Translation:Shulchan Aruch/Orach Chaim/54
54: Laws Relevant to Yishtabach. Contains 3 seifim.
1 Yishtabach does not start with Baruch because it is adjacent to Baruch sheamar, for both were instituted for pesukei dezimra – one before them, and one after them.
2 One does not say amen after "melekh mehulal batishbahot", but instead after "hai haolamim", which is the end of the berakhah.
3 One who speaks between Yishtabah and Yotzer – it is a sin in his hand, and would be required because of this to return from the battlefield. And there are those who say that it is permitted to interrupt for communal needs or to bestow charity to those who come to be provided for from charity. Gloss: And from this spread the custom in many places to say a blessing for the sick or for a claimant to ask for judgement at the synagogue between Yishtabah and Yotzer, because all of these are instances of the purpose of a mitzvah. And after that, when they resume praying, the leader should say a bit of pesukei dezimra and should say kaddish on them, since we never say kaddish without a psalm before it. And this is why the evening service begins without a kaddish [Kol Bo]. And likewise, one who did not have tzitzit or tefillin and one was brought to him between Yishtabah and kaddish, can put them on and say the blessings on them. But between kaddish and Barkhu, one must not stop for any purpose [Or Zarua, Chapter "Prayer of Shacharit"], and all the more so, not stop after the leader has said Barkhu, before they begin the Yotzer blessing. [Beit Yosef, end of Chapter 57 in the name of HaManhig; and see below, end of Chapter 56].