Updated text fields to JSON string - Javascript/JQuery

I have a dynamic form that has text fields which change to input boxes when they need to be updated.

When they have been updated and the user clicks submit I want to add the updated values to a json string which i can post to an ASP.NET script.

Here is the html of 2 rows in the table:

Colleague 1:

    


    



    


    


    
    Del

     Colleague 2:

    



    


    


    



    
    Del

Here is the jQuery I'm using to detect which input boxes have been updated:

$("#subdetails").click(function () {

    $("#mantab input[type=text]").each(function () {
        if ($(this).val() !== this.defaultValue) {               

             //code to create json string   

        }
    });
 });

This is an example of a json string i would like to create if the following field were updated:

{
"1":{
    "c1nametb": "newname",
    "c1exttb": "22227",
    }
"2":{
    "c2eaddtb": "neweadd@company.co.uk",
    "c2pnotb": "0111122210",

    }
}

Can any one please help me with the code to create this string, or advise on a better way of doing this?

Thanks
Ryan