pg_ [dump & restore] invalid archive problem

Hello List... I'd like to move a db containing large objects from one db to
another.
Using the command syntax directly from man pg_dump:

      pg_dump -Ft -b mydb > mydb.tar

      pg_restore -d mydb mydb.tar

I invariably (tried various attempts) get the following error:
"pg_restore: [archiver] input file does not appear to be a valid archive"

Any help much appreciated.
/j-p.