Filter Table , Column by postion

Hi, 

  so filter table ;

Table.SelectRows(Source , each ([B] = "A"))

but if I do not know the name of a coliumn, just postion, so I know I need column 2 , so I found the name; 

 ( List.Transform( {1}, 
(A)=> Table.ColumnNames( Source ) {A} ) {0} )

So this is giving me the column name as text, but how to I get into the select rows as a column , Table.Column = a list, 

 List.Transform( 
 Table.Column ( Source , colname ), 
 (A)=> A = "A")

So is there a way to get colname  step which is text into the equivalent of  [ column name]  ? 

Richard.