Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_56 (det_pre_amp VARCHAR, _number_tubes VARCHAR, rectifier VARCHAR)

### Question ###
Name the det/pre-amp with # tubes of 4 and rectifier of x

### Accurate SQL ###

SELECT det_pre_amp FROM table_name_56 WHERE _number_tubes = "4" AND rectifier = "x"