Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE table_name_69 (rectifier VARCHAR, det_pre_amp VARCHAR, _number_tubes VARCHAR)
### Question:
Name the rectifier for Det/Pre-amp of x and # tubes of 4
### Answer:
SELECT rectifier FROM table_name_69 WHERE det_pre_amp = "x" AND _number_tubes = "4"