Convert tabs to spaces in tcl??

Using tcl, I'm reading through a file generated by a report-writer. There are some records that have tabs in them, some don't. I need to parse out the fields (columns in the report) positionally. The problem is using string range or crange views the \t in the records as single characters

I tried doing
regsub -all $rec \t "     " rec
but since the amount of whitespace in a tab is not static, I was getting undesired results.

Example of report line:
10/27/08                   801062347       801062347                .00    Charge                  70.99       N
Corresponding example of octal display from the report file:
0001460   \r  \n   1   0   /   2   7   /   0   8                  \t  \t
0001500                8   0   1   0   6   2   3   4   7  \t
0001520    8   0   1   0   6   2   3   4   7  \t  \t                   .
0001540    0   0                   C   h   a   r   g   e  \t  \t
0001560        7   0   .   9   9                               N  \r  \n

I'd prefer to handle this in the tcl script but if necessary, I suppose I can manipulate the file using ksh beforehand, although I'm not sure how I would do that either.

Any ideas?