Iconv UTF-8 to ASCII EXTENDED

Ruby 1.8.6
Rails 2.3.2

The DB is runnig with UTF-8 codification.
I need to export some text field from the DB to TXT file for import
with another app runnig under DOS (no comments please...). I am having
problems exporting texts containing chars like á, ú or é.
Here an example os the behaviour:

#code
require 'iconv'
text = 'aeú'
Iconv.new('ascii//translit', 'utf-8').iconv(text) -> Raise an error.
Iconv.new('ascii//ignore', 'utf-8').iconv(text) -> 'ae' (ú was
truncated)

How can I convert chars (like ú), with ASCII codification greater than
127, correspondig with the EXTENDED ASCII charset ?

Thanks
Fabian