text: 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_56 (det_pre_amp VARCHAR, _number_tubes VARCHAR, rectifier VARCHAR)
  ### Question:
  Name the det/pre-amp with # tubes of 4 and rectifier of x
  ### Answer:
  SELECT det_pre_amp FROM table_name_56 WHERE _number_tubes = "4" AND rectifier = "x"