considered concealing the tv in an armoire rather than hanging a modern piece of electronics directly on the wall?

What about hanging a piece of nicely painted plywood with those red rocket screws. The screws com in all sizes. One in each os the tote corners of plywood. Then mount the TV wall swivel on the plywood. Just a through.

Carolyn from NH

You need to find out three studs. Screw a 2X2 inch board to it and then put your TV on that. I did this with a very large heavy mirror and it is still up with no problems.

You need to screw it into the studs only wi.th anchors