Your question is either unclear or wrong. I made myself the following test file :

Hallo	Da
Dies	Test
Ist	ein

And your script works as I think it should, as it prints out :

A    Tab
Hallo    Da
Dies    Test
Ist    ein
[download]

Maybe you should rephrase your question ... Is it maybe that you have a literal "\t" (and not the TAB character) ? Then maybe a regular expression replacing \t by \009 would do what you want ...

  s/\\t/\009/g
[download]