Write a string as a ASCII format to a data file

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C#

Dear Friend:

I have a string that comes from a textbox. I want to write this string in the format of ASCI to a file. I use various method but i do not get any result.
for example:

private static Encoding encoding = Encoding.ASCII;

private static byte[] CSTB( string cod, Encoding enc )
{
    byte[] transformacion = enc.GetBytes( cod );
    return transformacion;
}

private void btn_CreateNewCard_Click( object sender , EventArgs e )
{
FileInfo finfo = new FileInfo( path );


    using(FileStream fs = finfo .Open( FileMode .Open ,FileAccess .Write ,   FileShare .ReadWrite ))
    try
    {

        fs .Write( CSTB( "Moha",encoding  ),0, CSTB( "Moha",encoding  ).Lenght);
     }
}

Is that my code correct?
Why I see the original text ("Moha") when I click my button?

Yours