Loop through Recordset for Duplicate Values / Append Value to Separate Table

I need to loop through a filtered recordset to check the value of a field (Table A, Field A). If each value of the field in the recordset is the same, I need to take that value and append it to a field in a separate table (Table B, Field A).

So, it would look something like this:

Table A
Record 1, Field A = 6
Record 2, Field A = 6
Record 3, Field A = 6
Record 4, Field A = 6

becomes . . .

Table B
Record 1, Field A = 6

If the recordset values are not the same, then the field value in Table B is a Null. Thanks.